Note: Descriptions are shown in the official language in which they were submitted.
EPS/bt
n1?1Pl237
FEED RATE INDICATIO~I FOR POWER TOOL
DESCRIPTION
BACKGROUMD OF THE Ii~VENTION
This invention is in the fleld of power tools; more
particularly, it relates to a control for indicating loading
based upon loadlng imposed upon the tool by an operator.
In tools that use a moving cutter or cutting edge,
an efficient quality cut requires the establishment of
three parameters, provided proper tool usage techniyues
are followed such as having properly sharpened tools or
utilizing cutting lubricants. The three parameters are,
speed of the cutting edge, material hardness and relative
velocity between the material and the cutter.
In large machine tools, these parameters are taken
into account during a setting up operation for the tool.
The operator will look up the appropriate cutting speed
and material feed in a book of tables supp:lied by the
machine manufacturer, or in a machinist handbook, based
upon the type of material to be machined. Generally, as
material hardness increases, cutter speed and material feed
will decrease. There is a range of volumetric rates of
removal for any given material and cutter which results in
efficient cu-tting, with a good finish. If the cutter speed
is too fast, and/or the feed rate is too slow, the cutter or
material may overheat and over an ex-tended period, dull the
cutting edge. If the cutter is too slow and/or the feed
5 rate too fast, the material tends to be removed in chunks
or pieces, resulting in a poor finish and applying a shock
loading on the power tool which may shorten its life.
Although these principles are well accepted and prac-
ticed in the industry, there has been little done in this
regard in consumer tools, particularly with respect to hand
held or bench power tool.s. For many years, portable tools
such as drills, sabre saws and polishers, and bench tools
such as drill press, band saw, arbor saw, jointer-planer,
sander, for example, have more or less incorporated speed
controls to vary output speed. Ilowever, outside of general
comments about feeding tools or work smoothly, such as
described in user manuals, the judgement about feed rate was
left up to the consumer since there was no way of having
the tool make this decision.
~7hat is required, is an arrangement for a hand held or
bench power tool in which the operator may select the cut-
ting implement size to be used and a material to be operated
upon and have the power tool automatically go to and main-
tain an ideal cutting speed. What is further required, is
some means of indicating to an operator that an ideal feed
rate has been achieved, or alternatively, of accommodating
the power tool to a feed rate se]ected by the operator.
SUrl~l~RY OF TEIE INVENTION
The above improvements are obtained in a hand hel.d or
bench power kool having capability thereon for operator se-
].ection of size of cutting implement such as drill bit, end
mil] or grit for paper~ etc.~ and of material hardness, and
an arrangement which responds to selected cutting implement
size and material hardness to regulate motor speed to an
æ
oytimum va]ue determined Erom a table s-tored in a memory.
The cutting implement may be a cut-ter bit for a router or
a drill bi-t for a drill or may be grit size for a sander.
The arrangement may regulate motor speed to the predeter-
mined optimurm value by monitoring slight changes from theoptimum speed and adjusting effective motor voltage for
speed correction. The effective motor voltage may be varied
by varying the firing angle triggering on a triac in series
with the motor every half line cycle. The longer that the
triac is turned on, the greater the effective motor voltage.
Since the firing angle of the triac is a known quantity,
as is the total applied line voltage, the effective voltage
can be calculated. By dividing the effective voltage by
the effective motor impedance at the optimum operating speed
stored in the memory, the effective motor current is cal-
culated. The effective motor current is directly propor-
tional to motor torque or load. As the feed rate changes,
the motor load changes, resulting in a corresponding current
change which is detected through the triac firing angle
change needed to correct for an attempted speed chanae.
Since the arrangement, which may be a microprocessor
or microcomputer, controls the firing angle of the triac, it
is also able to determine the feed rate for the tool with
data stored in the memory. It is not necessary to go
through the calculations, appropriate current-speed re-
latlonships empirically determined can be converted into
relative triac firing angle data and stored in the memory.
Thus, the arrangement may indicate to an operator the sta-tus
of the present speed rate, or may control the -tool so as to
adjust the cutter speed for the amount of feed rate applied.
A feed rate indication system can be set up utilizing
two vertical rows of LE~s which are visible from the front
of the hand held or bench power tool. The left row corre-
sponds to material hardness selection ranging from soft to
~2~
very hard. The right row indicates typlcal cu-tter size
parameters. r~ith the hand l~eld or bencn power tool con-
nected to a power source, pressing a momentary switch
beneath each row advances -the position of the lit LED from
soft to very hard or from the smallest cutter size indl-
cated to the larges-t indicated. In this way, appropriate
speed selection can be implemented depending on material
and cutter size requirements. Feed rate indication may be
accommodated by, for example, flashing an underfeed indi-
cator LE3 when the power tool is insufficiently loaded, in-
dicating an under feed condition, or by flashing an overfeed
indication LED whenever the power tool is loaded beyond the
rate in which optimum cutting can proceed. ~y keeping both
LEDs continuously lit, or continuously off, the feed rate
lS is indicated as within the preferred limits or range.
Alternatively, ~,EDS may be located within ~n operatorls line
of sight when operating the power tool in a normal fashion.
The over/under feed rate indication system might be used to
train an operator on a scrap piece of material until he has
acquired a feel which will permit him to operate the power
tool with minimum or no reference to the LEDS while wor~ing
on the final piece of work material.
In a power tool in which the feed rate information is
used as a means of changing cutter speed to correct -for
feed rate changes, as the tool is loaded by a feed rate
increase, the motor speed wlll increase; or iE the load
decreases the motor speed would correspondingly decrease. A
program limit would be set to indicate to an operator when
he is at the upper limit of -the speed and Eeed rate range
and possib]y shut down the tool if the warning is ignorecl.
A practical approach might be to start out with a slightly
low speed which would be changed to a higher, normally
regulated speed once a preferred load or feed rate has been
achieved. An upper limit control again would be desirable
as described. If the load is removed from the tool the
speed would, of course, drop to the lower value again.
-
DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, reference
may be had to the specification and the attached drawings
in which:
FIG. 1 is a front perspective view of a power tool in
which the invention has been incorporated;
FIG. 2 is a circuit diagram of the material and cutter
size selection, overfeed and underfeed control according
to the present invention;
FIG. 3 is a cutter size-material~speed ma-trix stored
in the microcomputer shown in FIG. 2;
FIG. 4 is a flow chart outlining the software for the
microcomputer utilized in a preferred embodiment;
FIG. 5 is a detailed flow chart for speed correction
corresponding to varying feed rate load; and,
FTG. 6 is a detailed flow chart for detection and indi-
cation of over and under feed rate.
Referring now to FIG. 1, a hand held power tool, speci-
fically a router 10 is disclosed. The router 10 is fashioned
with substantially cylindrica] housing 12 in the upper end
of which is supported a driving motor (not shown) which is
normally covered by cap ]3. Projecting from the housing 12
are right handgrip 14 and left handgrip 16, there being
visible extending from the right handgrip a trigger switch
lock 15 for a trigger switch (not shown) which is located
in the right handgrip. ~ cord 17 extends from the right
handgrip 1~ to the cap 13 for the motor (not shown), and
line cord 18 e~tends Erom a source of power to the cap and
to an e]ectronic control which will be described below.
Situated approximately midway of the housing 12 is a depth
adjustment ring 20 calibrated as shown to provide for ex-
tension of a cutter (not shown) beneath the router base 22
for operation of the cutter upon a work material. Situated
above the depth adjustment ring 20 is a panel 24 upon which
3~ are inscribed a material table 26 and cutter size table 2~.
~z~
The material table 26 includes the columnar tabulation
"UNDERFEED", "SOFT", "MEDIUM", "H~RD", "VERY HARD"; each
adjacent a circle 30 through 34, respectively, which each
outlines an LED as will be further explained below. The
appellation "SOFT" may apply to white pine; "~DIUM" to
yellow pine, "HARD" to oak or cedar, and ';VERY HARD" to
composite materials such as particle board. Tlle cutter
size table includes a columnar listing "OVERFEFD", "1/4
INCH", "3/8 INCH", "1/2 INCH" and "3/4 INCH"; each also
beside a circle 35 through 39, respectively, which a]so
each outlines LEDs as will be explained below. The material
table 26 is headed by a MATERIAL label which is a pushbutton
27 which may be depressed for a purpose which will be
further explained below. Likewise, the cutter size table
28 is lleaded by a CU~'TER SI~ label which is a pushbut-ton
29 for a purpose to be further described below.
Referring now to FIG. 2, there is shown a block dia-
gram for a circuit which may be included within the cap 13
of the router ]0, preferably adjacent the panel 24 thereof.
The main component in the circuit is a microcomputer 42,
which may be implemen-ted by a PIC1655A manufactured by the
General Instrument Corporation. ~ power supply 44 receives
power from the 115 volt, 60 hertz mains and provides rec-
tified DC voltage for the microcomputer 42, oscillator 46
motor speed detector 64 and firing circuit 68. DC power
is also supplied to LEDs 48 through 51 which are located
in the circles 36 through 39, respectively, of FIG. l; to
LEDs 54 through 57 which are located in circles 31 -through
34, respectively of FIG. l; and to LEDs 52 and 53 which are
30 located in circles 30 and 35 of FIG. 1, respectively. E]ec-
tive scanning from the 1/4" cutter size LED 48 to the 3/4'
cutter size LED 51 is implemented by a cutter size select
switch 60 which is actuated by pushbutton 29 in FIG. 1.
Repeated actuation of the cutter size select switch 60
implements the scanning action through the microcomputer 42
7 9~ 7~:~
,
with the SCanninCJ reverting from the 3/~" cu-t~er size LED
51 back to the 1/4;' cutter size ~,ED ~ so that continual
scanning of the LEDs are possible by repeated actuar,ion of
the cutter size select switch 60. A material select switch
62 actuates through pushbutton 27 of FIG. ]. a similar scan-
ning of the material selection from soft through very hard
and return to soft by the microcomputer 42 in the identical
fashion to the cutter size selection. Selection may be
implemented only when the trigger switch is not depressed,
for the sake of safety.
Another input to the microcomputer 42 is a motor speed
detector 64 which might be implemented by multiple rotating
ma~nets with coil, or by an optical interrupter, used in
conjunction with a rotating segment disc or other device
for feeding back a motor speed to the electronic control.
A preferred method would be to utilize a E~all effect sensor
and a multipole magnet. A zero crossing detector 66
receives a signal along line 67 from the low voltage al.ter-
nating current in the power supply 44 to detect zero
crossing and provide this information to the microcomputer
42 for determination of phase angle for a firing circuit 68
The firing circuit 6~ derives power from the power supply
44 through l.ine 69, and initiates conduction of triac 70
throuyh the gate thereof to provide a ground connection for
25 motor armature 75 and field coils 76 of motor 74. A triy-
ger switch 78 llas a sing].e pole to connect the 115 volts,
60 hertz supply to the field coils 76 and motor armature
75. ~ switch detection circuit ~0 detects closing of trig-
ger switch 7g and signals the microcomputer 42 to initiate
30 operation of tl1e firing circuit 68. ~ l.amp 77 located
ad~acent router base 22 illuminates the work ~rea and is
connected across a field coil to a center tap thereof. The
microcomputer 42 regulates speed depending on the cutter
size selection and material selection selected by means of
switches 60, 62, respectively, and accordin~ to a speed
~3 ~ ~ O ~
table shown in FIG. 3 which may be retained in a read only
mernory (ROM) in the microcompu-ter. The speed of the arma-
ture 75 is detected by the motor speed detector 64, the
signal from which is used by the microcomputer 42 to main-
tain the motox armature at the optimum speed. The motorspeed detector 64 also receives power through line 69.
Speed regulation is accomplished by the microcomputer
42 monitoring slight changes i,n speed from the speed de-
tector 64 and adjusting effective motor voltage for cor-
rection. The triac 70 in series with the, motor is trig-
gered on every half line cycle. The firing angle (that is
the delay time from the start of each half cycle, when the
triac 70 is triggered) will determine the eff~ctive motor
voltage. Since the firing angle of the triac 70 is a
known quantity, as is the total applied line voltage, the
effective voltage can be calculated. By dividing the ef-
fective voltage by the effective motor impedance at the
optimum operating speed, information stored in the ~OM, the
effective motor current is calculated. Motor current is di-
rectly proportiona] to motor torclue or load. As tlle feedrate changes, motor load changes. This results in a corres-
ponding current change and is detected through a change re
quïred in the firing angle of the triac 70 to correct for
' an incipient speed change. The microcomputer 42 controls
the firing angle of the triac 70 by means of the firing cir-
cuit 68. With the da-ta ~hat the microcomputer has stored
in its RO~1, the microcomputer is able to determine the opti-
mum feed rate for the tool. The microcomputer 42 may or may
not ~o through the calculations reEerred to above; however,
the appropriate current-speed relationships can be arrived
at empirically for typica] type of material and cutter
size, and tables oE firing angles for norma] line voltages
and given currents may be stored in the RO~. For various
materials and cutter sizes, for each comblnation of which
there is an optimum speed, power tab],es may also be derived
empirically and related to firinq angle. Thus, -the micro-
computer 42 has means of either indicating to the operator
~L2~
the relative feed ra-te; or of con-trolling motor speed so
as to correct for the feed rate being applied.
When the tool is in use, whichever material and cut~
ter size I,EDS are lit may also be used as feed rate indi-
cators. For example, the selected material LED will flashwhenever the router is insufficiently loaded, indicating an
under feed condition, such as when the router is up to speed
and little or no cutting is taking place. When cutting pro-
ceeds, the material LED Will return to its steady on condi-
tion as the feed rate moves into a preferred current-speed
range. If the feed rate is increased so as to move beyond
the upper limit of the desired feed rate range, the cutter
si~e LED will commence flashing. By keeping both LEDs
steady, the feed rate is within the preferred range. A pre-
ferred method, however, is to have separate LED' S 52, 53which are responsive to underfeed and overfeed, respectively.
Separate LED' s for underfeed and overfeed would allow their
location to be optimized for operator observance while operat-
ing on a work piece. Load tables are established empirical-
ly and stored in the RO~ of microcomputer 42 to just avoidunderfeed for each material and cutter size which causes
the material to begin to disco]or from excess heat, and to
just avoid overfeed for each material and cutter size which
causes material to be removed in chunks resulting in poor
finish. The use of an underfeed lnd;cator wil] have a bene-
ficial effect on the life of -the cutt;ng implement since
overheating thereof will be avoided. The overfeed indicator
will extend both the life of the power too:L and the cutting
implement since by responding to an overfeed indication by
re~ucing loading, shock loading to both the cutting imple-
ment and the power tool may be avoided.
FIG. 4 ls a flow chart of the software for the micro-
computer 92. After insertion of the plug of the power ~ool,
an overload timer which serves to disconnect the motor after
time out of about 5 seconds on a high current overload
o ~
condi.tion to avoi.d destructive motor heating, is reset.
Material and cutter size are se-t to the softest material and
smallest size. ~hereafter a system is implemented -to pre-
vent operation of the power -tool due to a trig~er switch
locked in the on position. With the -tri~ger switch 7~ in
the on position when the plug is inserted, LED's 4~ and 54
corresponding to 1/4" cutter size selection and soft mate-
rial selection may flash at some set rate to alert an oper-
ator that the tool will not further operate until the tri~-
ger switch is shut off. If the trigger switch 78 i.s not inthe on position the microcomputer 42 ls ready to receive a
material or cutter size selection by scanning from soft to
very hard and by scanning from the 1/4 cutter si~e to the
3/4" cutter size upon actua-tion of selector buttons 27, 29,
respectively. If the tri~ger switch 78 is actuated, the
motor 74 is ramped up to speed, and once at that speed
checks the status of feed rate, that is whether an overload
condition e~ists which has initiated the overload timer or
whether an underfeed or overfeed condition exi.sts. If an
overload cond:ition exists, this event may be indicated to
an operator by simultaneous flashing of both the underfeed
and overfeed LED's 52, 53. If an underfeed condition exis-ts
the LED 52 in circle 30 is flashed, and if an overfeed con-
dition exists the LED 53 in circle 3S is flashe~. Without
ar. underfeed or an overfeed condition, -the LEDS 52, 53 will
remain unlit. ~xis-tence of an overload condltion on the
motor 74 ;.nitiates a timer wh;.ch wi.]] time out in 5 seconds
and stop the motor.
FIG. ~ is a detailed flow chart which may be substi.-
tuted between the points A, B in the fl.ow chart ;.n FIG. 4a.in order to obtain a feed rate detection and automatic speed
correction therefor. Definiti.ons for the terms used in the
flow charts of FIGS. 5 and 6 are found in the ~ppendix to
the spec.ification. Feed rate correction operations are
shown ln parallel with Feedback correction operations in
order to prevent the two operations from interfering with
9~2~79Z
each other by givlng s;mul-taneous orders to control the
motor, since on]y one operation can control at a time. The
operations are further dlvidlded lnto parallel paths to
handle increasing and decreasing speed.
In FIG. 5, lt ls first determined if a load change has
occurred which is significant enough to require a feed rate
correction. The third decision box sta-tes the necessity for
determining if the speed change due to a load change is too
large to allow a speed correctlon through a feed rate cor-
rection operation. If so, the feedback operation attempts
-to correct the speed sufficiently to allow the feed rate
operation to take over. This method is used since, for a
feed rate speed correction operation, a decreasing load
should decrease speed while an increasing load should in-
crease the speed. If not careEully controlled by a feed-
back operation, the increasing load could allow the speed
to run away.
It should be noted that once a speed correction under
the feed rate operaticn is achieved, the latest speed be-
comes the reference speed to help to keep future speedcorrections at a minimumO This allows the feedback oper-
ation to regulate to the new speed-feed locatlon rather
than attempting to pull the speed back towards the low
load speed, which would be a lower speed.
It should be noted that in all paths of feed rate cor-
rection or feedback correction, motor speed changes are
achieved through adding or subtracting a small firing angle
g 0 F/(A) x (~ILC)] from the present flring angle
[ 0 PRES] Thls method allows a great deal of flexibillty
with precise contro]. The subscript "F/(~) x (HLC)" refers
to firing per multiples of each half line cycle (EILC).
Thus, lf (A) were set at 5, a change in firlng angle would
occur every fifth llne cycle until the approprlate speed
change was achieved. I-t is likely that the integer ~ulti-
plier will be l for feedback, partlcularly for increasingloads, and 1 or a little higher (2 or 3) for feed rate and
~2
program speed chdnges . D;. ~erent mu1tip~iers ~ight be de-
sired for increasing and clecreasing loads for -the same oper-
ation. Above the resolution limit of the control, the basic
change in firing angle which could be used for different
amounts of phase angle, and consequently speed, changes
within each half line cycle. The various constants such as
the range of no load program speeds covering all program
settings, constant multip]iers and upper and ]ower speed,
firing angle, and current limits as needed are stored in the
permanent memory of the microcomputer ~2. These various
constants may be determined throu~h motor analysis and/or
empirically through tests of prototype products.
In FIG. 6, there is provided a suggested detail flow
chart for insertion between points A and B of FIG. ~a indi-
cating in detail how overfeed and underfeed indication maybe implemented and how feedback correction may also be
imp]emented. Since feed rate cloes not ;nteract wi-th motor
operation, it is placed in series with the feedback oper-
ation. Since the feedback will regula-te the speed fairly
closely with respec-t to the program no load or reference
speed, it is only necessary to determine the upper and lower
firing angles which are the limits for acceptable feed rate
change. Below the minimum firing angle (a fast feed rate)
the overfeed is activated and above the maximum firing angle
the underfeed is activated. For feedback control an initial
decision is made as to whether the speed is be]ow or above
the reference speed; and the fir;ng angle for the triac 70
is increased for below speed, and decreased for above speed.
While the preferred embodiment has been disclosed in
the above descr;p-tion, as well as certa;n rnoclifications
thereto, ;-t wi]l be understood that many more mod;fications
may be made wlthout departing from the scope of the inven-
t;on. For example, ;t w;]l be apparent that ~or certain
power tools which are dedicated to a ]imited use as to mate-
rial and cutter s;ze, no such selection would be required
~7~2~
and indication of an optimum feed condition may be provided.Material selection only may be provided based on a limited
use as to cutter size, ~nd conversely, cutter size selection
only may be provided based on a limited use as to material
selection, with an indication of an op-timum feed condition
provided in either event. Feed rate may be the rate at
which a material is fed through a bench tool, or the rate at
which a power tool moves with respect to the material. In
other words, it is a relative rate between the power tool
and the material. In a sanding power tool, hand held or
bench, the pressure exerted between the material and the
tool becomes a part of feed rate together with speed of the
sanding belt or pad, all of which determines how rast mate-
rial will be removed for a given material and grit size and
type. All of these factors are referable to power demands
made upon a drive motor, and their relationship to power may
be empirically determined and stored in a memory in the
power tool. The scope of the invention is set forth in the
claims below.
,7~2
APPE~DIX
REF Reference speed against which motor speed is
compared to determine whether a speed cor-
rection is required and what speed correction
mode is required.
5 SPRES ~ Current motor speed.
0F Firing angle, angle of sine wave alternating
current at which electronic power switch
(triac) is activated to control motor vo]tage
and thexeby speed.
10 0PR~S Current firing angle
0F/ (L) (HLC) Change in firing angle which occurs
at integer mu]tiples (L or ~l) of each half
line cycle (~LC).
15 L,~ _ Constant mul-~ipliers Aependent on product
function and motor characteristics.
~SL ~ Change in speed from SREF due to load change.
~IN Speed change below which no correction is
required.0 ~SCO~p - Comparison speed change to determine whether
feed rate or feedback correction will operate.
COR Change in motor speed relative to reference
speed.
~SR~Q - Change in motor speed required to correc-t
for current conditions.
