Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to motor-speed controls, and specifically to
a feedback speed-control system for a fluid motor such as that described in,
for example, United States Patent Application Serial No. 13,125, now United
States Patent No. ~ which issued ~ r~e 3~ / 7 ~ / , and assigned to
the same assignee as this application.
Various types of coating material atomizing device drive mechanisms
are known. There are, for example, the drive mechanisms of the following
United States Patents: Juvinall et al, United States Patent 2,759,764;
Juvinall, United States Patent 2,754,226; Simmons, United States Reissue Patent
24,602~ Wirth, United States 3,358,931; Hechenbleikner, United States Patent
1,853,682; and Kent et al, United States Patent 3,011,472q Many coating devices
are known which are adapted to be driven by fluid motors, such as air motors.
There are, for example, the systems of the following United States Patents:
Sigvardsson et al, United States Patent 3~067J949; Wampler et al, United States
Patent 3,121,024; and Allander, United States Patent 2,711,926. The increasing
use of such fluid motors is attributable, in part, to the ease with which the
rotational speeds of atomizing devices driven by such motors can be varied by
varying the fluid pressures to the inputs of such motors.
However, an undesirable characteristic of such fluid motors is that
changes in certain characteristics of coating materials being dispensed from
the atomizing devices coupled to such fluid motors can cause significant vari-
ations in the rotational speeds of such atomizing devices by changing the loads
of such fluid motors~ This is particularly true of very low horsepower (e.g.J
fractional horsepower) fluid motors, such as the turbine-air motor described
in the above-identi-fied United States Patent No.
Generally, such changing characteristics of the coatin~ materials
which are being atomized include changes in viscosities, solids contents,
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specific gravities, and the like, of the coating materials. Unfortunately, in
many situations, for example where color changes are carried out between the
finish coating of successive articles on a production line, the very act of
changing the color of the coating material results in a substantial change in
these characteristics. This occurs simply because it is not always possible
to match every pertinent characteristic of every different coating material
which is being used on the line. This results unavoidably in changes in the
loads on the fluid motors which are atomizing these various coating materials
with many of the changes in coating material color.
As an exampleJ on an automobile finish-coating line, each car to pass
along the finish-coating line will typically be coated with a finish having a
different color from the color applied to the next preceding car, and from the
color to be applied to the next succeeding car. Several systems for controlling
such color changes which take into account, and adjust for, many aspects of
coating material variation from color to color have been proposed.
It is an object of the present invention to provide a system for con-
trolling the speed of a drive motor for an atomizing device associated with
such a production line, with the motor speed being controlled to account for
variations in the characteristics of coating materials which are being atomized
by the atomizing device. With respect to "variations of coating material char-
acteristics" from coating material to coating material, what is meant is that
the load on the motor which drives the atomizing device from which the atomized
coating material is dispensed changes with such coating material characteristic
variations. Accordingly, the motor input must be changed to maintain the motor
speed constant under such changing load conditions.
According to one broad aspect of the present invention, there is pro-
vided a feedback system for controlling the speed of a motor having a motor
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drive signal input, the system including an optical-signal transmitter, an op-
tical-signal receiver, means providing an optical coupler, means for coupling
the optical coupler to the motor in driven engagement, the optical coupler
selectively coupling the optical-transmitter signal to the optical-signal re-
ceiver to provide an optical output signal indicative of motor rotation, means
for converting the optical output signal to a motor drive signal~ and means for
coupling the converter to the motor drive signal input to control motor speed.
According to another broad aspect of the present invention, there is
provided a feedback system for controlling the speed of a fluid motor having
a motor fluid input, the system including an optical-signal transmitter, an op-
tical-signal receiver, means providing an optically sensitive marker, means for
coupling the marker to the motor in driven engagement, the marker selectively
coupling the optical-transmitter signal to the optical-signal receiver to pro-
vide an optical output signal indicative of motor rotation, means for convert-
ing the optical output signal to a fluid signal, and means for coupling the con-
verter to the motor input to control motor speed.
According to an illustrative embodiment of the invention, the means
for coupling the converting means to the motor input includes means for proces-
sing the fluid signal to develop a processed fluid signal. The processed fluid
signal is fed to the motor input.
According to an illustrative embodiment of the invention, the motor
includes an output shaft and the means providing the optically sensitive marker
includes a wheel, the means for coupling the marker to the motor includes means
for mounting the wheel on the motor output shaft, and the wheel further in-
cludes means for providing a pattern on one of its surfaces. The optical-signal
transmitter includes means for directing an optical signal onto the pattern.
The optical-signal receiver includes means for detecting reflections of the
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transmitted optical signal from the pattern ~o provide the optical output signal.
According to an illustrative embodiment, the means for converting the
optical output signal to a fluid signal includes an optical pulse counter for
counting optical-output signals to generate electrical signals indicative of
motor revolutions, a clock for generating a time base, a signal processor, and
means for coupling the optical pulse counter and clock to the signal processor
to generate a signal indicative of motor revolutions per unit time. The con-
verter means further includes means for displaying motor revolutions per unit
time, and means for coupling the display means to the signal processor to pro-
vide a visual indication of motor speed.
Additionally, in an illustrative embodiment, the signal processor in-
cludes a control input for permitting selective adjustment of the motor speed.
Such selective adjustment can be provided either by an analog signal or by a
digital signal, depending upon the specific requirements of the processor. The
illustrative signal processor further includes a comparator for comparing the
signal indicative of motor revolutions per unit time with the control input and
for generating a comparator output signal.
The system further includes means for converting the comparator out-
put signal into the fluid signal and means for coupling the converter to the
comparator. The converter is also coupled to a source of fluid in the illustra-
tive system, the converter acting to convert the comparator output signal to
the fluid signal. In the illustrative system, a fluid-signal amplifier is pro-
vided~ along with means for coupling the fluid-signal amplifier to a source of
driving fluid for the motor, to the fluid-motor input, and to the converter.
The fluid-signal amplifier acts under the influence of the fluid signal from
the converter to control the flo~ of motor driving fluid from the driving fluid
source to the motor input to control motor speed.
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The system may best be understood by referring to the following de-
tailed description and accompanying drawing which is a block and schematic
diagram of a feedback system constructed according to the present invention for
controlling motor speed.
In the drawing~ a fluid motor 10 of the type described in the above-
~identified United States Patent No. ~,27S~ 83 g includes an output shaft 12 uponwhich is mounted an atomizing device 14. Device 14 may be any of several suit-
able types such as, for example, the type described in United States Patent
4,148,932. A feed tube 16 feeds a coating material from a selected one of a
number of sources ~not shown) through a source control (not shown) to the inte-
rior of atomizing device 14, from which the coating material is atomized in a
pattern 18 and deposited onto a target 20, an article to be coated by the mate-
rial. It is to be understood that the target 20 can be moving, for example,
along an assembly line, and that motor 10 need not necessarily be stationary.
That is, motor 10 can be mounted, for example, on a ram associated with a fluid
cylinder which projects the motor 10 and atomizing device 14 into close proximi-
ty to the target 20 before coating material is dispensed. Typically, the sys-
tem also includes a source 24 of electrical potential for electrostatically
charging and aiding in the atomization of particles of coating material in the
pattern 18. In such a system, the target 20 will be maintained at a potential,
here ground 26, to promote migration of the charged particles of coating mate-
rial in pattern 18 toward ~he target 20. This greatly enhances the efficiency
of coating of the target 20 and reduces coating material waste.
A wheel 30 is mounted on the output shaft 12, for example, on the
inside of the motor 10 housing 32, as shown. It is to be understood that wheel
30 need not be a component which is added to motor 10. In fact, the wheel 30
can be the turbine wheel of the motor 10 itself. A marker pattern 36 is pro-
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vided on wheel 30. Pattern 36 includes areas 38, 40 readily distinguishable
from one another by an optical-signal transmit-receive head 42.
Head 42 includes an optical transmitter 44, provided, for example, as
the finished and dressed end of an optical fiber 45 which conducts light from
a light source, and an optical-signal receiver 46 mounted within housing 32 in
close proximity to the finished and dressed end and in an orientation such that
the receiver 46 detects movement of the pattern 36 as areas 38, 40 move beneath
the optical-signal transmit-receive head 42. The pattern 36 can consist simply
of light and dark areas 38, 40, respectivelyJ which, respectively, reflect and
absorb light from transmitter 44 to provide a received ~reflected) signal on
optical receiver 46 once each rotation of shaft 12.
The optical-signal transmit-receive head 42 provides at receiver 46
an output optical-signal which is transmitted along an optical fiber 49 in a
fiber-optic cable 50 coupled to a light source and receiver 52. The cable 50
in the illustrative embodiment includes fiber 45 which transmits light "down"
the cable 50 to transmitter 44, and fiber 49 which transmits received light
"up" cable 50 from receiver 46 to the light source and receiver 52. The head
42 and fiber-optic cable 50 are of a type such as the Spectral Dynamics Fiber-
optic Cable Model 13134-GPT-l available from Spectral Dynamics Corporation of
San Diego, P. 0. Box 671, San Diego, California 92112. ::
Light source and receiver 52 includes electric circuits responsive
to the received light from receiver 46 to generate electrical pulses correspond-ing to the optical output signal from receiver 46. These electrical pulses are
coupled, as shown, through conductors 56 to a clock, or time-base generator 58,
which generates a time base against which occurrences of shaft 12 rotation (as
represented by the signal on conductors 56) are compared. A signal indica-
tive of motor 10 revolutions per unit time results cn conductors 60. The light
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source and receiver 52 and clock 58 are available as a unit in, for example,
the Spectral Dynamics Corporation of San Diego Model 13135. Conductors 60
couple the signal indicative of motor revolutions per unit time to a feedback
comparator and servo drive system 62. The feedback comparator and servo drive
system 62 includes an input 64 coupled by a suitable conductor 66 to a control
input device 68. Device 68 produces an output signal which is selectively vari-
able in accordance with the desired motor 10 speed. The output signal produced
by device 68 on conductor 66 can be either analog or digital, depending upon
the nature of device 68, and the nature and requirements of the feedback com-
parator and servo driver 62. Feedback comparator and servo driver 62 includes
an output 72 which is coupled by conductors 74 to a digital display 76 on which
is displayed shaft 12 rotations per unit time (e.g., r.p.m.). Feedback compara-
tor and servo driver 62, control input device 68, and digital display 76 are of
commercially available types, such as, for example, the Ransburg Corporation
Part Number 20370 Servo Driver; the Beckman 7360 Potentiometer, available from
Beckman Instruments Incorporated, Helipot Division, 2500 Harbor Boulevard,
Fullerton, California 92634; and the Weston 1230 Digital Panel Meter, available
from Weston Instruments Division, Sangamo Weston Incorporated, 614 FrelinghuysenAvenue, Newark, New Jersey 07114, respectively.
An output 78 from the feedback comparator and servo driver 62 is
coupled through conductors 80 to an input 82 of a converter, or transducer 84,
which converts the signal on conductors 80 to a fluid signal at output 88 of
transducer 84. A fluid source, such as a source of compressed air 90, is coupledthrough a conduit 94 to an input 96 of transducer 84. The transducer 84 acts
to convert the signal at input 82 to a fluid signal at output 88 by controlling -
the flow of fluid from source 90 in response to the input signal at 82.
Output signal 88 is supplied ~hrough a conduit 100 to the input 102
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of an on-off solenoid valve 104. The output 106 of valve 104 is coupled through
a conduit 108 to the input 110 of a fluid signal amplifier, or volume booster
112. An additional input 114 of volume booster 112 is coupled through a con-
duit 116 to a source 118 of driving fluid for motor 10. The output 120 of vol-
ume booster 112 is coupled through a conduit 122 to the driving fluid inlet 124
of motor lO.
Transducer 84, solenoid valve 104, and volume booster 112 are o-f com-
mercially available types such as, for example, Fairchild Model 5109 Transducer,
available from Fairchild Industrial Products Division, 1501 Fairchild Drive,
Winston-Salem, North Carolina 27105; Skinner N.C. Solenoid V53DA2020 24VDC
Coil, available from Skinner Electric Valve Division, Skinner Precision Indus-
tries Incorporated, 95 Edgewood Avenue, New Britain, Connecticut 06050; and
Fairchild Model 20 #205103 1:6 Volume Booster, also available from Fairchild
lndustrial Products Division.
The design of the instant invention is advantageous over other types
of feedback control systems for fluid motors in that the element 42 for sensing
motor 10 speed does not come into contact with rotating portionsJ e.g., shaft
12 and wheel 30, of the motor 10. Thus, the system of the present invention
does not consume part of the motor 10 horsepower output to sense motor 10 speed.
Again, this is particularly significant where low- or fractional-horsepower mo-
tors are used to rotate atomizing devices or for other purposes.
Further, by using the fiber-optic cable 50 in the sensing system, it
is possible for the device to operate in a hazardous location (e.g., high sol-
vents content atmosphere) without the need for protective sheathing, insulation,
or the like. Specifically, the fiber-optic cable 50 permits the monitoring and
control of the speed of motor 10, even when the motor 10 is at a high electro-
static potential, e.g., 100 KV, as a result of the action of the electrostatic
potential supply 24.
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