Note: Descriptions are shown in the official language in which they were submitted.
The invention relates generally to a vibratory
feed mechanism, and in particular, to a feed mechanism which
includes an improved amplitude sensing and damping method
and apparatus.
Systems including vibratory feeder bowls are
known for feeding streams of parts or other particulate
material. Such a system typically includes a feeder bowl
coupled to a stationary base by leaf springs. Relative
movement of the bowl and base causes parts within the bowl
to move up an incline spiral path and fall into an accumu-
lating container.
In a typical system parts segregated by a vibratory
feeder bowl are either weighed or counted to collect a batch
of a desired si~e. Once the batch is complete, the parts
are either moved away from the feeder by a conveyor system
or are dumped from a first accumulator to a second receptacle
and then removed.
As an example, three vibratory feeder mechanisms
might be arranged in parallel. A first mechanism would
20 deposit a desired number of bolts onto a conveyor. The
second and third feeder mechanisms would send an identical
number of nuts and washers to the conveyor to be added to
the bolts provided by the first mechanism. In this way
a like number of nuts, bolts and washers will be fed from
individual vibratory mechanisms and com~ined to form a batch
each containing the proper number of parts. Typically they
are then fed to a packaging station.
As the parts are dispensed from the feeder bowl
it is desirable that the amplitude of vibration of the
feeder mechanism remain approximately constant. It is known
that the amplitude of bowl vibration depends upon the mass
6~
of materials within the bowl. As the total mass of the
bowl contents decreases, a reduction in driving po~er is
necessary to maintain a given amplitude of vibration for
the bowl. As the amount of bowl contents increases, the
amplitude of vibration will diminish for a given driving
power. Proposals have been made to sense the amplitude
of vibration of the driven bowl and compensate for changes
in the bowl by varying the power acting upon the bowl.
The objective of such proposals is to maintain relatively
10 constant vibratory amplitude while parts are being fed to
an accumulator.
Prior amplitude sensing techniques have employed
inductive elements mounted to the feeder in close relation
to a magnet which vibrates with the feeder bowl. As the
bowl vibrates, thereby feeding parts in the bowl to a con-
veyor or packaging station, relative motion between the
magnet and an inductor produces an oscillating electrical
signal whose magnitude depends upon the amplitude of vi-
bration. This signal has been used to sense the amplitude
20 and control the driving power to the bowl. At small ampli-
tudes of vibration, however, the signal generated in this
manner was too small to provide an adequate control signal.
A small amplitude of oscillation is particularly
useful in small batch processing where a large amplitude
is inefficient since the feeder is continually being started
and stopped. Thus, prior art amplitude sensing techniques
have been somewhat inadequate when controlling the feeding
of small batches of parts.
Another problem with prior vibratory bowl feeders
30 is that they are characterized by inefficient batch feed
through due to problems encountered stopping vibrations
1~ 6~
when a batch has been completed. Prior systems count the
number or weigh the mass of units fed from the bowl and
seek to terminate the drive power to the bowl when the
proper number or weight of units has been fed. A problem
has been that when the power has been removed from the
driving circuitry, the bowl continues to oscillate or vibrate
for a finite period of time due to its inertia and the res-
toring action of its coupling leaf springs. As the bowl
continues to vibrate, the units within the bowl may continue
10 to be fed from it and accumulate in the container. Thus
undamped oscillation after power termination may send more
than the requisite number of units into an accumulator or
container.
Expressed another way, one problem has been that
prior feeders tend to over feed. Various expedients have
been used to compensate for the over feed problem but the
problem itself has continued.
Some prior art systems have dealt with the over
feed problem by including a diverter into which the excess
20 parts were fed after forced bowl vibrations were terminated.
The excess parts were accumulated and periodically emptied
back into the vibratory feeder bowl. These diverter systems
were inefficient since the excess parts must be continually
returned to the vibratory apparatus and they exhibited other
shortcomings. One such shortcoming was repeated recycling
could cause excessive wear with some parts and another short-
coming was the diverter would not neccessarily provide the
precise flow cut off desired.
A second technique for dealing with the over feed
30 problem was to slow down the oscillations as the requisite
number of parts was neared during the feed process. This
slowing down of the vibration as the correct part number
tj~
was neared resulted in a reduced through put for the system.
Instead of operating at maximum efficiency for the full
cycle for a given batch, the oscillations were slowed as
the proper count was neared. This technique also required
control circuitry to monitor the number of parts in the
accumulator and compare that num~er with the final count
to be achieved.
The present invention obviates the need for a
diverter or other type of over feed compensation and in-
10 cludes an improved amplitude of oscillation sensing technique.The result of these innovations is a maximum through put
of parts. A stopping or braking mechanism of increased
efficiency is provided which applies a damping force to
the feeder's vibratory bowl. The damping force causes the
bowl to stop vibrating more rapidly than prior art systems.
The bowl can be driven close to, maximum speed until the
proper article count or weight has been accumulated. An
increase in efficiency of the order of 40 to 50% can be
achieved when article batches of small quantity are fed
20 by the system. An amplitude control signal is generated
which results in an adequate control signal at all amplitudes
of oscillation and in particular for low level oscillation
used in small batch feeding.
A typical dispensing apparatùs embodying the
present invention includes a drive means for vibrating a
bowl mechanism which in turn imparts motions to a unit or
part to be counted. Apparatus of the present invention
further includes a control circuit which carefully monitors
the amplitude of oscillation and applies a braking force
30 when the vibrating power is turned off.
More particularly, the control circuit includes
a speed control circuit for controlling the amplitude of
t~q~
bowl oscillations. An amplitude sensing circuit which com-
prises a Hall effect transducer is included for monitoring
the bowl oscillations. A power circuit receives a control
signal generated by the combined operation of the amplitude
sensing and the speed control circuit and produces a driving
signal to a bowl coil. Energization and de-energization
of this bowl coil produces movement of the vibratory bowl
due to electromagnetic interaction between a stationary
and moving portion of an electro-magnetic system.
The control circuit also includes a braking control
for reversing the current flow through the bowl coil thereby
reversing the direction of oscillation inducing force applied
to the bowl. This current reversal in conjunction with
a mechanical brake rapidly terminates bowl vibrations and
thereby minimizes the over feed problem.
In a preferred embodiment, the braking control
sends a timed braking signal to the power circuitry after
a desired number of parts have been dispensed from the bowl.
This signal causes the bowl to be driven but in a timing
sequence which disrupts the original oscillations. The
braking circuit causes a reversal in bowl coil current for
a time period long enough to damp vibrations but not so
long that the reverse bowl current again drives the bowl
into vibration.
The power circuit of the preferred embodiment
includes controlled rectifiers for sending power signals
to the bowl coil. A gating signal allows current to flow
in these controlled rectifiers in response to control signals
from the speed control and braking control circuitry. When
30 the bowl is driven during normal feed operation, a first
controlled rectifier is periodically rendered conductive
in response to signals from the speed control circuit.
6~1~
When controlled braking is to be applied, a second controlled
rectifier in the power circuit is rendered conductive.
A comparator which has one input connected to
the amplitude sensing circuit and a second input connected
to a reference voltage insures that the braking signals
are applied for an appropriate time period. When the action
of the reversed bowl current reduces the amplitude of oscil-
lation, the input from the amplitude sensing circuit becomes
less than the reference input and the second controlled
10 rectifier in the power circuit is rendered non-conductive.
At the same time the second controlled rectifier
is rendered conductive, the mechanical brake is activated
to enhance bowl braking. In the preferred embodiment of
the invention the mechanical brake includes a coil which
when energized causes a bowl support to be attracted toward
and come in contact with a bowl base structure. The mechani-
cal brake is slower acting than the braking action achieved
by current reversal through the drive coil so by the time
physical contact is made bowl vibration has already been
20 significantly damped. This difference in speed between
the two braking actions diminishes wear on the mechanical
brake. Were it not for the mechanical brake, it is possible
that reversed bowl current through the second controlled
rectifier would not only disrupt the bowl rhythm but begin
to affirmatively drive the bowl through reverse bowl coil
energization.
From the above it is apparent that one important
feature and object of the present invention is to provide
a damping or braking force to a driven vibratory feeder
30 mechanism. In this way a more efficient counting mechanism
is provided without the use of diverter or other excess
unit compensation techniques. The system vibrates at a
i6~
constant frequency of oscillation throughout its batch pro-
cessing and is rapidly stopped by a combined mechanical
and electrical brake after a batch of parts has been dispen-
sed.
A further objective is an amplitude sensing circuit
which accurately transmits amplitude data to the power cir-
cuit. This improved amplitude sensing is more accurately
representative of the amplitude than prior art amplitude
sensing techniques. These and other features and objects
10 of the invention will be better understood when considered
in conjunction with the detailed description of the invention
and the accompanying drawings.
Figure 1 is a side view of material handling appa-
ratus embodying the present invention.
Figure 2 is a top plan view of a vibratory feeder
bowl.
Figure 3 is a side plan view of the bowl illustra-
ted in Figure 2.
Figurè 4 is a side view depicting a mounting
20 mechanism for the feeder bowl.
Figure S is a top plan view of the mechanism of
Figure 4.
Figure 6 is a schematic of a control circuit for
controlling the vibration of the feeder bowl.
Figure 7 is a more detailed schematic of the control
circuit shown in Figure 6.
Figures 8A-8C show voltage waveforms at certain
locations of the control circuit of Figure 7.
Figure 9 shows voltages across a bowl drive coil
30 as the bowl is both driven and stopped.
Referring to FIG. 1, a material dispensing appara-
tus using the preferred embodiment of the present invention
G~3
is indicated generally by the numeral 10. The ~pparatus
10 is operative to dispense articles, such as pills,
washers, screws, or other small items into a container
12 positioned next to the article handling apparatus
10 .
The apparatus 10 inclùdes a base structure
14 which supports a supply hopper 16, and a vibratory
feeder 18. The vibratory feeder 18 includes a feeder
hopper or bowl 20 which deposits the units into the con-
tainer 12. In operation, articles to be dispensed areloaded into the supply hopper 16. The material dispensing
apparatus then feeds controlled amounts of articles from
the supply hopper 16 into the feeder 18. Vibratory motion
of the feeder causes -the articles to move from the feeder
18 into the accumulator bucket or container 12. A limit
switch assembly ~not shown) maintains a predetermined
amount of articles in the feeder 18 by controlling article
movement from the supply 16 to the feeder 18.
The operation of the vibratory feeder can be
controlled by an external signal from a counting unit
22. This signal will automatically control the dispensing
of a predetermined amount or weight of articles into
the accumulator or container 12. After the required
number of articles have been accumulated, the article
dispensing apparatus 18 is turned off and motion ended
by means of the braking system embodied by the present
invention.
Referring now specifically to Figures 2~5, it is
shown how the present apparatus produces a vibratory move-
ment to propel articles to be accumulated along a spiral
path in the bowl 20. More specifically, FIGS. 2 and 3 depict
a vibratory feeder bowl 20 used for accumulating the parts
to be counted once they are dumped from the feeder hopper 16.
The parts are deposited in the bowl 20 and are caused to
vibrate in a spiral path 24 until they reach the end of
that path and are dumped from the vibratory bowl into the
container 12. As seen in FIGS. 2 and 3 the vibratory bowl
includes four flange elements 26 spaced at well defined
locations about the periphery of the feeder bowl. Each
of these flanges includes a threaded aperture 28 for receiv-
ing a connector which mounts the vibrating bowl to an oscil-
lating arm 44 (see FIGS. 4 and 5). In this way, the vibratory
bowl is suspended from the arms and, as will be seen with
reference to FIGS. 4 and 5, can be caused to oscillate to
create movement in the parts along the bowl's path 24.
Referring now to FIGS. 4 and 5, apparatus for
oscillating the bowl is referred to generally by reference
numeral 40. This apparatus 40 includes a massive supporting
frame element 42 and a much lighter suspended element 43
including the arms 44 which extend generally radially.
The radially extending arms 44 include apertures which align
with the apertures 28 in the flanges 26. Bolts, not shown,
threaded into the apertures 28 join the vibratory bowl with
the radially extending arms. The element 42 is suspended
from the frame of the dispenser 10 by bolts 45 which thread
into apertures in the frame element 42.
The suspended element 43 is suspended from the
support element 42 by means of flexible leaf springs 46.
As seen in FIG. 4, the leaf springs are attached to the
support element 42 and suspended element 43 by means of
suitable connectors which in a preferred embodiment comprise
a threaded bolt arrangement. The leaf springs 46 are angled
with respect to the vertical in such a way that relative
vertical motion between the radially extending arms 44 and
the support element 42 will produce a circular oscillatory
movement of the radially extending arms and the attached
bowl.
Relative vertical motion between the support element
42 and the arms 44 is achieved by means of an electromagnetic
motor which utilizes conventional I and E laminations.
The E laminations are mounted to the supporting element
and the I laminations to the radially extending arms. Ener-
gization of the E laminations causes a relative motion due
to the changing flux which energization produces. This
flux interacts with the I laminations causing electromagnetic
forces to be created between the two halves of the motor.
These forces cause the radially extending arms to move ver-
tically relative to the supporting element 42. This motion
is caused by the attraction of the I laminations to the
field produced in the E laminations.
Due to the angled mounting of the leaf springs 46,
the vertical movement caused by the electromagnetic inter-
action becomes a combined, relatively slow, circular and
vertical movement. When the magnet is deenergized, energy
stored in the springs rather suddenly drives the bowl down
and in the opposite circular direction. Inertia of parts
along the spiral bowl ramp causes them to "climb" the ramp
when the bowl is spring driven. This climbing causes the
parts located within the bowl to move along the spiral bowl
ramp and drop into the accumulating container shown in FIG. 1.
A mechanical brake 50 is connected to the support
element 42. Mounted to one of the radially extending arms
i66~
44 beneath the bra~e 50 is a wear element 52. Inside the
brake 50 is mounted a brake coil 53 (Figure 7) which when
energized attracts the wear element causing a brake surface
54 to contact a wear surface 55. This braking in combination
with a current reversal in a bowl coil 110 which wraps around
the E laminations of the electro-magnet brings the bowl
20 to a stop after a desired number of parts have been fed
into the container 12.
During the fèed operation, oscillatory forces
are applied to the bowl by alternate energization of the
electromagnet. During the energization, current passes
through the bowl coil 110. The resultant electromagnetic
force between the I and E laminations reduces the distance
between the base and radial arms. When current is removed
from the bowl coil, the restoring action of gravity and
the leaf springs increase the gap between the base and arms.
The cyclical energization and de-energization of the coil
results in up and down oscillatory movement which inputs
spiralling oscillations to the bowl.
The bowl oscillations and braking are controlled
by a circuit 112 schematically illustrated in FIG. 6. One
aspect of this circuit is the modulation of the amplitude
of oscillation in response to the weight of parts carried
by the vibratory bowl. When the bowl is relatively full,
more power must be supplied to the electromagnetic motor
to achieve the same amplitude of vibration. A second aspect
of the disclosed circuit is to provide braking action to
the bowl when an appropriate number of parts have been dis-
pensed. Were it not for this braking, the vibratory bowl
would continue to oscillate with a natural undamped frequency
which would cause excess parts to be dispensed. This cause
of inaccuracy has substantially been eliminated by means
11
iG~q~
of the unique and novel-braking technique.
The control circuit 112 comprises a power circuit
114 which allows current to flow through the bowl coil 110.
The coil 110 is driven by a source of energy 113 which in
one embodiment comprises a 120 volt alternating current
source of 60 cycles per second. Since the bowl coil 110
wraps around the magnet's E laminations, energization and
de-energization of the coil 110 causes the bowl 20 to vibrate -
due to the mechanical~structure of the bowl support. As
described hereinafter the power circuit 114 controls the
timing and direction of current flow through this bowl coil.
The control circuit 112 further includes a speed
control circuit 116, an amplitude sensing circuit 118, and
a counter or switch-120 which in combination control energi-
zation of the bowl and brake coils 110, 53. The amplitude
sensing circuit 118 and speed control circuit 116 are con-
nected and combine to generate an output 122 proportional
to both a desired amplitude of vibration and the actual
amplitude of vibration of the bowl feeder. This output
20, 122 is compared to a sawtooth voltage signal by a comparator
124 which produces an input 126 to the power circuit 114.
The status of this input 126 determines the amount of power
transmitted through the bowl coil 110 by the power circuit
114. The amplitude sensing circuit 118 includes a Hall
magnetic transducer 128 (See Figure 7) which provides an
oscillating signal proportional to the amplitude of oscilla-
tion imparted to the bowl mechanism. In this way, a feed
back signal dependent on the amplitude of feeder oscillation
is combined with a speed control signal dependent on desired
amplitude of oscillation.
The comparator 124 selectivel~ renders conductive
a switching means such as a silicon control rectifier 130
12
6~
(See Figure 7~ within the power circuit 114. When the sili-
con control rectifier is rendered conductive, it allows
the alternating current source 113 to drive the bowl coil
110 for a controlled time period. The control from the
speed control circuit 116 is modified in response to the
amplitude of vibration as sensed by the Hall effect trans-
ducer 128. As a result, a combined speed and amplitude
control technique is achieved for controlling the amount
.
of power sent to the bowl coil 110.
A second comparator 132 deactivates signals from
the first comparator 124 by controlling a second input 134
to the power circuit 114. When a stop control input 136
to the second comparator 132 drops in response to a parts
counter or switch, the driven oscillation of the bowl is
terminated.
To damp continuing oscillations, a third comparator
138 produces a signal on a third input 140 to the power
circuit 114 causing alternating current to pass through
the bowl coil 110 but in a direction opposite to the direction
of current flow during normal bowl oscillation. This rever-
sing of bowl coil current flow causes the bowl to be damped
much more quickly than it would if the power were merely
removed from the coil. The reverse current signal is main-
tained for enough oscillations to damp the bowl mechanism.
A fourth comparator 142 energizes the brake coil 53 of the
mechanical brake 50. The mechanical brake 50 is slower
acting than the disruption achieved by current reversal
in the bowl coil 110 but clamps the relatively moving bowl
20 and support 42 to avoid any possibility that the bowl
20 may be overdriven by the reverse bowl coil current.
A detailed schematic of the control circuit 112
is illustrated in FIG. 7. Unless otherwise noted, all
13
` 11~i~6s~
resistors are 1/4 watt resistors and all capacitors are
indlcated in micro farads. Many of the elements within
the circuitry are chosen for convenience but it should be
appreciated to those skilled in the art that certain design
modifications could be made in the resistor or capacitor
values without departing from the spirit of the invention.
As seen in FIG. 7, current flow through the bowl
coil 110 is controlled by two silicon control rectifiers
.
130, 131. Depending on the conduction states of these two
rectifiers, current can flow through the bowl from the 120
volt source in one of two directions. During normal vibra-
tory operation (i.e., when parts are to be moved along the
spiral ramp) a drive SCR 130 will allow conduction through
the bowl in one direction. The other SCR 131, which will
be referred to as a braking SCR, is rendered nonconductive
so the bowl coil will be energized during only a maximum
of one half the alternating current cycle. During the half
cycle the drive SCR may not conduct, the bowl will be driven
in an opposed direction by the combined action of the leaf
20 springs and gravity as noted previously.
When the requisite number of parts have been accu-
mulated or the proper weight of parts dispensed, the drive
SCR 130 is rendered nonconductive and the brake SCR 131
is rendered conductive for a brief period of time to dyna-
mically brake the bowl by allowing a back current to flow
through the bowl coil in a direction opposite to its part
feed flow. This back current disrupts the rhythm of oscil-
lations produced by action of the drive SCR 130 and quickly
brakes the bowl. No excess units or parts are dispensed
30 by continued vibration of the bowl and unlike some prior
art systems during the bowl drive portion uniform frequency
and amplitude of bowl oscillation is maintained.
Gating inputs 142~ 144 to the two SCR's 130r 131
are connected to a pair of optically coupled SCR's 146~
148. When these optically coupled SCR's conduct r gating
signals are sent to the SCR's 130r 131. The gate connection
is achieved through filter circuits 150 which suppress tran-
sient signals from reaching the SCR gates 142r 144.
The optically coupled SCR's 146r 148 provide a
signal to a connected one of the gates 142 r 144 in response
to the voltage on three inputs 126~ 134r 140 to the power
circuit 114. One optically coupled SCR 146 will conduct
whenever a first input 126 is greater than the second input
134. The second optically coupled SCR 148 will conduct
and therefore turn on the brake SCR 131 whenever the second
input 134 is greater than the third input 140. It is control
of the three inputs which determine how the vibratory bowl
is driven and damped.
The second comparator amplifier 132 transmits
its input 134 midway between the two optically coupled SCR's
146r 148. During normal powered operation of the vibratory
20 bowl, this input 134 is maintained at a low or ground poten-
tial. This state is achieved through control of the ampli-
fier's two inputs 152~ 154. A first input 152 is maintained
at a reference voltage of about 5 volts by a voltage divider
156 and a 10 volt power source 158. A second input 154
is maintained in an approximately 10 volt level due to con-
nection to a second voltage divider 160 and a 12 volt control
input 162 from the parts counter 22. During normal feed
operation of the system, the 12 volt control input and voltage
divider 160 maintains the input 154 to the second amplifier
30 132 at a value of approximately 10 volts. When this input
is compared to the 5 volt input on the other input 152,
a low or ground output 134 is sent to the connection between
;ti66~
the two optically coupled SCR's 146, 148.
The control input 162 from the counter 120 drops
to about one volt when a desired number of parts have been
fed from the bowl 20 into the container. When the control
input 162 drops below 5 volts, the forced vibration of the
bowl is stopped due to the change in output by the second
amplifier 132. When the input 154 is compared to the positive
5 volt voltage on the other input 152, the output 134 changes
from its low ground state to its high state. In this con-
10 figuration, no current may pass through the optically coupledSCR 146 which as a result sends no gating signals to the
bowl drive SCR 130. Thus, when the control input 162 is
low the bowl drive SCR 130 is maintained in a nonconducting
state and the bowl drive vibrations are removed. Although
in the preferred and disclosed embodiment a counter 22 gen-
erates the control input 162 it should be appreciated that
a simple on/off switch could also be used to lower the input
154 thereby rendering the drive SCR 130 non-conducting.
When the control input 162 is high, i.e. parts
20 are being fed, the optically coupled SCR 146 may or may
not conduct depending on the state of a second input 126
to the power circuit. With the input 134 low, the optically
coupled SCR 146 conducts so long as the input 126 from the
- first or drive bowl comparator 124 is in a high or positive
state. In this configuration, power will flow through the
optically coupled SCR 146 sending a gating signal to the
drive bowl SCR 130.
The comparator 124 which generates the signal
126 to the optically coupled SCR 146 has two inputs 166,
30 168 the relative size of which dictate whether the optically
coupled SCR 146 conducts. A first input 166 transmits a
reference signal which is a sawtoothed waveform. A 120 volt
16
i66~
alternating current 113 is shaped into a sawtooth waveform
by a sawtooth generator 170 to Eorm this waveform.
The second input 168 to the comparator 124 trans-
mits a signal generated by the combined action of the ampli-
tude sensing circuit 118 and the speed control circuit 116.
When the input 166 from the sawtooth generator is greater
than the input 168, the output 126 from the comparator 124
will be high and current may pass through the optically
coupled SCR 146. Conversely, when the input from the sawtooth
generator is lower than the input 168 the output 126 will
be low and the optically coupled SCR will not conduct.
Thus, when the sawtooth waveform reaches a voltage above
the waveform from the combined action of the amplitude sensing
and speed control circuitry the optically coupled SCR sends
a gating signal to the bowl drive 130 rendering that bowl
drive SCR conductive. When this occurs a 120 volt alternating
current source 113 energizes the bowl coil 110 causing bowl
vibration.
The amplitude sensing circuit 118 comprises the
Hall effect transducer 128 mounted to the support 42 in
spaced relation to a magnet 174 (Figure 4) mounted to one
of the radially extending support arms 44. The Hall effect
transducer 128 is energized by an input 176 coupled to the
10 volt source 158. A second input 178 is grounded. The
10 volt source 158 causes current to flow through the Hall
effect transducer 128 which is modulated by the magnetic
field in the vicinity of the magnet 174. As relative motion
occurs between the magnet 174 and the transducer 128 an
oscillating voltage output appears at two outputs 180, 182
from the Hall effect device 128.
These outputs 180, 182 are coupled to a differential
amplifier 184 having an output 186 proportional to the voltage
17
66~
difference between the two outputs 180, 182. As the ampli-
tude of bowl vibration increases the average voltage dif-
ference between these two outputs 180, 182 increases and
therefore the differential amplifier output 186 is a measure
of bowl amplitude of vibration.
After passing through a coupling capacitor 188
the differential amplifier output 186 is combined with an
output 190 from the speed control circuit 116. I'his output
.
190 adds to the output 186 from the differential amplifier
184 and produces an input signal 191 to a comparator ampli-
fier 193. The input 191 is thus related to both sensed
amplitude of vibration and desired amplitude of vibration.
The speed control circuit 116 comprises two tapped
variable resistors 192, 194 coupled to a twelve and ten
volt sources respectively. The variable resistors 192,
194 are adjustable by the user to selectively tap the two
voltage sources and generate two voltage inputs 196, 198
to a differential amplifier 210. The amplifier 210 subtracts
the signal at its non-inverting input 196 from its inverting
20 input 198. ~y adjusting these two inputs it is possible
to generate an output 190 proportional to a desired amplitude
of vibration for the feeder bowl. Once the output 190 from
the speed control circuit 116 and the output 186 from the
differential amplifier 184 are combined at a junction 211
the combined signal is transmitted to the comparator 193.
This comparator 193 generates a pulsating waveform which
is smoothed by a resistor 214 and capacitor 216 acting as
an integrator. The signal 168 therefore has a level related
to both desired and actual amplitude of bowl vibration.
~rom the above it should be apparent that the
input 168 to the comparator 124 is a signal whose size depends
not only on a desired speed or amplitude of the oscillation
18
ti60
but also on the actual amplitude of oscillation as measured
by the Hall transducer 128. Modifications of the signal
168 therefore occur in response to changes in the load in
the feeder bowl as well as to changes introduced by the
user through modification of the two speed control inputs
196, 198. In this way an amplitude sensing controi is em-
ployed which accurately produces a control signal 168 depen-
dent upon the amplitude of vibration even for small amplitudes
which posed a problem for prior art amplitude sensing cir-
10 cuitry.
The comparator 124 compares its two input signals,166, 168 and produces an output 126. As noted previously,
the comparator is configured such that when the input 166
from the sawtooth generator 170 is greater than the input
168, the output 126 from the comparator will be high and
current may pass through the optically coupled SCR 146.
Conversely, whenever the input 166 is lower than the input
168, the output 126 will be low and the optically coupled
SCR 146 will not conduct. Thus when the sawtoothed waveform
20 reaches a voltage above the waveform from the combined action
of the amplitude sensing and speed control 124, the compara-
tor 124 produces a high level output and the optically coupled
SCR 146 sends a gating signal to the bowl drive SCR 130.
This gating signal renders the bowl drive SCR 130 conductive
so the 120 volt alternating current source 113 energizes
the bowl coil 110 and vibrates the bowl.
When the sawtoothed waveform drops below the signal
168, the comparator 124 produces a low output and the opti-
cally coupled SCR is turned off. The gating signal to the
30 bowl drive SCR 130 stops and the 120 volt alternating current
source 113 no longer energizes the bowl coil 110. The effect
of the comparison made by the comparator 124 is to render
19
l~tjti6~D
conductive the optically coupled SCR 138 during selective
portions of the sawtooth waveform. Thus, if the sawtooth
168 is greater than the signal 168 for only a small portion
of the alternating current cycle, the bowl coil 110 will
be energized for a short time and little power applied to
the bowl. If the sawtooth signal 166 exceeds the amplitude
and speed control signal 168 for a greater portion of the
cycle, more power drives the feeder bowl.
As the load within the bowl changes, the portion
of the AC cycle during which the bowl coil is energized
varies to maintain constant amplitude vibrations. When
a large number of parts are dumped from the supply hopper
16 to the vibratory bowl 20, the bowl must be driven with
more power to achieve constant amplitude oscillation. This
is achieved since the output 186 from the amplitude sensing
circuit is lowered and the sawtooth waveform is greater
than the signal 168 for a longer time period which renders
the optically coupled SCR 146 conductive for a longer time
period. As this greater power achieves a larger amplitude,
the amplitude circuit output 186 again increases and the
time of conduction again decreases until a uniform amplitude
of oscillation is achieved.
Figures 8A-8C show waveform diagrams for the two
comparator inputs 166, 168 and the output 126 for two differ-
ent amplitudes of bowl vibration. The vertical coordinate
indicates signal size and the horizontal coordinate is time.
The solid line represents waveforms for a .10 inch amplitude
of bowl vibration and the dotted line represents a .05 inch
amplitude.
As noted the input 166 (8A) is a sawtooth waveform
and the input 168 t8C) is dependent on the amplitude of
s)
vibration. The output 126 (8B) is seen to be "high" for
a longer time period for the larger amplitude of vibration,
indicating the bowl coil 110 is driven for a greater portion
of the alternating current cycle when a larger amplitude
vibration is desired.
When the control voltage 162 goes low, the first
optically coupled SCR 146 stops gating the drive SCR 130
and the power circuit 114 affirmatively damps the bowl vi-
brations. To achieve this damping, a braking SCR 131 allows
current to flow through the bowl coil 110 in a direction
opposed to the positive bowl drive. When the brake SCR
131 is rendered conductive, therefore, a signal passes through
the bowl coil 110 which sets up electromagnetic interactions
between the I and E laminations and damps motion of the
feeder bowl 20.
The state of the output 140 from the third compara-
tor 138 determines how long this reverse current passes
through the bowl coil 110. Once the control voltage 162
goes low, the output 134 from the comparator 132 remains
20 high until bowl vibrations are again initiated. Thus, the
SCR 131 will be gated by the optically coupled SCR 148 so
long as the output 140 from the comparator 138 is low.
The state of the output 140 is determined by two
inputs 220, 222. A first input 220 is coupled to the output
186 from the amplitude sensing circuit 118 through a gain
of 47 amplifier 224. The signal appearing at this input
220 is an oscillating signal 47 times larger than the oscil-
lating signal 186 from the differential amplifier 184.
A second input 222 is coupled to a voltage divider 226 and
30 the output from a comparator amplifier 230. When bowl vibra-
tions are to be stopped, the output from the comparator
6~
230 is initially low so that the input 222 is maintained
at a value of approximately 1 volt by action of the voltage
divider 226 coupled to a 10 volt source 158. The input
220 is an oscillating signal which causes the comparator
138 to generate a low output when greater than the input
222 and a high output when it is less than the input 222.
As the Hall device 128 oscillates in relation to the magnet
174, the output 140 oscillates on and off causing the SCR
148 to send gating signals to the SCR 131. The SCR 131
reverse drives the bowl coil 110 whenever it is gated into
an on condition and the amplitude of vibration rapidly de-
creases. As the amplitude of vibrations decreases, the
Hall device generates smaller signals until the input 220
becomes less than the 1 volt input maintained on the input
222. When this occurs the comparator 138 generates a constant
high level output 140 thereby turning off the SCR 131~
As the amplitude of vibration decreases due to
the dynamic braking action of the SCR 131, the gating signals
on the gating input 144 remain high for less time per bowl
vibration. Thus, initially the SCR 131 conducts for essen-
tially a complete half cycle of the source 113. As amplitude
of vibration decreases the SCR 131 is gated into conduction
later in the cycle. As noted previously when the input
220 from the Hall transducer 128 falls below 1 volt all
gating signals cease.
Figure 9 shows the change in voltage across the
bowl coil 110 as damping occurs. Initially the coil 110
is shown driven by the source 113. The power applied to
the bowl is moderate since the on time of the drive SCR
130 is substantially less than an entire half cycle. At
a point 223 the counter input 162 goes low and dyr,amic braking
begins. The brake SCR 131 is rendered conductive and the
22
6~
source 113 disrupts motion by reversing the current through
the coil 110 by driving it out of phase with the rhythm
set by the drive SCR 130. Initially this reverse current
is applied for essentially an entire half cycle. As the
amplitude diminishes, however, the input 220 is greater
than the input 222 for less time and therefore the braking
power decreases.
The comparator 230 provides a mechanism whereby
dynamic braking action by the SCR 131 is maintained for
only a limited amount of time. A first input 232 to the
comparator 230 is coupled to the stop control input 162
from the counter. When an appropriate number of parts have
been dispensed from the bowl 20 this line goes low causing
the input 232 to also go low. Due to the action of a resis-
tor 233 and capacitor 235, however, a time delay of approxi-
mately 200 milliseconds is experienced before the input
232 goes low in response to the control input 162. A second
input 234 to the comparator 230 is coupled to a voltage
divider 236 which maintains the input 234 at a value of
~lightly less than 2 volts. After a time delay of approxi-
mately 200 milliseconds, therefore, the comparator 230 changes
states generating a high output to the input 222 on the
comparator 138. This high output 222 when compared to the
oscillating signal from the Hall transducer 128 will insure
that the output 140 is high and that the brake SCR 131 is
disabled. This safety mechanism prevents the brake SCR
131 from continuing to conduct. If allowed to do so current
flow through the SCR 131 might not only disrupt oscillations
and damp motion but begin to drive the bowl 20 causing parts
to be dispensed.
23
i6t~
After the dynamic braking caused by gating the
brake SCR 131 has reduced bowl motion the mechanical brake
50 momentarily clamps the bowl 20 to the support 42. When
a brake coil 53 is energized, the mechanical brake surface
54 contacts the wear surface 55 and all bowl vibration is
terminated. A brake coil energization circuit 240 comprises
a comparator 242, a switch 244, a triac 246 and a rectifier
248. When an output 241 from the comparator 242 goes high,
the switch 244 transmits a gating signal to the triac 246
causing 120 volt alternating current to be transmitted
through the triac to the rectifier 248. The rectifier 248
is a full wave rectifier causing pulsating DC signals to
be applied to the brake coil 53.
The output 241 from the comparator 242 varies
in response to the relative size of signals appearing at
two inputs 250, 251 for that comparator 242. A flrst input
250 is coupled to the gain of 47 amplifier 224 and therefore
transmits an oscillating signal proportional to the amplitude
of bowl vibration to the comparator 142. A second input
20' 251 is coupled to the control input 162 from the counter
and is maintained at a value of approximately 10 volts during
forced bowl vibration and drops to a value of about 1 volt
when braking action is initiated. During normal bowl vibration
therefore the input 251 is maintained at a value greater
than the input 250 and the coil remains deenergized. When
the signal 162 from the counter goes low, the input 251
becomes less than the input 250 and the brake coil 53 is
energized. This energization causes the wear surface to
be attracted towards the brake 50 and mechanically clamps
bowl oscillation.
Since the mechanical brake is slower acting than
24
~ 6 ~ ~
the dynamic braking, however, by the time the mechanical
brake contacts the wear surface substantially all bowl vibra-
tion should have been terminated. As bowl vibration dimin-
ishes, the input 250 from the gain of 47 amplifier 224 also
diminishes and after a certain time period the output 241
fr~m the comparator 242 again goes low deenergizing the
brake coil 53. Thus, during normal operation, the brake
50 only contacts the surface 55 for a short period of time
until the coil 53 is deenergized. By completely damping
bowl coil motion the brake 50 provides another safe guard
against the SCR 131 driving the bowl 20 back into oscillation.
That is, when the brake clamps the bowl 20 the amplified
Hall signal at the input 220 must be zero so the comparator
138 generates a high output to deactivate the brake SCR
131.
While a preferred embodiment of the invention
has been disclosed in detail, various modifications or altera-
ons may be made herein without departing from the spirit
and scope of the invention set forth in the appended claims.
