Note: Descriptions are shown in the official language in which they were submitted.
Description
Elevator System Having Microprocessor-
Based Door Operator
Field of the Invention
The present invention relates to improvements in
elevator systems and particularly to a micro-
processor-based door operator system. The invention
will be described as part of a novel hydraulic eleva-
tor control system, but is shall be understood that
the door operator may be employed in other elevator
systems.
Backqround of the Invention
Hydraulic elevators include a hydraulic jack
which i5 mounted in the hoistway pit and supports the
elevator car. A pump unit supplies hydraulic fluid
from a reservoir to the jack through a solenoid-
operated valve that includes flow regulating pistons
for selectively raising and lowering the car. The
valve is, in turn, operated by a control system. The
control system performs the functions of receiving
hall calls and car calls, dispatching the car to the
appropriate floors, stopping the car level with the
floor landings, and opening and closing the doors.
Part of the overall control system is a selector,
which senses the position of the elevator car in the
hoistway and determines slowdown and stopping points.
Traditionally, all of the control functions of a
hydraulic elevator have been performed by relay cir-
cuitry centrally located in the machine room adjacent
to the power unit. Car position signals are provided
by switches mounted a~ appropriate locations in the
hatchway. ~he switches are actuated by cams mounted
on the car and the signals are brought to the con-
troller by a hoistway riser.
,~
`
A door operator mechanism is mounted on top of
the elevator carO It includes a motor, pulleys and a
linkage connected to the door, and cam-operated micro
switches actuated at various points including the door
open limit, door close limit, and door slowdown
points. Switch signals are fed to the controller
through wires from the hoistway. Thus, the contr~ller
is physically adjacent to some of the machinery it
controls, but is remote from the door operator and to
the external signals it requires.
Microprocessors possess a number of potential
advantages over relay-based controls from the stand-
point of system flexibility. It would be desirable,
therefore, to replace the door operator relay controls
in a hydraulic elevator with a microproce9sor con-
troller, provided that such a control could be
employed with hydraulic elevator hardware in a cost
effective manner.
As noted before, traditionally the controller and
power unit are located in a machine room. The opera-
ting temperatures and vibrations of the power unit
make the machine room a relatively inhospitable
environment for delicate components such as micro-
processors. It is not practical, then, to substitute
a microprocessor control for relay circuitry without
either taking special protective measures or utilizing
components having higher specifications than that of
typical industrial or consumer-grade components. This
is unde~irable from the standpoint of the higher costs
involved.
Alternatively, as one manufacture has done, the
microprocessor control may be relocated to another
location such as on the car. However, the control
circuitry in conventional hydraulic elevators is
located in the machine room in order to be located
close to the power unit, thereby minimizing the amount
of power wiring. Relocating the control would require
then additional wiring so that the microprocessor will
5~6~
still be able to communicate with the machinery and
power supplies in the machine room and switches in the
hoistway. To reduce installation cost and to improve
reliability it is desirable to keep the amount of
wiring to a minimum.
Each microprocessor has inherent limitations in
terms of its input/output capabilities (number of I/O
ports), processing capabilityt and speed. In any
control system for an elevator, it is undesirable to
have delays in processing and transmitting critical
inormation, such as slowdown and stop signals, cer-
tain door control signals, and safety information. At
the same time, it would be desirable from the stand-
point of cost ~o minimize the number of dedicated
terminals used by the central control for input/output
with peripheral devices, to perform control unctions
using minimum microproces~or capability, and to per-
form critical decision-making functions with a minimum
of delay.
SummarY of the Invention
The present invention is a microprocessor-based
door operator which is particularly suited for an
elevator system employing a distributed intelligence
control system. By way of example, a hydraulic
elevator including a control system is separated into
four operating subsystems: a car logic controller
("CLC"), a selector, the door operator, and a power
controller. The CLC, the door operator, and the
selector are all mounted on the elevator car, and each
is microprocessor-based. The power controller
utilizes relays for certain control functions that are
not incorporated in the CLC or other microprocessor
based subsystems. The CLC is linked to the door
operator and selector over a serial communications
link, and utilizes a polled network protocol. The
power controller is controlled by signals from the CLC
and, in certain instances, from the selector.
--4--
In this illustrative system~ each of the sub-
systems, including the door operator, carries out
certain functions at the instruction of, but separate
from the CLC. Accordingly, each of the subsystems
carries out it5 intended functions inclependent of the
limitations of the processing power and speed of the
CLC microprocessor and independent of the speed of
data transmission by way of the serial communications
link. Communications between the four operating sub~
systems may be accomplished using a minimum of wiring
and using microprocessor components matched to the
processing capabilities of the particular subsystem.
Each subsystem microprocessor is assigned a unique
address, which makes it possible for any subsys~em to
communicate with any other subsystem.
Preferably, the communications link includes
external access connectors for a portable terminal, to
input data into the door operator and read data from
the door aperator.
In the exemplary system, the control functions
are distributed among the subsystems. The CLC
receives and latches hall calls and car calls, and
sends enabling relay signals to the power controller
to initiate elevator car runs and control slowdown.
The CLC receives signals from the selector indicative
of car position floor and slowdown points. The CLC
also instructs the door operator as to when to begin a
door open cycle, and also controls door open times.
The door operator includes a pair of microproces-
sors and performs all the control functions for thedoors except for the decisions about when to open and
close. The door operator controls opening speed and
stopping of the door. It includes a standard opera-
ting cycle, in which it will reopen the door upon
actuation of the door edge guard or light sensing
device. It also includes other cycles of oper~tion,
in which the door will not completely reopen, or will
ignore electric eye signals and attempt to close
--5--
~;295~
the doors at a reduced speed, i.e., "a nudging" opera-
tion. These operating cycles are programmed in the
door operator microprocessor and the cycle selected
for operation is determined by the CLC.
During door operating cycles, the door operator
controller operates responsive directly to door edge
and electric eye signals (or other obstruction detec-
tion devices), without going through the CLC, and
therefore can respond instantaneously.
The CLC supervises and co~trols the other sub-
systems. But each of the other subsystem has pre-
assigned decision making functions that are executed
independent of the CLC. In view of the fact that the
system includes a number of dedicated microprocessors,
the critical control functions for elevator operation
are not limited by the power capability of the CLC, or
by the time limita~ions of serial communication
between elements.
Brief Description of the Drawinq
Fig. l is a front, schematic view of a hydraulic
elevator system in accordance with the inventlon;
Fig. 2 is a schematic drawing of the control
subsystems of the elevator according to Fig. 1;
Fig. 3 is a schematic circuit diagram of the car
logic controller (CLC);
Fig. 3a is a schematic circuit diagram of a group
operation in accordance with the invention:
Fig. 4 is a schematic circuit diagram of the
selector;
Fig. 5 is a schematic circuit diagram of the door
operator;
; Fig. 5a is a schematic drawing of an H-bridge
door motor control;
Fig. 5b is a side view of a door operator
housing;
Fig. 5c is a top sectional view of a door
operator housing;
Fig. 5d illustrates an exemplary operation of the
control of Fig. 5a;
Fig. 6 is a schematic dra~ing of the power con-
troller;
Fig. 7a, 7b, and 7c are schematic flow dlagrams
of the operation of the CLC, selector, and door opera-
tor in accordance with the invention.
Fig. 8 illustrates a portable terminal for acces-
sing the communications link;
Figs. 9 & 10 are front and side views of a
selector tape in accordance with the invention;
Fig. 11 is a perspective view of a selector
housing and selector tape in accordance with the
invention;
Fig. 12 is a front view of a portion of the
elevator guide rail and selector tape together with
the selector hou~ing and swit~h assembly mounted on
the car;
Fig. 13 is a front view of a section of the
selector tape, showing an arrangement of magnets for
indicating floor position and door zone;
Fig. 14 illustrates the magnetic readouts of a
pair of vertically spaced-apart magnetic sensors and
positioned to detect the holes of a tape in accordance
with Fig. 13;
Fig. 15 is a top view, partially in section of
the selector housing shown in Fig. 11; and
Fig. 16 is a front view of the sensor mounting
board shown in Fig. 15;
Detailed Description of ~ Preferred Embodiment
Fig. 1 shows a hydraulic elevator system that
include a car 10 vertically displaceable in a hoist-
way 12 between landings. One of the hoistway landing
doors is indicated at "G". The car 10 is raised and
lowered by a hydraulic jack 14, which is supplied with
hydraulic fluid from a pump unit 16 through a valve
18. An example of a preferred valve 18 is the I-2 or
I-3 Oildraulic~ Controller manufactured by Dover
Elevator Systems, Inc. The valve 18 includes
solenoid-operated valves controlled by a power
controller "P".
Oil is supplied from the pump unit 16 to the
valve 18 through supply and return lines, indicated by
20, and from the valve 18 to the hydraulic jack 14 by
a fluid line indicated by the numeral 22.
The car, shown schematically in Fig. 1, includes
a door 24, a swing return panel 26, ~nd a door opera-
tor mechanism 28, which includes a door operator
housing 30 and motor 31. The motor 31 may be coupled
to the door 24 using a conventional pulley and linlcage
arrangement, or in any other suitable manner. The
coupling means, being well known, is only partially
shown in Fig. 1.
Elevator operation is controlled by four inter-
connected subsystems: a car logic controller (refer-
red to herein as "CLC"), which is mounted in the swing
return panel 26; a door operator "DO" which is cvn-
tained in the door operator housing 30; a selector
"S", which includes a tape system 300 mounted in the
hoistway and a sensor housing 320 mounted on the car,
and which also includes a switch tree assembly "SW"
mounted on the car and cams "C'l mounted in the hoist-
way; and, finally, the power controller "P" mentioned
above.
The elevator system employs a distributed intel-
ligence control, in which the CLC, door operator DO,
and selector S have specific control responsibilities.
Each includes a microprocessor for performing the
designated functions of the subsystem, and also for
communication with the other subsystems. The CLC,
selector, and door operator microprocessors communi-
cate over a pair of common communication lines 32, 33,as shown in Fig. 2, by way of a serial communications
multi-drop link. As also indicated by Fig. 2 the
selector "S" may communicate directly with the power
;
-
- -
,
-8-
controller "P" over communication line 37 as described
further below. Finally, selector S communicates
directly with an input of the CLC microprocessor over
line 38 for providing a slowdown interrupt signal
"SDI", also described further on.
An example of a suitable communications interface
standard over links 32, 33 is RS485. Each of the
microprocessor subsystems has an assigned address and
employs suitable RS485 drivers and receivers for send-
ing and receiving signals. The CLC acts as communica-
tions controller, and systematically polls the other
devices, i.e. it sends out addressed communications
and can receive responses within certain time windows.
In this manner, other microprocessor subsystems, such
as a rear door operator, may readily be connected into
the system, requiring only the appropriate so~tware.
Also, a portable diagnostic terminal may be connected
to the link, and the CLC polls for its presence. As
indicated in Fig. 2, the CLC also has serial output
terminals for group operation.
Communication between different devices is accom-
plished over a twisted shielded pair of wires, prefer~
ably using a technique called differential communica-
tion, in which one signal is the complement of the
other signal. In order for each device in the com-
munication to know who it is talking to, the door
operator, selector, car logic controller, and external
terminal are each given an addressO
Actual communication protocol is arranged in
group call packets including a start flag, destination
address, source addres , type and length information
and data field and finally a check sum. This multi-
drop, differential RS~485 system ensures reliable
communication control.
Referring once again to Fig. 1, a diagnostic tool
connector DT is provided physically adjacent to each
of the subsystems CLC, DO, the power controller, and
S. The connectors DT provide access to the
_9_
communications link 32, 33 for an external plug-in
device, i.e. a terminal of the type shown in Fig. 8.
Standard multi-pin connectors and sockets may be used.
The CLC transmits control signals to the power
controller P over a series of wires 34, and receives
input signals from the hoistway riser over wires 35.
The wires from the car are carried by a travelling
cable 36. As indicated by Fig. 1, travelling cable 36
also carries the communications link 32, 33 to the
area of the power controller P where it is connected
to a diagnostic terminal connector DT. The travelling
cable 36, carrying signal links 34 and 35 and communi-
cation wires 32, 33, is connected between a terminal
39 in the car and a junction box 40 mounted on the
hoistway wall at about the mid-point of elevator
travel. The travelling cable 36 also carries current
from the power controller P to the car for power
supplies associated with the microprocessors, the door
operator motor 31, the lights and fan, push buttons,
and so on.
Fig. 3 illustrates schematically the car logic
controller or CLC. The CLC, which is physically
located in the swing return 26 (Fig. 1), includes a
printed circuit board 50 containing integrated cir-
cuits, including a microprocessor chip 52, an EPROMchip 54, memory chips, e.g. RAM 56, and serial inter-
face devices indicated at 58, 59. An example of a
,~,r,,~,~ suitable CLC microprocessor is a Motorola~6809.
Preferably, if volatile chips such as RAM 56 are used
for memory, a battery 57 is mounted on the board to
retain memory in the event of a power failure or shut-
down. The device 58, by way of example, is an RS485
type receiver for inputting signals into micro-
processors 52, and device 59 is an RS485 type driver
for outputting microprocessor communication signals to
the serial communications link 32, 33.
The board 50 also incorporates devices 60~
labelled I/O, necessary for the CLC microprocessor to
* ~'`~ vle ~
--10--
communicate with external devices, such as car call
buttons, car signal fixtures, call registered lights
(hall lanterns), and hall call buttons (the l~tter
being supplied over line 35 from the hoistway riser),
and also to supply output signals over lines 34 to the
power controller P. I/0 interface devices 60, e.g.
for converting voltages, are known.
A power supply 62, mounted in the swing returnS
supplies power to the CLC microprocessor and can also
supply the door operator and selector microprocessors.
The power supply 62 gets its power from the power
controller over the travelling cable 360
The portable diagnostic terminal 66 shown in Fig.
8 plugs into any of the connector~ DT through pin
connector 68. If desired power can be supplied to the
terminal 66 from one of the available power supplies,
e.g~ the power supply 62 or the power controller power
supply (24 VDC), through one of the connector channels
in connector DT, to obviate the need for an on-board
power supply in the terminal 66. The device 66 is not
required when the elevator is in normal operation and
i~ unplugged. Since all of the connectors DT are
connected to the common link 32, 33, the CLC, selec-
tor, and door operators all may be accessed from any
of the locations.
Referring to Fig. 3a, the CLC in accordance with
the invention includes a software section for group
operation. In the event the car is to be operated in
a group, the second car is connected into a pair of
CLC I/0 terminals assigned to group operation, prefer-
ably by connections made between the power controllers
of the two cars as shown in Fig. 3a. Communication
between cars is preferably via a serial communications
link using communications protocol similar to that
used among the car microprocessors.
Any microprocessor has a limited ability to
address I/0. As will become apparent, in view of
using serial communications protocol, and in view of
~,5~
the distribution of control functions (and therefore
distribution of control responsibilities of communica-
ting with external devices), the control functions of
the CLC utilize a relatively small number of I/O
ports, and leave free terminals for performing other
functions such as safety and fault monitoring.
Distributed control with serial communications there-
fore reduces I/0 cost and space requirements.
The selector S is illustrated schematically in
Figs. 1 and 4. The selector subsystem is a
microprocessor-based control that provides signals for
slowdown, levelling, and position. As indicated in
Fig. 1, the selector subsystem includes three func-
tional components: (1) the tape system (which com-
prises a stationary tape 300 and a sensor housing320); (2) a switch device "SWI' wi~h cams "C", and
(3) a processor board 74. ~n example o~ a micro-
processor suitable for a use with a selector in accor-
dance with the invention is the Motorola Model 68701,
which includes on-board, programmable memory.
All of the selector active components are mounted
on top of the elevator car, which reduces hoistway
wiring associated with the selector function. The
mechanical configuration of each of these components
in described further on.
The tape system includes a sensor 70 that derives
three sets of signals: levelling, floor position, and
travel distance. More specifically, the sensor 70
derives the following signals from the tape 300: door
zone DZ, indicating that the car is within a specified
distance of the landing; level up LU, which indicates
the car is in a region just below the landing; level
down LD, which indicates the car is in a region just
above the landing; floor identification, which may be
read as binary code signals, and travel distance,
which may be pulses representative of travel.
LU and LD sensors are activated when the car
drifts a certain distance away from the landing. The
distance the car is permitted to drift without activa-
ting the LU and LD sensors is called the dead zone.
Preferably, a plurality of level up LU and level down
LD sensors are provided at different spacings and a
pair of LU and LD sensors are selected dependent upon
the desired dead zone. A levelling jumper selector 76
may be used to select which pair of sensors are to
provide the LU and LD signals.
DZ, LU, LD, floor position, and travel pulse sig-
nals are fed as inputs to the microprocessor 74. Thedoor zone DZ, level up LU, and level down LD signals
are also provided through a hardware logic device 78
to a pair of drivers 80, 82 which transmit such
signals to the power unit controller P. The hardware
logic device 78 decodes the levelling and door zone
signals to produce a level signal to the miroprocesor
when the car is level. The device 78 bufEers these
signal~ for the drives 80 and 82.
Signals from the CLC are received in an RS485
receiver 86 over communications link 32, 33, and pro-
vided to an input terminal of the microprocessor 74.
A microprocessor output terminal is connected to the
output driver 84 for providing output to the communi-
cations link 32, 33.
The selector hardware also includes a Reed switch
87, which provides a door zone signal. The Reed
switch 87 signals are provided to a microprocessor
input, and also to the driver 82 for transmission to
the power unit controller. The Reed switch signal is
a duplicate of the door æone signal DZ received from
the sensor 70 and is used as a backup.
Another output of the selector microprocessor 74
provides an output signal "SDI" for slowdown inter-
rupt. This signal, which represents the slowdown
point for the elevator car during a run, is provided
to a driver 88 which transmits the signal to an input
of the CLC.
-13- ~295~
The switch assembly 90 includes a plurality of
switches, which are actuated by cams mounted in the
hoistway indicating that the car is near the top or
bottom of the hoistway. A first switch (terminal
slowdown) activates at slightly less ~1-2 inches) than
the slowdown distance from the terminal floor. A
second switch ~directional limit) actlvates about 1-2
inches beyond the terminal floor. The switch assembly
output signals are provided as an input to the micro-
processor 74, and also routed to the powercontroller P.
The selector of Fig. 4 includes appropriate cir-
cuit protection devices, as well as devices for con-
verting voltages, etc. which are known components and
lS have been omitted for clarity. Also, as indicated on
E'ig. 4, the processor 74 includes an input termina].
for providing an identification code, which is used to
assign an address to the microprocessor for communica-
ting over the communications link 32, 33.
Fig. S is a schematic circuit diagram of the door
operator~ which includes a door operator motor 31 as
shown in Fig. 1. The motor is controlled by an H-
bridge control 100, which includes diagonal pairs o
transistors that are turned on and off selectively,
depending upon the desired output voltage and direc-
tion of rotation.
Fig. Sa illustrates a suitable H-bridge arrange-
ment, containing transistors Dl through D4. By turn-
ing on a diagonal pair of transistors, e.g. Dl and D4,
current flows through the motor armature. By turning
on the other pair of transistors, i.e. D2 and D3,
current flows through the armature in the opposite
direction.
The door operator includes a pair of microproces-
sors, control microprocessor 104 and pulser micro-
processor 106. An example of suitable micro-
processors, that may be used both for the pulser micro
106 and control micro 104, are a pair of Motorola
6~
Model 68701 mlcroprocessors. This microprocessor
includes on-board, programmable memory. In view of
the limited control responsibilities of the two micro-
processors 104, 106, the respective control programs
S can be contained in such on-board programmable memory.
The control microprocessor 104 communicates with the
CLC through an RS485 driver 102 and receiver 102a,
that are connected to serial link 32, 33. A communi-
cations address is assigned to microprocessor using
address jumpers 107.
Pulser microprocessor 106 includes outputs for
supplying control signals BDl through BD4 to a control
logic device 105. Control microprocessor 104 also has
an output connected, through a fre~uency-to-voltage
converter 103, to control logic device 105. The con-
trol logic device buf~ers the signals BDl-BD4 to the
H-bridge 100 and will inhibit them if the voltage from
the converter 103 i9 too low, low voltages being
indicative of improper operation of the
microprocessor.
Control microprocessor 104 monitors for proper
operation of the pulser micro 106 communications over
an 8 bit parallel bus that connects the two micros and
an analog-to-digital converter 109. The control logic
output WDL from control micro 104 is a constant fre-
quency square wave signal that indicates proper opera-
tion of the two microprocessors. The square wave
signal is applied to a frequency-to-voltage converter
103 to change it into a steady state active high logic
signal. If the frequency from 104 is greater than a
preset value, e.g. 400 hz, an active high signal,
CONTROL~ is applied to control logic device 105
to allow the sig,nals BDl-BD4 to be passed through to
the H-bridge control 100 as signals TDl-TD4. If the
signal WDL stops switching or drops below the pre-set
value, the signal CONTROL will ~o low and the bridge
control signals BDl-BD4 will be removed from the H-
bridge.
6~
Any failure that allows the bridge control
signals BDl-BD4 to stop switching properly and be
applied to the bridge steady state will cause the door
to move out of control. Having one micro monitor the
other and using a square wave signal applied to a
frequency to voltage converter provides for a fail
safe watchdog circuit that will activate for either an
active low or active high failure of the micro output.
Motor sensors 101 generate output pulses Pa and
Pb, representative of rotational movement of motor 31,
which are supplied to input terminals of the control
microprocessor 104. Devices for generating output
pulses responsive to motor rotation are known.
The analog-to-digital converter 109 is connected
to a resistor, e.g. 3 ohms in the H-bridge. All motor
current passes through the current sense resistor.
The a/d converter 109 convert~ this current, that
represents torque applied to the door, into a cligital
number. This digital number is made available to both
micros 104 and 106 through the 8 bit parallel bus.
This current feedback is used to limit the maximum
torque of the motor and hence force of the door as
dictated by the elevator code. The value of closing
torque may be preset in the microprocessor, using
the diagnostic terminal 66.
A switch array 108, which is responsive to the
movement of the car door, provides three signals: door
open limit DOL, door closed limit DCL, and door center
travel position CTC. DOL and ~CL signals are provided
to the pulser microprocessor 106. CTC signals are
input to the control microprocessor 104.
The I/O section of the door operator pulser
microprocessor 106 connects the logic section of the
board to peripheral devices, which are the electric
eye, safety edge and gate switch. The pulser micro-
processor 106 can also monitor other signals represen-
tative of the operating condition of the door system
-16- ~2~5~
circuitry, such as monitoring the H-bridge status
through feedback inputs 110.
Fig. 5b shows a door operator housing 150 sup-
porting the door operator motor 31. Motor 31 drives a
first pulley 151 that is interconnected with a main
door pulley 152 coupled to open and close the door, in
a known arrangement. A disc 153, containing slots 154
is attached to the motor shaft 155, and a pair of
magnetic sensors 156 are positioned relative to the
slots 154 to generate pulses representative of motor
rotational displacement.
The housing 150 supports therein printed circuit
board 157 containing the microprocessors 104, 106 and
other circuit components for operating the motor 31.
It also houses bearings 158 for supporting the shaft
159 of the main door pulley 152.
As shown in Fig. 5c, which is a top sectional
view of the housing 150, three bands 160, 161, 162,
each holding a magnet 163, are mounted on a portion of
the shaft 159 of the main door pulley disposed in the
housing 150. The axis of shaft 159 lies in the plane
of the printed circuit board 157, and one edge 164 of
the printed circuit board extends parallel to the
shaft 159. In addition to the other circuit compo-
nents discussed above, three magnetic travel limitsensors 165, 166, 167 are mounted on the board 157
along edge 164, one sensor being mounted opposite each
magnet holder 160, 161, 162. The angular position of
band 160 is adju~ted so that its corresponding magnet
lies opposite to sensor 165 when the door is at the
door open limit. Bands 162 and 161 are likewise
adjusted so that their magnets lie opposite sensors
167 and 166 when the door is at the door closed limit
and at approximate center travel, respectively. The
output of each sensor is connected to a lead in the
printed circuit board to provide the door open limit
DOL, door closed limit DCL, and center travel CTC
-17-
0~0
input signals respectively to the microprocessors 104,
106.
The sensors 165-].67 as well as the sensors 156
used on the motor 31, may be magnetic flux sensors of
known type.
Fig. 6 illustrates schematically one example of
a power controller P which, as shown in Fig. 1, is
located in the machine room adjacent to the pump unit
16. The controller P contains relay logic circuitry
for controlling, responsive to signals from the CLC,
selector and safety circuit, the pump motor starter
200 and four solenoids contained in the hydraulic
valve 18, that regulate the flow of hydraulic fluid to
and from the jack: an "up fast" solenoid 202, and "up
slow" solenoid 204, a "down fast" solenoid 206 and a
"down slow" solenoid 208.
The power controller P is basically divided into
levelling circuits and up and down run circuits. The
levelling circuits include a level enabler LE relay
210, a door zone DZ relay 212, and level up LU and
level down LD reIays 214, 216. LE relay 210 is
enabled by a level signal LE from the CLC. DZ~ LU and
LD relays 212, 214, and 216 are enabled by LU, DZ, and
LD signals from the selector.
The up run circuit includes an up relay 218, a
normally closed car stop interrupt relay 220, a fast
FST relay 222, an up terminal slowdown relay 224, an
top directional limit TOP DL relay 226, and a TMS
(timer-motor-starter) relay 227.
The down run circuit includes a down relay 228, a
car stop CST relay 230, a fast FST relay 232, a down
terminal slowdown DNTSD relay 234, a bottom direc-
tional limit BOT T~ relay 236.
The CLC provides control signals run up ~UM to
enable the up relay 218, fast FST to enable the FST
relays 222, 232, car stop CST to open the normally
closed CST relays 220 and 230, and run down RDM to
~295(~
enable down relay 228. CLC also outputs a viscosity
signal VISC to actuate TMS relay 227.
The power controller P will normally include
interlock relay circuitry, made up of the hoistway
door interlocks, and safety circuitry made up of the
pit safety switch, top and bottom final limits, power
unit stop switch and crosshead stop switch, that pre-
vents the car from executing a run unlder certain con-
ditions, e.g. when the doors are open. Such circuitry
is used in known relay-based systems and is omitted
from Fig. 6 for clarity.
As indicated in Fig. 6, signals from the switch
assembly SW indizative of top directional limit,
bottom directional limit, and up and down terminal
slow down points are fed from the selector to an up
terminal slow down relay 224, a top directional lirnit
relay 226, a down terminal slowdown limit 234, and a
bottom directional limit relay 236. Alternatively,
signals from the switch assembly may be connected to
switches in the power control cixcuit rather than
relay, to act on the circuit directly.
System Operation
Car Loqic Controller
The CLC acts as the central controller for the
system. During all operations except levelling, the
LE signal i9 off and the CLC controls the up and down
run of the power controller.
Referring to Fig. 7a, in operation of the
elevator, hall calls and car calls are inputed lnto
the CLC, which latches the call and provides an output
to the call registered lights. If the doors are open,
the CLC dispatches a close door signal to the door
operator. Once the doors are closed, the C~C then
issues a command to the selector to step up or down.
` 35 Once the step up/down signal is received by the
selector, and the level command is removed, the doox
operator will lock the doors. The selector advances
6~
the target floor to the next floor and transmits the
new target floor to the CLC. If a stop has been
requested at the target floor, the CLC removes tne run
signal. If a stop signal has not been issued, the car
colltinues to run, and the selector issues a late car
refusal signal, at the last chance to stop, to the
CLC. The selector then advances the target floor and
the process is repeated.
If a stop has been requested at the target floor,
the selector sends the interrupt signal SDI at the
slowdown point to the CLC over a separate interrupt
line. As noted above, the normal communlcation
between microprocessors is by way of polled network.
It takes on the order of 200 milliseconds to complete
a poll. However, in the case of the stop signal, the
CLC immediately removes the fast solenoid signal,
disabling the FST relay~ 222, 232. As soon as the car
actuates the level up indicator, the CLC relinquishes
solenoid control to the hardware levelling circuits in
the power controller, by removing the RUM signal and
enabling the ~E relay 210. Final levelling is then
done by the power controller P and levelling sensors.
When the car is level, the selector S issues a
level command to the CLC, and the CLC then permits the
doors to open.
The CLC i5 programmed to retain in memory certain
operating parameters of the elevator system such as
door open times, automatic recall timeouts, fire
servicelandings, etc. Preferrably, the CLC, as well
as the other controls subsystems, also monitor system
operations through the I~O inputs and store elevator
faults when detected. Providing external access, such
as through input 64, permits faults to be read for
troubleshooting purposes, and permits operating para-
meters to be set and modified externally.
During elevator setup and adjustment, certainparameters may be selected and input into the system
for storage. Preferrably such parameters are stored
~Z~ 6l()
in a battery-backed RAM 56 with the battery 57 mounted
on the CLC board. When power fails, or is inten-
tionally turned off, the elevator set~ings wi~l be
retained in the battery backed memory, and when power
is restored, the microprocessor is programmed to look
to this location for operating data. Factory default
settings are stored in the EPROM 54, which settings
also are used for initial elevator setup.
In order to require only one battery, all adjust-
able parameters are sent to the CLC to be saved. TheCLC will upload the parameters on request of the
door/selector via the 485 communications link.
Certain parameters have factory presets or
defaults. On the first power up of the system~ these
parameters will have factory presets until changed.
Also, if new adjustment values are destroyed for any
reason, certain parameters will revert to factory
presets.
Selector
The selector microprocessor includes a program
for retrieving floor height distances and slowdown
distances stored in memory, setting target floors
responsive to CLC commands and movement of the car r Of
determining car distance from the target floor land-
ing, determining direction of elevator travel, and
i~suing slowdown and level signals to the CLC.
During elevator setup, the selector counts dis-
tance pulses between floors during an elevator run and
stores floor height in memory. Also, the slowdown
distance ls input into memory through the portable
diagnostic tool. Other parameters, such as number of
flooræ, are also programmed into memory with the
external diagnostic tool.
Referring to ~ig. 7b, when stopped at floor, the
target floor and the actual position are the same.
The selector checks for level and, if the car is
level, issues a level signal to th~ CLC. When the CLC
-21-
receives a call, for examle an up call, it issues a
step up command to the selector for running up. When
the selector receives this it checks the safeties. If
the safeties are safe, it advances the target 100r,
removes the level signal and issues "fast" FST and
"run up" RUM signals to the CLC. The selector also
retrieves floor height distance from memory, to use as
the initial target distance, and checks the preset
slowdown distance and late call refusal, LCR distance.
As the car moves up, the selector counts pulses to
update target distance, and checks to determine if the
car has reached the late call refusal, LCR distance.
If it has reached LCR for the target floor, the
selector advances the target floor to the next floor
and calculates a new target distance, by adding the
next floor height to the preset target distance. If
it has not reached late call re~usal, the selector
checks the CLC to see if there is still a go up com-
mand. If the go up command has been removed (indica-
ting a stop request at the target floor), the selectorchecks for the slowdown point for the floor. When the
car reaches the slowdown distance, the selector issues
the SDI slowdown command to the CLC and removes the
FST command to the CLC. As the car continues to move
toward the floor (i.e. slowing down), the selector
checks for the door zone signal DZ. When DZ is
reached, it removes the RUM to the CLC and waits for
the car to level to dead level. At dead level, it
issues the level signal to the CL~ and the sequence
starts over. The same sequence takes place for a down
run except, the RUM becomes RDM and the "ups" become
"downs".
During the above sequence, an ISR interrupt can
request the processor to service the pulse count
routine. This routine is very fast and the processor
quickly returns to the above sequence.
The information for slowdown, levelling, and
position is provided by a magnetic tape system. The
-22-
5~
safety and code compliances are provided by switches
mounted on the car and actuated by rail-mounted cams
at the terminal locationsO The selector board moni-
tors all of this and provides the appropriate signals
to the power controller and the CLC.
Preferably, the selector is programmed to self-
correct the set slowdown distance based upon prior
elevator runs. By way of example, during elevator
setup, preferably the installer sets a slowdown dis-
tance value so that the elevator neither overshootsnor undershoots the landing. At such time, the selec-
tor calculates the levelling time under the adjusted
conditions. Thereafter, during elevator runs, should
the levelling time increase or decrease, which is
indicative of changes in viscosity in the hydraulic
fluid, the selector automatically adjusts the slowdown
distance to compensate for the difference in slowdown
time.
Alternatively, the selector can determine the
distance from the landing at which slowdown has been
completed. In the case of overshoot, the selector can
determine the distance from the landing at which the
car has stopped. Should the car undershoot the land-
ing, it will not stop, since the slow solenoid is
still actuated, but will travel in at a minimum speed.
The selector, since it calculates speed, determines
the distance from the landing when the elevator
reaches a predetermined minimum speed, and can make
corrections based thereon.
Door Operator
As noted before, motor current of the door opera-
tor motor 31 is regulated by an H-bridge tr~nsistor
control. In driving the motor, transistor pairs are
turned on and off to provide current to the door
operator motor 31 as a square wave. The duty cycle of
the square wave is increased or decreased to vary the
voltage, and thus the speed of the motor. The pulser
66~
microprocessor 106 controls the operation of the motor
102, by controlling the duty cycle of the square wave
sent by the control logic device 105 to the H-bridge
transistorsO As shown, pulser micro 106 outputs con-
trol signals BDl-BD4, which are converted by control
logic device 105 to corresponding transistor control
signals TDl-TD4. These signals, in turn, are used to
turn on and off transistors Dl-D4. The pulser micro
processor also watches for signals from the safety
edge and electric eye.
~ he control micro 104 tells the pulser micro what
speed the motor should output and which direction the
motor should be going. Information is passed between
two micro's via a bi-directional 8 bit BUS using a
handshake protocol. The control micro also monitors
the speed and current of the motor, adjusting the duty
cycle when necessary. The control micro 104 uses RS-
485 type communication protocol for transmitting and
receiving signals from the CLC.
The H-bridge receives signals BD-l, BD-2, BD-3,
and ~D-4 from the pulser micro, which signals control
the H-bridge. Examples of signals BD-l and BD-4 are
illustrated Fig. 5d. The effective frequency repres-
ents the switching frequency that the armature sees.
Since both transistors BD-l and BD-4 must be on for
current to flow, the effective frequency is twice the
frequency of either transistor. The bridge switching
pattern is designed to allow each transistor to pro-
vide 1/2 the switching required. The combined on duty
cycle applied to the motor is the result of the over-
lapping on periods of both transistors. Therefore the
effective duty cycle applied to the motor is varied by
varying the individual duty cycle of each transistor.
Each transistor is turned on for a variable percentage
of a cycle and then off for the remainder of the
cycle. By operating the transistors out of phase and
alternately, the effective switching frequency is
twice the switching frequency o either transistor.
--24--
J~ i6~
This allows the transistors to switch more slowly,
reducing switching losses in the transistors. More-
over, the effective frequency can be raised to above
the limit of human hearing.
The pulser 106 micro receives 8 bit instructions
from the control microprocessor 104 representative of
the duty cycle required, and a voltage signal repre-
sentative of motor direction.
When the pulser micro receives a new duty cycle
value, it determines whether this duty cycle will be
used to apply power to the door or to retard door
movement ~dynamic braking~. The pulser micro
retrieves from a duty cycle table delay times between
transistor firing sequences for the selected duty
cycle. Then, the pulser micro executes an appropriate
power or retard loop routine to output the appropriate
control signals ~Dl-4, for example as shown in Fig.
5d.
In operating the door, the pulser and control
microprocessors obtain feedback relative to the door
movement. The position of the door and door movement
are provided from a motor sensor. The motor sensor
includes a metal disk with holes and a pair of sensor
units. Each of the sensor units includes a magnet and
a magnetic flux sensor, positioned on opposite sides
of the disk so that the sensor detects the holes. The
disk is connected to the rotor shaft of the motor, so
that the magnetic sensors provide output pulse signals
representative of motor rotation.
Signals from the two sensors are 90 degrees out
of phase. ~hrough a technique called quadrature, as
described further on in connection with the tape
sensor system, the microprocessor can determine the
direction of motor travel. Moreover, the micro-
processor calculates the instantaneous speed of the
motor based on the time between pulses, and conducts
error checking through the two signals. This is done
by the control micro 104.
-25-
During setup of the elevator, the CLC commands
the door operator to execute a set up cycle. At this
command the door operator moves the door from ~he door
open limit to the door close limit and counts the
number of pulses from the motor sensor. Travel dis
tance is stored in the CLC when the door is set-up and
sent to the door on request. The control micro uses
the motor quadrature signal to track the distance
travelled. The position indicator is stored in the
car logic controller in battery backed RAM.
Operation of the door operator is as follows,
with reference to Fig. 7c. Upon receiving a "door
open" command from the CLC, the control micro 104
issues a command to the pulse micro 106 to initiate a
door open cycle.
The pulser micro 106 outputs signals BDl-~D4 in
the proper pattern for open and with the duty cycle to
generate the speed dictated by the control micro 104.
All speeds and positions are retained in the memory of
control micro }04 and the CLC and are programmed
during elevator setup with terminal 66.
The control micro 104 instructs the pulser micro
106 to begin ramping up door open speed at a con-
trolled programmed rate until open high speed is
reached. As the motor rotates, pulse signals PA & PB
from motor sensor 101 are provided to control micro
104~ which decrements the door travel distance, until
it reaches the slowdown point. The control mlcro
instructs the pulser micro 106 to begin ramping down
the door open speed at a controlled rate until the
door reaches a programmed "travel-in" point, where-
after the motor moves at a preset travel-in speed
until reaching the door open llmit. An alternate
slowdown mode is available that applies reversing
power (retard) on the motor until the speed is reduced
to a preset manual speed at which time the door con-
tinues at manual speed until reaching the door open
-26- ~z~
limit. Once the door open limit is reached, pulser
106 stops the motor.
The normal deceleration, as mentioned above, lin-
early decreases the speed from the slowdown point
until the travel-in point. Then the door continues at
manual speed.
The CLC determines the length of time the door
will remain open, which is usually shorter for passen-
gers leaving the car than when passengers are entering
(i.e. shorter when the car is responding to a car call
than a hall call). The CLC issues a "close door"
command. It also instructs the door operator as to
closure mode. The door closes according to the same
algorithm above, except if one of the saEeties is
actuated. Should this occur, the pulser micro 106
reaction depends on the mode of operation. In normal
mode the pulser immediately stops the motor and
reopens the doors. In another mode, the pulser stops
the motor but does not fully reopen the doors. In a
third mode, the pulser ignores the photo-eye and
closes the door under a specified amount of closing
force, i.e. a "nudging" operation. In a fourth mode,
if the door encounters an obstruction that prevents
either complete opening or closing, without activation
of the safety edge or photo eye, the door will open or
close a specified number of times, after which the
cycles will be at increased power. If the doors still
do not shut, the car will shut down. In either event,
the stopping mode is preselected by the CLC, and the
closing cycle is executed independent of the CLC. The
control micro signals the CLC when the doors are
closed and the gate relay is activated.
Power Unit Controller
As discussed above, the power controller com-
prises relay circuitry which is under the control ofthe CLC, except during levelling operations and with
-27-
~Z~
the exception that certain safety devices can override
the CLC control.
In order to make an up run, the CLC issues a run
up command RUM, which actuates the up relay 218, and
also issues a fast signal FST, to activate the FST
relay 222. Under normal operations, the car stop
signal CST is off, and therefore the CST relay 220 is
closed. Also, under normal conditions, the up ter-
minal slowdown switch and up top limit switches are
closed, and therefore relays 224 and 226 are
energized. As a result, the run up and fast signals
from the CLC energize both the up fast solenoid 202
and the up slow solenoid 204, and the car begins a
full speed run up. When the car reaches the slowdown
point for landing, the CLC removes the fast signal,
disabling the up fast solenoid 202, and the car begins
to slow down. As the car approaches the floor, the
selector door æone sensor is actuated by the door zone
magnet, and the selector signals the CLC that the car
is within levelling distance. Thereafter, the CLC
issues the level LE signal, to actuate the LE relay
210, and removes the run up signal RUM. The up relay
218, however~ remains energized, because both the
level up LU and door zone DZ relays 212, 214 are actu-
ated. As soon as the car is level, and the LU signalceases, LU relay is deactivated, deactivating up relay
218 and stopping the car at the landing.
When the up relay 218 i~ activated, an output
signal energizes TMS relay 227, starting the motor.
The TMS functions to keep the pump motor operating
slightly longer than the car is moving, which allows
the car to make a valve-controlled stop and not a
motor starter stop.
When the car is parked at a landing and level,
the door zone relay remains energized. Should the car
move more than a predetermined distance away from the
landing, the selector will issue either a level up LU
signal or level down LD signal, which will activate
-28- ~2~5~
one of the relays 214 or 216, causing the car to level
up or down.
In practice, in order to run up, in addition to
the RUM signal from tha CLC, the interlock relays,
connected to hoistway doors and gate, must be energized
in order to permit the car to move.
A viscosity signal from the microprocessor may
also start the TMS timer and motor starter, in order to
maintain a desired minimum oil temperature. In the
past, it has been necessary to maintain the hydraulic
oil within specified temperature limits to ensure
accurate running of the elevator. In this operation
oil circulates in a bypass mode, being heated in the
process. In an elevator system having a selector that
corrects for changes in oil viscosity~ it is not
necessary to provide a viscosity signal for heating the
oil, except in the case of extreme temperature
variakions, and a considerable amount of energy can be
saved.
If a car is running up and opens the up terminal
slow down, the up terminal slow down switch will
disable the up fast solenoid, permitting the car to run
up only on the slow solenoid. If the car should
thereafter move to the top directional limit, the top
directional limit relay will disable the up slow
solenoid preventing any further upward car movement.
The up and down slow down switches, which are switches
mounted on the car, slow down and stop the elevator
near the top and bottom terminal landings independent
of the salector function.
Selector Construction
Figs. 9-16 illustrate a particularly advantageous
form of a selector system for use in connection with a
microprocessor-based elevator system. Further details
of this construction are disclosed in commonly owned,
co-pending Canadian patent application Ser. No. 556,696
filed January 18, 1988, entitled Elevator System Having
X
-29- ~Zg ~ 6~
An Improved Selector. Referring to Figs. 9 and 10, a
selector tape 300 is mounted vertically in the
hoistway. As an example, the tape 300 may be mounted
on brackets 302 attached to one of the elevator rails
304 at the top and bottom of the hoistway. Preferably,
the tape is made of steel and is approximately 3 inches
wide. The tape 300 includes a series of laterally
elongated holes 306 spaced vertically along the
hoistway. Referring to Fig. 13, two series of magnets
308 and 310 are strategically mounted on the sides of
the holes 306. As described further on, magnet 308
provides a door zone and level indication at each
floor, whereas magnets 310 provide a binary floor code.
The right side is used for levelling; the left for
absolute position (floor code); and the center for
relative position. The slots are preferably punche~d
into the tape in the center thereof.
The tape is preferably a hardened and tempered
steel and supports the strip magnets which are ylued
thereon. It has been found that by using elongated
slots, rather than round holes, the ability to
accurately sense the holes, and provide quadrature (see
Fig. 14, discussed infra) is greatly enhanced.
As shown in Figs. 9 and 10, the bottom of tape 300
is bolted to a bracket 312, which is spring-connected
to a second bracket 314. The second bracket 314 is
then connected to the rail bracket 302. As can be seen
in Figure 10, the tape 300 is provided with slack
between the brackets 312 and 314, to permit a limited
amount of elongation of the spring in the event the
tape binds and is pulled up.
Fig. 12 shows one particularly advantageous
mounting for the selector system in accordance with
the invention. The main selertor housing 320 is con-
nected by a bracket 322 to one of the elevator stiles324. The switch assembly 3~6 is mounte~ by bracket
328 on the elevator stile 324. A first cable 328
X
-30-
connects the switch assembly to the main selector
housing 320 and a second cable 330 connects the
selector to a junction box 333, which in turn is
connected to plug-in terminals on the CLC board.
The switch assembly 326 includes an up terminal
slowdown switch 334, an emergency te~minal speed
limiting switch 334a, a top directional limit switch
336, a bottom terminal slowdown switch 338, and a
bottom directional limit switch 340. Fig. 12 also
illustrates the top directional limit cam 342, which
is mounted by a bracket 344 to the elevator rail 304
in a manner so as to engage, sequentially, the up
slowdown switches 334 and 334a and limit switch 336.
A bottom limit cam of similar configuration is mounted
at the bottom of the hoistway in such a manner as to
engage switch~ 338 and 340. The top o~ the elevator
car is indicated by 344. As can be seen in Fig. 12,
when an elevator is travelling in the upward direc-
tion, up terminal slowdown switches 334 first
encounter the cam 342. As described in connection
with Fig. 6, the siqnals from the switches 334 and
334a are supplied to the power controller, and disable
the up fast solenoid. Accordingly, the car can then
thereafter move in an upward direction only under the
power of the up slow solenoid. If the car continues
to move in the upward direction, the terminal limit
switch 336 engages the cam 342 which disables the up
510w solenoid and prevents any further movement of the
car in the upward direction.
The construction of the main selector housing 320
can best be described in connection with Figs. 11, 15
and 16. Fig. 11 illustrates the housing 320 viewed
from the opposite side of Fig. 12. Fig. 15 is a top
view of the housing, partially in section, without the
selector tape 300. As can be seen in Fig~ 11, the
tape 300 passes through three pairs of opposed guides
322, which are preferably plastic. The preferred
construction of such guides is described further on.
-31~
The main selector housing 3~0 includes, in addition to
the guides, a main sensor board 324 (see Fig. 15) an
auxiliary sensor board 325, an auxiliary sensor ~over
326 and a microprocessor-containing printed circuit
board 328. The sensor board 324 contains magnetic
sensing elements for detecting the strip magnets 308
and 310. The auxiliary sen~or board 325 contains
magnetic sensor elements for detecting the bar magnets
330 when a hole in the tape is in alignment therewith.
The processor board 328 is mounted inside of the
housing 320. The housing 320 i5 preferably formed
from a piece of sheet metal, in which the sides are
bent up to form the sides of the housing 320. The
forming of sheet metal ensures that the portion of the
lS housing 320 that faces the tape will be very ~].at.
E~ig. 16, is a top view of the main sensor board
324 shown in Fig. 15. Preferably the board 324 is
formed of a printed circuit board material, which
inherently is flat and has excellent tolerances. It
is important that the surface on which the detectors
are mounted is extremely flat and in good alignment
with the tape in order to obtain accurate reading. As
shown in Fig. 16, the board 324 has a series of holes
and slots therein for the purpose of mounting. More-
over, the board has a pair of cylindrical bar magnets330 mounted thereon along the center line of the board
and two series of magnetic sensor devices aligned
vertically on either side of the vertical center line.
In particular, one side of the board has five magnetic
sensor devices, preferably hall effect transducers 332
that are vertically aligned relative to strip magnets
310 (Fig. 13). The board 324 also includes a pair of
multiple hall effect sensors 334 and 335, which are
vertically spaced from one another a distance slightly
greater than the length of strip magnet 308 of
Fig. 13. Finally, a pair of door zone hall effect
sensor devices 336 are mounted at approximately a
midway point of sensors 334 and 335.
-32-
The auxiliary sensor board 325 may be of similar
construction to the board 324, i.e., should be rela-
tively flat. A pair of hall effect sensors 33B (one
of which is shown schema~ically in Fig. 15) are
attached to board 325 opposite the magnets 330.
Accordingly, as the selector housing 320 moves rela-
tive to the tape 300, the elongated holes 306 move
between the magnets 330 and their corresponding
sensors 338. Magnets 31a move past the corresponding
set of magnetic sensors 332, and magnets 3Q8 move past
the corresponding magnetic sensors 334, 335 and 336.
In operation, the hall effect devices 338 on the
auxiliary board 325 detect the magnets 330 when the
holes are present and do not detect the magnets
between the holes. The slots are preferably sized to
produce a square wave output from each of the senqors,
and preferably the sensors are spaced from one another
so as to be 90 degrees out of phase, as shown in Fig.
14. These signals are sent to the selector, which
counts the pulses to determine elevator travel dis~
tance. Moreover, as can be seen in Fig. 14 the micro-
processor determines the direction of elevator travel
from the sequence of the signals received. As shown
in Fig. 14, during portions of the elevator travel the
signal from both magnet sensors is zero, for example
at position A. Thereafter r each signal will become
positive, but in opposite sequence depending upon the
direction of elevator travel. By determining the
state of phase B on transition of phase A, the micro-
processor can determine the direction of elevatortravel. (Similarly, the door operator micro uses this
same technique of quadrature to determine the direc-
tion of door motor rotation). The selector reads the
binary floor position sensors whenever the car becomes
level with a landing, i.e. when the door zone sensor
is actuated and the LU and LD sensors are not.
~ loor levelling can be illustrated by Fig. 16
which includes level up sensors 334 and level down
~ ~33~ ~2~
sensors 335. If the car is exactly level with the
floor, magnet 308 (Fig. 13) will be centrally posi-
tioned relative to sensors 334 and 335. Magnet 308
will however energize DZ sensor 336, which represents
the door zone signal. This signal indicates that the
elevator is at the landing and permits the doors to be
opened. At such time as the elevator is not level
with the floor, the magnet 308 will activate sensor
334 or 335, indicating that the car is too high or too
low.
Fig. 16 shows four sensors for the level up and
level down sensor units 334, 335. It is possible to
provide an assembly having only a single sensor at
such a point to provide the level up and level down
signals. In the embodiment shown in Fig. 16, however,
it i9 possible to select which sensors are to be used
for signals. By chanying the sensor connections, the
size of the dead zone can be appropriately varied.
~`'`
