US3800935A

US3800935A - Conveyor drive control system

Info

Publication number: US3800935A
Application number: US00185246A
Authority: US
Inventors: C Montgomery
Original assignee: FAUVER J Inc
Current assignee: FAUVER J Inc
Priority date: 1971-09-30
Filing date: 1971-09-30
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

A control system for a conveyor drive which is particularly adapted to be utilized in conjunction with a flaskless-molding system wherein the two halves of the mold are formed on opposite sides of a single, unitary, sand structure, successively manufactured, identical halves of the mold being brought together on a conveyor system by means of a ram, the control system controlling the amount of pressure introduced to the end of the plurality of aligned molds being controlled by the control system of the present invention. The control system includes a pressure sensing transducer to sense the hydraulic pressure operating a ram in a flaskless mold system, the ram being utilized to push a plurality of flaskless molds unto a conveyor, the control system being utilized to equalize the pressure in the ram by controlling the speed of a conveyor unto which the flaskless molds are being pushed. The control system also includes a zero speed adjust to insure that the conveyor is when the ram is fully retracted and also an adjustment to provide a creep speed so that the conveyor drive is being operated at a low speed to take up the belt slack in the conveyor drive and also to initially stretch the belt prior to full operation of the conveyor drive.

Description

United States Patentv [191 Montgomery Apr. 2, 1974 CONVEYOR DRIVE CONTROL SYSTEM [75] lnventor: Clifford S. Montgomery, Dallas,

Tex.

[73] Assignee: J. N. Fauver, Inc., Madison Heights,

Mich. I

[22] Filed:- Sept. 30, 1971 [21] Appl. No.: 185,246

[52] US. Cl. 198/24, 198/39 [51] Int. Cl. 865g 47/00, 365g 69/00 [58] Field of Search 198/24, 39, 40, 226, 1

[56] References Cited UNITED STATES PATENTS 3,008,563 11/1961 Carter 1. 198/24 3,430,751 3/1969 Bateson 198/39 Primary ExaminerRichard E. Aegerter Attorney, Agent, or Firm-Harness, Dickey & Pierce [57] ABSTRACT A control system for a conveyor drive which is particularly adapted to be utilized in conjunction with a flaskless-molding system wherein the two halves of the mold are formed on opposite sides of a single, unitary, sand structure, successively manufactured, identical halves of the mold being brought together on a conveyor system by means of a ram, the control system controlling the amount of pressure introduced to the end of the plurality of aligned molds being controlled by the control system of the present invention. The control system includes a pressure sensing transducer to sense the hydraulic pressure operating a ram in a flaskless mold system, the ram being utilized to push a plurality of flaskless molds unto a conveyor, the control system being utilized to equalize the pressure in the ram by controlling the speed of a conveyor unto which the flaskless molds are being pushed. The control system also includes a zero speed adjust to insure that the conveyor is when the ram is fully retracted and also an adjustment to provide a creep speed so that the conveyor drive is being operated at a low speed to tak e up the belt sl ack in the convefir dri ve and also to initially stretch the belt prior to full operation of the conveyor drive.

MTENTEUAPR 2l974 3.800.935

sum

1 or 7 INVENTOR.

PATENTED 2 I974 SHEET 8 BF 7 INVEI hOR.

CONVEYOR DRIVE CONTROL SYSTEM BACKGROUND AND SUMMARY OF THE DEVELOPMENT This invention relates generally to a control system for a conveyor drive and more particularly to a control system which is adapted to be utilized in conjunction with a drive motor for a conveyor belt, the conveyor belt being utilized to move a plurality of flaskless molds away from a mold manufacturing assembly.

-The most commonly used type of molding process involves sand casting wherein a casting is formed in a sand mold, the mold being formed ofa mixture of sand grains, clay, water, and additives used to improve such properties as thermal stability, surface finish, and hot strength. In forming a mold of this type, the sand is packed around a suitable pattern, the sand and pattern being surrounded by a container or'flask of suitable size. The sand is generally rammed in place by molding machines to produce the desired degree of packing by a squeezing action, a jolting action; a combination of squeezing and jolting or by a throwing or slinging action. The mold is then split into two halves, the cope and the drag, and the mold is ready for casting. The two halves of the mold are then closed and clamped or weighted to prevent the cope from floating when the casting is poured.

A second type of sand casting, commonly known as shell molding, involves the process of permitting said mixed with a resin binder to come in contact with a pattern heated to an elevated temperature, approximately 350 to 500 F. Excess sand mixture is removed, leaving a thin shell of sand-plastic mixture adhering to the pattern. After heating in an oven to cure the shell, the latter is stripped from the pattern by an ejecting device. The shell halves are then clamped together and may be backed with a support assembly, for examplemetal shot, prior to pouring.

While the above processes are commonly used, the processes have inherent limitations as to the fineness'of surfact finish, the presence of fins on the resulting casting, the presence of flasks and the limitation of speed in developing the molds. In order to alleviate these limitations, a completely automatic flaskless molding machine assembly was developed to permit the manufacture of a continuous fiaskless series of molds along a pouring conveyor to form a rectilinear string of molds. Such a machine is produced and marketed under the tradename DlSAMATlC and produced by DANSK [N- DUSTRI SYNDlKAT A/S of Copenhagen, Denmark.

Basically, the DISAMATIC machine contains a' molding chamber which consists of four fixed walls and two movable walls, the first being characterized a counter pressure plate which carries the front pattern plate and the squeeze plate which forms the rear closing wall for the molding chamber. The counter pressure plate forms one-half of the mold to be mated with the other half of the mold of the preceding mold and the squeeze plate carries the rear pattern for the half of the mold to be mated with a succeeding mold. Thus, such mold formed in the molding chamber contains both halves of the mold which are integrally formed, the front half of the mold being adapted to be mated with a preceding mold and the back half being adapted to be mated with a succeeding mold. The counter pressure plate is adapted to be tilted to the horizontal position after the mold is formed and the squeeze plate is adapted to be mounted or forms the front portion of a hydraulic ram system, the hydraulic ram system being utilized to provide the hydraulic pressure to squeeze the mold and also to provide the force necessary to carry the formed mold out of the DISAMATIC machine. The DlSAMATlC machine also includes a sand hopper from which sand is fed into the molding chamber positioned therebelow under controlled pressure conditions.

In operation, the molding chamber is connected to the sand hopper through an injection slot in the top of the mold chamber. The filling process is controlled by a level indicator incorporated in the sand hopper and sand is fed into the molding chamber by means of compressed air which forces the sand through the injection slot. After filling, the front tiltable pattern plate, referred to above as the counter pressure plate, is kept in a fixed position and the rear squeeze plate is moved forward under the force of the hydraulic piston to compress the sand within the molding chamber. The squeeze plate stops this movement when the pressure on the mold face has reached the desired value, which value may be adjusted. During the squeeze operation a vibratory motion may be introduced to the pattern to insure uniform density of the sand. After sufficient pressure is achieved in themold, the front pattern plate is vibrated to strip the mold from the front pattern plate and the front pattern plate is tilted up to a horizontal position so that the molding chamber is open in the front. The rear pattern plate is then actuated by the by draulic-cylinder to push the formed mold out of the molding chamber and into engagement with the previously manufactured mold, certain of the preceding molds being supported on a table extending from within the mold chamber to aposition exterior to the mold chamber. The rear pattern plate is vibrated after it has concluded its movement to the front position to strip the rear pattern plate from the formed mold. The piston is then returned to its starting position and the mold chamber is again closed to repeat the process of manufacturing a succeeding mold.'

From the foregoing, it is seen that a mold is pushed into mating engagement with a previously manufactured mold to form a mold cavity therebetween, the

molds being adapted to exactly mate and eliminate the fin line. As each succeeding mold is manufactured and pushed into engagement with the previously manufactured mold, the entire string is pushed forward on to a conveyor assembly, the conveyor eassembly being operated by suitable rotary power devices. The molds are then conveyed to a pouring station wherein molten metal is poured into the mold cavity.

As may become apparent from the foregoing description, certain pressures are generated along the longitudinal direction of the series of mating molds, which pressures increase as the number of molds increases and, under certain conditions, may be greater than the unsupported molds may be able to withstand. Under these conditions, the molds are crushed by the conveying force of the hydraulic ram. it is this undesirable crushing action of the molds to which the invention is primarily directed.

As stated above, the manufactured molds are slid a short distance across a supporting table by means of a hydraulic ram, the molds then being positioned on a conveyor belt for movement toward a pouring and ultimate shake-out station. In conveying the molds to the pouring station, it is imperative that a certain degree of pressure be created and maintained across the face of the mold halves to insure that a proper mating of the molds is achieved during the molding process. Accordingly, it has been discovered that, by controlling the drive motor for the conveyor belt in accordance with the sensed pressure across the face of the molds, the problem of crushing of the molds and achieving uniform pressure across the mating mold halves, has been solved.

In order to accomplish the above results, the system of the present invention includes a pressure transducer which is adapted to sense the ram pressure, or a function thereof, during the period that the ram has engaged the previously manufactured stack and the time that the ram reaches the end of its stroke. This signal is fed through pre-amplifier, the output of which is fed to a servo amplifier to control the operation thereof. The output of the servo amplifier is used to control an actuator which in turn controls the speed of the conveyor being driven. The system further includes an actuator feedback arrangement which is utilized to sense the operation of the actuator to provide a reference signal for the pressure transducer signal, the two signals being balanced by the servo amplifier in controlling the operation of the actuator. The actuator is a bidirectional device whereby the actuator may be driven in either direction to speed up or slow down the conveyor in accordance with whether the pressure transducer signal is greater or less than the actuator feedback signal.

In the preferred embodiment, the actuator is selected to be a delta actuator manufactured by the Heli-Coil Corporation, the output of the delta actuator being utilized to drive the control arm of a Sundstrand hydrotransmission device. The Sundstrand transmission is a bidirectional, variable-displacement pump, the displacement and direction of which is controlled by an over-center swashplate, as is common in the art. The output of the Sundstrand transmission is utilized to control a staffa motor manufactured by the'Double A division of Brown and Sharpe Manufacturing Comparry. Theoperation of the delta actuator is sensed by an actuator feedback potentiometer which is utilized as a second input signal to the servo amplifier, this signal having the capability of varying in magnitude from the signal generated by the pressure transducer and also being capable of having a positive or negative polarity relative thereto. Thus, the operation of the actuator is controlled both as to direction and magnitude by the difference in potential between the actuator feedback signal and the pressure transducer signal and also the relative polarities of these latter two signals.

The system also includes a circuit for controlling the speed of the conveyor belt when the hydraulic ram is fully retracted, this speed being ideally adjusted to zero. Further, a second circuit is provided to introduce a creep speed to the conveyor belt when the stack of previously manufactured moldsis engaged by the mold just manufactured so that the slack and stretch in the conveyor belt may be taken up prior to acceleration of the main stack by the hydraulic ram.

It is to be understood that the units described above for controlling the speed of the conveyor in accordance with the sensed pressure are described purely for illustrativepurposes as forming a preferred embodiment of the system of the present invention and are not to be considered limiting. It is to be understood that other components could be selected for a hydraulic system and, on the other hand, a purely electrical drive system could be utilized incorporating an eddy current clutch, a magnetic particle clutch or the like. It is to be further understood that the system, while it is described in the environment of a flaskless mold conveyor control system, that other environments could be utilized in practicing the principles of the present invention.

Accordingly, it is one object of the present invention to provide an improved control system for a conveyor drive.

It is another object of the present invention to provide an improved control system for a conveyor drive incorporated in a system which includes means for laterally pushing material unto the conveyor. I

It is a further object of the present invention to provide an improved control system for the drive motor of a conveyor utilized in association with a flaskless molding assembly. I

It is still another object of the present invention to provide an improved control system for controlling the pressure created between articles on a conveyor system, the pressure being created by a hydraulic ram.

It is still a further object of the present invention to provide an improved control system for controlling the pressure created between articles being conveyed from one point to another point, the conveying system including a ram for pushing the articles onto a conveyor belt,

It is still a further object of the present invention to provide an improved electrical control system for controlling the speed of a conveyor belt, the conveyor belt being adapted to control the pressure created at the interface of successive articles by a hydraulic ram.

It is still another object of the present invention to provide an improved control system for a conveyor, the speed of the conveyor being regulated in accordance with the sensed pressure between the articles being conveyed to the conveyor by a hudraulic ram, the pressure between the articles being manifested by the hydraulic ram pressure.

It is still another object of the present invention to provide an improved control system for a conveyor belt utilized in association with a flaskless mold manufacturing assembly which is reliable in operation, relatively inexpensive to produce and alleviates certain problems of prior molding assemblies.

Further objects, features and advantages of this invention will become apparent from a consideration of the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic elevation view of a flaskless mold manufacturing machine, identified above, and

further illustrates the conveyor system incorporating FIG. 7 is a schematic diagram of a portion of the hydraulic system of the present invention.

Referring now to FIG. 1, there is illustrated a DISA- MATIC machine 10 which is adapted to produce the flaskless molds 12 described above, the ram of the DISAMATIC machine 10 being adapted to push successively produced molds onto a pouring table 14 as each mold is produced. The molds are caused to come into engagement, one with the other, as each successive mold is pushed onto the table 14 and the molds are conveyed to a pouring station which is directly beneath a pouring ladle 16 containing the molten metal. The molds, with the molten metal contained therein, are then pushed down to a conveyor assembly 18 by means of the ram in the machine 10, the conveyor assembly being adapted to move the filled molds from the table '14 to a shake-out station 20.

As is readily apparent, thepressure at the interface between two molds once the molten metal has been introduced to the cavity must be maintained sufficiently high to insure that no leakage of the molten metal occurs at the interface. If leakage occurs, then a fin will be produced at the parting line of the mold. Also, this pressure must not be permitted to be of such a magnitude that the molds are crushed by the pushing action of the ram. It will be remembered that the molds 12 are flaskless and do not have any confining members to insure that the molds remain intact. To this end, the conveyor system 18 includes a controlled drive, to be described briefly in conjunction with FIG. 3, for maintaining the pressure at the interface at a preselected level. This pressure is sensed by sensing the ram pressure used to push the molds 12 at the right end of the series of molds.

The conveyor system includes a belt 24 onto which the molds are pushed by the ram, and the belt is driven by a suitable motor, in this case a Sundstrand transmission and Staffa motor combination. As will be apparent from a further description of the system of the present invention, the pressure level at the hydraulic ram is sensed by a transducer which provides a reference signal for the servo controller system. The output of the servo controller system controls a delta actuator, the actuator providing a feedback signal for the servo controller, a comparison between the feedback signal the transducer signal assuring that the delta actuator is operating in accordance with the sensed pressure. The output of the delta actuator is fed to the Sundstrand transmission which controls the operation of the Staffa motor. The Staffa motor is utilized to control the speed of the conveyor belt 24, the speed of the conveyor belt 24 causing an increase or decrease in the necessary pressure required to push the manufactured molds down the line.

Referring now to the FIG. 2, there is illustrated the various steps in producing a flaskless mold, the steps being broken down into six phases of the molding cycle. Basically the DISAMATIC machine includes a molding chamber 30 which is closed by four fixed walls and two movable walls. The two movable walls include a counter pressure plate 32 which carries the front pattern plate 34 and the squeeze plate 36 which forms the rear closing wall for the mold and also carries the rear mold plate 38.

Sand is introduced into the mold chamber 30 by means of a sand hopper 40, the feeding of the sand being controlled from an air receiver chamber 42. The operation of the squeeze plate is controlled by a ram member 46, the position of which is controlled by the pressure within a pressure chamber 48. The operation of the counter pressure plate is controlled by means of a pair of tie-rods 50, 52 the position of the tie-rods being controlled by a second ram member 56 connected thereto. The pressure within the chamber 48 is controlled by a third ram member 60 which controls the volume of a chamber 62, the chamber 62 being in fluid communication with the pressure chamber 48. Also, there is a second pressure inlet to the pressure chamber 48 formed by an inlet member 66.

During the first phase of the molding cycle illustrated in 2a, the molding chamber 30 is connected to the sand hopper 40, the sand hopper being fed by a conveyor, vibrator or similar device through an injection slot in the top of the sand hopper. The filling process is controlled by a level indicator incorporated in the sand hopper, the level indicator providing a filling output pulse when the said level in the hopper has reached a lower limit. Sand is fed into the molding chamber from the hopper by means of compressed air supplied from the air receiver 42, the sand being forced through an injection aperture. After the molding chamber has been filled and excess air has been exhausted, the sand gate to the sand hopper opens to refill the sand hopper with molding sand. During the filling process, the counter pressure plate 32, with its associated front pattern plate 34, is in the position shown in FIG. 2a. Similarly, the ram 46 is fully retracted to extend the volume of the molding chamber to its capacity. Also, the ram 56 controlling the tie-rods 50, 52 is in the position shown.

The next phase of the molding cycle is characterized as the squeezeoperationwherein the front tiltable pattern plate, characterized the counter pressure plate 32, is kept in a fixed position, thereby keeping the molding chamber closed at the front thereof. The squeeze plate 36, including the rear pattern plate, is pushed into the molding chamber by the piston 46. This movement is controlled by means of pressurized fluid introduced into the chamber 48 from the input inlet 66. This causes the ram 46 to move to the left, or forward, thereby compressing the sand contained within the mold chamber 30. The squeeze plate stops its movement when the pressure on the mold face has reached the desired value. The mold face pressure can be adjusted to give any desired degree of hardness. During the squeeze operation, the pattern plates are vibrated by the vibrators built into the pattern plate bases.

FIG. 2c illustrates the stripping phase of the molding cycle wherein the front pattern plate is stripped from the mold by vibrating the front pattern plate. In this first stripping portion of the cycle, the ram 46 is held turn causes tie-rods 50, 52 to also move forward in conjunction with the ram 56. This forward motion causes the counter pressure plate 32 to move away from the face of the mold and also linkages are provided to tilt the counter pressure plate 32 to the horizontal position illustrated in FIG. 2c. in order to provide a positive movement of the ram 56, suitable pressurized fluid is introduced to a second pressure inlet 70 to create a pressure on the back face of a plate 72 formed on the face of the ram 56. The system includes means for holding the mold surfaces absolutely true by a high precision guide system and, while the mold chamber is open in the front, cores maybe inserted at the front of the mold during this phase of the molding cycle.

The fourth phase of the molding cycle, characterized the closing of the molds portion, is illustrated in FIG. 2d wherein the just manufactured mold is moved forward into contact with a previously manufactured mold by means of forward movement of the ram 46. The ram 46 is moved by means of pressure introduced into the pressure chamber 48 by movement of the ram 60. This movement is created by means of a further pressure inlet 76 to create a pressure at the back face of the face plate of the ram 60. During this operation the ram 56 is held at the previous position to insure that the counter pressure plate 32 is in its horizontal position. It is during the closing phase of the molding cycle that the control system of the present invention becomes critical. During the closing operation, the rear pattern plate 36 conveys the mold out of the chamber, slowly at first and thereafter more rapidly. Immediately before the mold reached the previously manufactured mold, the speed is reduced and the mold very slowly closes with the preceding mold. Thereafter, the movement accelerates, in association with the control of the control system of the present invention, and the entire string of molds is pushed forward at increasing speed over a distance equal to the thickness ofa mold. It is this acceleration of the molds which causes the acceleration of the conveyor belt to limit the pressure created between the interfaces of two successive molds.

Referring now to FIG. 2e, there is illustrated the second stripping operation wherein the rear pattern plate is vibrated to strip the pattern plate from the mold and retract the hydraulic ram 46. During this portion of the operation, the pressure chamber 48 is evacuated of fluid an positive pressure is introduced into a pressure inlet 80 and this causes a positive pressure on the back face of the ram 46 to retract the ram. This retraction creates a pressure in the pressure'chamber 62 to retract the ram 60. During this phase of the operation, the rear pattern plate 36 is vibrated after it has concluded its movement to the front position and then is returned at high speed to its starting position in the molding chamber. This starting position of the rearpattern plate is adjustable so that the mold thickness can be varied. When the mold has been delivered and the string of molds fed forward, the second core insertion position is reached and the insertion of cores may be commenced prior to the closing of the mold chamber for the subsequent mold has begun,

FIG. 2f illustrated the final or sixth phase of the molding operation wherein the molding chamber is closed and the starting position described in conjunction with FIG. 2a is obtained. During this portion of the Operation, the ram 56 is retracted to move the tie-rods 50, 52 to their rear-most position. This causes the counter pressure plate 32 to to be moved to its vertical position for the mold closing phase. Also, positive pressure is introduced to the fluid inlet 76 to create a positive pressure on the front face of the ram 60 to return the ram 60 to its original position. The returning of the ram 60 to its original position creates a positive pressure in the pressure chamber 48 to move the piston 56 rearwardly and-thus move tie-rods 50, 52 rearwardly. The system is now prepared for the next molding operation.

Referring now to FIG. 3, there is illustrated a schematic diagram of the drive system for the conveyor belt 24 to control the forward motion and speed thereof. Particularly, the ram 46 is moved forward to push the just manufactured mold into engagement with the previously manufactured mold and to move the entire series of molds forward. This pressure is sensed by means of a pressure transducer, schematically illustrated as the linear potentiometer 82 positioned on the ram. The potentiometer 82 provides a signal to a conveyor drive control system 84, the adjustment of the potentiometer being a function of the adjustment of the variable position arm 86 with respect to a resistance element 88. The pressure created in the ram causes a change in resistance of the element 88 to provide a control signal to the conveyor drive control system illustrated as block 84. The conveyor drive control 84 includes certain adjustment which are representatively illustrated as a lead/lag control adjustment element 90, a loop gain adjustment element 92 and a conveyor speed adjustment 94. These adjustments will be more fully explained hereinafter.

The output of the conveyor drive control is fed to a delta actuator 96, the output of which controls the operation of the hydrostatic transmission and drive assembly 98. The hydrostatic transmission and drive assembly creates a rotary forward motion for the conveyor belt 24 by means of a shaft 106.

Referring now to FIG. 4, there is illustrated the power supply and manual control system which includes the main contactors from the power supply at input terminals 122,124, 126 to a motor 128 for driving the ram. The circuit 120 also includes the various push buttons and relays for'controlling the manual and automatic operation of the system.

Specifically, the input three-phase electrical energy is fed through a plurality of safety switches 130, a switch for each phase the three-phase switches being ganged together, and a plurality of fuses 132 for overload protection. The circuit to the motor 128 alsoincludes a plurality of relay-controlled contactors 134 and a motor safety switch 136. Thus, when the system is to be operated, the switches and 136 are manually closed by the operator. The closure of switches 130 supplies electrical energy to the control system 140 by means of a transformer 1 42 and a pair of conductors 144, 146. However, in order for electrical energy to be fed to the motor 128, the switches 136 must also be closed. The secondary of the transformer 142 is connected to a pair of power lines 148, for supplying energy to the control circuit 140. i

The control circuit 140 includes an off switch 154 and an on switch 156, the off switch 154 normally being closed and the on" switch 156 being biased open. After the operator has closed the

switches

132, 136, the on" switch 156 is closed and energy flows from the transformer 142, through the conductor 148,

through a relay coil 158, to the conductor 150. The energization of relay 158 causes holding contacts 160 to close thereby maintaining the energization of the relay 158 even though the switch 156 is again opened. The closure of switch 156 also energizes an indicator light 162 to indicate that the holding circuit is operable.

The energization of relay coil 158 also closes a pair of contacts 166 associated therewith to energize a stop/start circuit which includes a normally closed stop button 168 and a normally open start button 170. The operator then closes the start button 170 to provide energy through the contacts 166, the stop button 168, the start button 170 to a relay coil 174. The relay coil 174 is connected to the other side of the line at conductor 150 through a pair of normally closed overload contactors 176, 178, the overload contactors being used to sense certain overload conditions within the system, as is common in the art. If the overload condition is sensed, one of the contacts 176, 178 will open to disable the stop/start circuit. Also, the energization of relay 174 illuminates an indicator light 180.

The energization of the relay 174 closes a normally open holding contact 186 which is connected in parallel with the start button 170 and in series with a pair of normally open contacts 188. The contacts 188 are controlled by the energization of a relay 190 connected across one of the phases supplying the motor 128. Thus, if the motor switches 136 are closed and energy is fed to the motor 128, the relay coil 190 will be energized. The energization of the coil 190 closes contacts 188 to energize the relay 174.

The energization of the relay 158 also closes a pair of normally open contacts 194 to supply energy to a manual/automatic circuit which provides a capability for the operator to select either the manual mode of operator for the control system or the automatic operation for the control system. .The relay 158 also closes a pair of normally open contacts 196 which supplies an output signal to a pair of output terminals 198, 200 to provide an indication that the system is on or for some other purpose. Also a solenoid 202 is energized for any suitable purpose.

Referring back to the manual/automatic circuit, the system includes a manual/automatic switch 206 which includes three positions, the off position illustrated, the manual position when the switch is uppermost and the automatic position when the switch is in the lower position. With the system in the center or off position, the circuit connected between contact 194 and conductor 150 is de-energized. When the switch 206 is moved to the manual position, the armature 208 is moved upwardly to bridge the contacts 210, 212, and also contacts 214, 216 are bridged by armature blade 218. The bridging of contacts 210, 212 supplies energy to the coil of a relay coil 220 to provide a signal to conveyor drive control circuit 222 that the operator has selected the manual portion of the operation. Also, a manual indicating light 224 is illuminated.

The bridging of contacts 214, 216 by blade 218 also supplies, a signal to the conveyor drive that either the manual or automatic mode of operation has been selected and the selector switch is not in the off position. Thus, the energization of relay 220 and the movement of armature 218 supplies information to the conveyor drive control circuit 212.

On the other hand, if the automatic mode of operation is selected, the blade 208 is moved down to bridge energize relay 220 but does illuminate automatic indicator light 238. Also, the bridging of

contacts

234, 236 provides an indication to the conveyor drive control circuit 222 that either the automatic or manual operation has been selected. The non-energization of relay 220 indicates that the automatic operation has been selected.

Referring now to FIGS. 5 and 6, there is illustrated a schematic diagram of the control system 250 of the present invention which basically includes a pressure sensing transducer circuit 252 selected to be a strain gauge bridge to sense the pressure in the ram. The output of this system is fed to a differential amplifier circuit 254, the output of which is fed, in turn, to a servo amplifier circuit 256. The servo amplifier circuit 256 is utilized to control the operation of a delta actuator circuit 258, symbolically illustrated by illustrating the actuator coil. The circuit further includes a feedback loop which takes the form of an actuator feedback potentiometer circuit 260 which senses the operation of the hydraulic system including the delta actuator.

The signal is fed through a differential amplifier circuit 262 which also includes an input from a manual adjust, zero speed adjust and creep speed adjust circuit 264. The output of the differential amplifier circuit 262 is fed to the upper input of the servo amplifier circuit 256 to control the delta actuator circuit 258 in accordance with the signal generated by the pressure transducer circuit 252 and the actuator feedback circuit 260 during the period that the I ram is pushing the mold stack.

Referring particularly to the details of the pressure transducer circuit, the circuit includes a strain gauge bridge including four

resistive elements

270, 272, 274, 276. The bridge is fed a positive and negative direct current potential at

input terminals

278, 280 respectively, the direct current potential being applied across the A and B nodes of the strain gauge bridge. The output of the bridge is derived across nodes C and D and fed to the input circuit of the differential amplifier 254 by means of

resistors

282, 284. The differential amplifier circuit 254 includes an operational amplifier 296 connected as a differential amplifier, the output of which is applied to a node 290. The operational amplifier 286 is connected in the common differental amplifier configuration.

During the manual operation of the circuit, a manual- /automatic switch 294 is in the position shown with an armature 296 in engagement with a contact 298. This switch is controlled by the relay 220 described in conjunction with FIG. 4. Also, prior to the engagement of the stack by the ram, and prior to the closing of a limit switch set up to sense the engagement of the stack with the ram, a second switch 300 is in the position shown, with an armature 302 in engagement with a contact 304. This is shown as the normal position. When the limit switch is engaged, the armature 302 is moved upward to the second contact 306. However, before this movement, the output of the operational amplifier 286 is grounded through a circuit including node 290, a resistor 310, switch 300, conductor 312, switch 294 to ground at node 314. When the switch 300 transfers to the upper or operate position, the input to the servo amplifier circuit 256, which would normally be from 1 1 the differential amplifier 286 is grounded through the automatic/manual switch 294.

Assuming that the operator has placed the system in the automatic mode of operation, the switch 294 would be in the opposite position with the armature 296 in contact with the upper terminal 318. This connects the node 290 to the input circuit of the servo amplifier 256 through resistor 310, a conductor 320, the switch 294 and a conductor 322. However, before engagement of the stack by the ram, the switch 300 is in the position shown to ground the node 290 through the switch 300, the conductor 312 and a conductor 324. After the engagement of the stack, the differential amplifier output is fed to the lower input of the servo amplifier circuit 256. The resistor 310 has been provided to limit the current when the output of the differential amplifier is shortened to ground, prior to the time that the switch 300 is moved to the operate position.

Referring now to the feedback circuit, the circuit 260 includes a potentiometer 326 which is fed a positive voltage at the upper end thereof from an input terminal 328 and a resistor 3 30 and anegative voltage at the lower end thereof from an input terminal 332 and a resistor 334. The output of the actuator pot'is fed to the upper input circuit of a differential amplifier circuit Thus, when the system is in automatic, the signal level on conductor 374 will be fed to the lower input circuit of the operational amplifier 336 through the switch 344. Prior to the engagement of the stack by the ram, the armature 376 is in the lower most position to provide zero speed for the conveyor; After the engagement of the stack by the ram, the conveyor is permitted to creep to take up belt slack and stretch. Also, after 1 the engagement of the stack by the ram, the upper 262 and particularly to operational amplifier 336 by means of a slider arm forming a part of the potentiometer 326. This slider arm is connected by means of a conductor 338 and a resistance 340.

Referring now to the circuit 264 and assuming that the system is in the manual mode of operation, an automatic/manual switch 344 will be in the position shown whereby the armature 346 is in contact with the lower element 348. This connects the lower input of the differential amplifier 236 through a conductor 350 and a resistor 352. The lower contact 348 is connected to the slide 356 of a potentiometer, including

resistors

358, 360,.362, the

resistors

358, 360, 362 beitn connected across a positive and negative 15 volt source of potential at input terminals 364, 366. This potentiometer is only in the circuit whenthe system is switched to manual. The slider 356 is adjusted so that the belt does not move then the system is switched to manual and a forward/reverse switch is set to off.

. On the other hand, if the system is in automatic, the armature 346 is in the upper position in contact with an element 370, which contact is connected to an operate normal switch 372 through a conductor 374. When the system is in the normal mode, that is prior to the ram engaging the stack and closing the above-described limit switch, an armature 376 of the switch 372 is in the position shown to thereby connect the conductor 374 to a potentiometer 380. The potentiometer 380 is adjusted, by means of a slider 382, to insure that the speed of the conveyor is zero when the ram is retracted and prior to the engagement of the ram with the stack, this potentiometer is also connected across the 15 volt source of potential at terminals 364, 366. When the limit switch is engaged and closed, the armature 376 moves to the upper position to connect a third potentiometer 386 to the conductor 374, the potentiometer 386 being utilized to adjust the creep speed of the conveyor after the ram has engaged the stack. This is necessary to permit the system to take up belt slack and to stretch the belt prior to full acceleration of the system.

input of the operational'amplifier 336 is switched to ground by means of another normal/operate switch 390, the armature 392 being transferred to the upper contact 394 when the stack is engaged.'Thus, the operational amplifier 336 senses the signal from resistor 340 connected at one end to ground through the switch 390 and also senses the signal from the potentiometer 386 after the ram has engaged the stack. The potentiometer 386 is only in circuit during the push portion of the cycle and sets the threshold pressure at which the conveyor runs in the forward direction.

The output of the differential amplifier 336 is fed to the upper input of the servo amplifier 356, particularly an operational amplifier 398 through a resistor 400. During the push mode of operation, where the stack is being pushed by the ram, the operational amplifier 398 provides an output signal at node 402 to control the energization of the delta actuator 258 either in the forward or reverse direction to control-the acceleration or deceleration of the conveyor. The servo amplifier 256 also includes a position gain feedback circuit, including an adjustable resistor 406, to adjust the conveyor velocity ram pressure operation. Also, an indicator lamp 410 has been provided to provide a visual indication of the null operation of the circuit wherein the lamp is not illuminated when the system has reached a null.

The system also includes a latching relay circuit 416, a manual/operate/normal relay circuit 418 and a power supply circuit 420. Referring particularly to the power supplies, there is provided a 12 volt-supply at 422, a +15 volt supply at 424, a -15 volt supply at 426 and a +and --l0 volt supply at 428. The power supplies are all connected to the ground at node'314 to provide a common servo system ground. Also, volt alternating current input energy is supplied to the power supplies through a power-on relay and switch arrangement including a relay 432 and a pair of gang switches 434, 436. The 120 volt supply is also connected to the upper end of each of a manual relay coil 438, an operate relay coil 440, and a normal relay coil 442 through a conductor 444. The lower ends of the

coils

438, 440, 442 are connected to a selector switch and two limit switches respectively.

The relief relay latching circuit 416 includes a relay coil 450 which is energized in response to the ram engaging the stack and thus transferring the armature of a normal operate switch from a normal terminal 454 to an operate terminal 456. When this occurs, a positive 12 volts is fed from an output conductor 458 to relay coil 450 by means of a conductor 460. The relay coil 450 then latches certain circuits within the system during the time that the system is sensing pressure or after the stack has been engaged by the ram.

Referring now to FIG. .7 there is illustrated certain details of the hydraulic system associated with the control of the present invention and particularly include a Sundstrand pump assembly 470 which is controlled by the delta actuator, a Staffa motor 472, the operation of which is controlled by the Sundstrand pump assembly 470, a relief valve assembly 474 which controls the maximum pressure at which the Staffa motor may operate, and a cooling system 476 which is utilized to control the cooling of the oil flowing through the Sundstrand pump assembly.

Referring particularly to the Sundstrand pump assembly, the pump includes a control element 480 for controlling the pressure and direction of flow of fluid to the Staffa motor, this element 480 being controlled by means of a mechanical linkage 482 to the delta actuator and also by means of a fluid regulator system including an element 484. This element 484 is supplied fluid energy to control the pump through a conduit 486, the fluid being filtered by a filter element 488. Suitable pressure gauges 490, 492 are provided to sense the pressure within the Sundstrand pump assembly. Also, check valves 496, 498 and an overpressure valve 500 is provided. The pump is driven by a 20 horse-power, 1,800 rpm motor 502, this being the motor described at 128 in conjunction with the. description of FIG. 1. The oil for the Sundstrand pump assembly is supplied from an oil tank 506 through a suitable filter 508. The return to the tank 506 is provided by conduit 510 through a suitable heat exchange unit 512. The heat exchange unit is supplied with a suitable coolent, for example water, from an inlet 514 through a temperature responsive valve 516, the return beingprovided by conduit 518.

The Staffa motor 472 is utilized to drive the conveyor belt 24 described in conjunction with FIGS. 1 and 3 and the hydraulic pressure of the Staffa motor is controlled by the relief valve assembly contained within block 474.

With the hydraulic system of the present invention, ram pressure is available to the transducer only during the time when the molds are being pushed out on the pouring rails or cable. This is accomplished by energizing a solenoid valve when the limit switch is engaged signalling that the ram has engaged the stack. The making of this limit switch produces the ram pressures at the transducer. This pressure, when the ram is pushing only one block, will be of the order of 5 to 8 psi. When the ram pushes this block into engagment with the previousl manufactured molds, this pressure signal rises to approximately 35 psi or higher due to the fact that the static friction is greater than the sliding friction of the stack. The ram pressure then will settle to approximately 35 psi during the time that the ram is pushing the stack after the static friction has been broken.

When the ram reaches approximately full stroke, a second limit switch is engaged to de-energize the above solenoid valve and dump pressure from the transducer to the supply tank. The solenoid remains deenergized during the squeeze portion of the mold manufacturing process to insure that the extremely high pressures of the mold manufacturing process are not transmitted to the transducer.

In operation, the electronic control system generates a signal to the delta actuator, the delta actuator moving the control lever on the Sundstrand pump through the mechanical linkage 482. This mechanical linkage positions the swash plate within the pump as is common in the art. The position of this swash plate determines the amount of oil the pump will pump to the hydraulic Staffa motor 472, thus controlling the speed of this motor and the speed of the conveyor. In this way, the

circuit of the present invention controls the acceleration and deceleration of the drive and also controls the maximum speed of the drive.

While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. In a conveyor system including conveyor assembly having a conveyor belt and a motor drive for the belt, a source of workpieces, and a ram assembly for pushing the workpieces from a position adjacent the source to a position on the conveyor belt, the improvement comprising a control system for controlling the speed of operation of the conveyor assembly in accordance with the sensed force exerted on the workpieces by the ram at least during certain times of movement of the workpieces intermediate the start and end of the ram movement, force sensing means associated with the ram for sensing the force of the ram exerted on the workpieces intermediate the start and end of movement, maximum force setting means for establishing a desired force to be exerted by the ram, comparison means connected to said force sensing means and said force setting means for comparing said sensed force with said set force and generating a control signal, output control means connected to said comparison means and the conveyor motor drive for controlling the speed of the drive in accordance with the control signal and, thus, the sensed force and the set force to maintain the force at said desired force, said force sensing means including transducer means connected to sense the pressure of said ram, and a servo interconnected with said output control means and including an input signal from said transducer means.

2. The improvement of claim 1 further including a switching means connected to sense the position of said ram, said switching means disabling the input signal from said transducer means to said servo amplifier prior to the time said ram fully engages said workpieces.

3. The improvement of claim 1 wherein said servo amplifier includes a second input circuit, said comparison means being connected to said input circuit for supplying said control signal.

4. The improvement of claim 3 wherein said comparison means includes first and second input circuits, one of said input circuits being adapted to be supplied at least one ofa plurality of input signals, one of said input signals being set to control said control signal such that a creep speed is established in said motor drive prior to substantial acceleration of the ram.

5. The improvememt of claim 4 further including zero speed signal generating circuit connected to said one input circuit, said zero speed input circuit establishing zero speed for said control drive when said ram is out of engagement with said workpieces.

6. The improvement of claim 5 wherein said zero speed input circuit includes a manual and automatic zero speed adjustment potentiometer, said manual and automatic potentiometers being in circuit with said first input circuit during manual and automatic operations, respectively.

7. The improvement of claim 4 wherein said system further includes a feedback circuit interconnected to sense the operation of said conveyor motor drive, the output of said feedback circuit being fed to the second input circuit of said comparison means, said feedback circuit being bidirectional in polarity to alter the operation of said comparison means in accordance with the operation of said motor drive.

8. The improvement of claim 7 wherein said motor drive includes 'a delta actuator, said feedback circuit including a potentiometer interconnected to sense the operation of said delta actuator. I

9. The conveyor system of claim 8 further including a Sunstrand transmission driven by the delta actuator, and a Staffa motor controlled by the Sunstrand transmission, the improvement further including said output control means being connected to the delta actuator for driving the delta actuator bidirectionally.

10. The improvement of claim 9 wherein said servo amplifier further includes a position gain circuit for establishing a linear dimension of travel per unit of ram pressure of the ram.

11. The improvement of claim 10 wherein said servo amplifier is an operational amplifier, and said position gain circuit is a feedback circuit between the output of said servo amplifier and one of the inputs of said servo amplifier.

12. The improvement of claim 11 wherein said comparison means includes an operational amplifier connected as a differential amplifier.

13. In a conveyor system including a conveyor assembly having a conveyor belt and a motor drive for the belt, a source of workpieces, and a ram assembly for pushing'the workpieces from a position adjacent the 16 a source to a position on the conveyor belt, the improvemerit comprising a method of controlling the speed of operation of the conveyor assembly in accordance with the sensed force exerted on the workpieces by the ram including the steps of sensing the force of the ram exerted on the workpieces at least during certain times of movement of the workpieces intermediate the start and end of the ram movement, establishing a desired force to be exerted by the ram, comparing said sensed force with said set force and generating a control signal, and controlling the speed of the drive in accordance with the control signal and, thus, the sensed force and the set force to maintain the force at said desired force, the ram assembly including a fluid actuated ram and the sensing step including sensing the pressure of the ram.

14. The improvement of claim 13 further including disabling the input signal prior to'the time said ram fully engages said workpieces.

15. The improvement of claim 14 further including establishing a creep speed in said motor drive prior to full acceleration of the ram, and establishing zero spped for said control drive when said ram is out of engagement with said workpieces.

16. The improvement of claim 15 wherein said method further includes sensing the operation of said conveyor motor drive and bidirectionally altering the operation of said control in accordance with the operation of said motor drive, said establishing a linear dimension of travel per unit of ram pressure of the ram.

UNITED STATES PATENT OFFICE CERTIFICATE (ll CRRECTION Patent No. 3,800; 935 Dated April 2 1974 InventOr( Qhfinj S ,ug jgomerv It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 30, "said" should be --sand--. Column 2, line 50, "eassembly" (second occurrence) should be --assembly--. Column 6, line 29, "said" should be --sand--. Column 6, line 683 delete second occurrence "is" and replace with in. Column 7, line 47, "an" should be --and--. Column 9, line 36 "operator" should be operation-m Column 9, line 49 "contact" should be --contactor--. Column 11, line33, "slide" should be "slider- Column 11, line 44, "then" should be --when--. Column 13, line 45, "previousl" should be "previously". Column 16, line 23, "spped" should be -speed -7. ,1: Column 16, line 30, "said", second occurrence, should read and Signed tend sealed this 15th day of October 1974.

' (SEAL) At te s t v MCCOY 1 GZBSON JR. c. MARSHALL DANN Attes ting (if f icer Commiss ioner of Patents M050 (1069 uscoMM-oc scan-pus 9 U.. GOVIRHIFT Plufl OFFICE I I... 0-366-334

Claims

1. In a conveyor system including conveyor assembly having a conveyor belt and a motor drive for the belt, a source of workpieces, and a ram assembly for pushing the workpieces from a position adjacent the source to a position on the conveyor belt, the improvement comprising a control system for controlling the speed of operation of the conveyor assembly in accordance with the sensed force exerted on the workpieces by the ram at least during ceRtain times of movement of the workpieces intermediate the start and end of the ram movement, force sensing means associated with the ram for sensing the force of the ram exerted on the workpieces intermediate the start and end of movement, maximum force setting means for establishing a desired force to be exerted by the ram, comparison means connected to said force sensing means and said force wetting means for comparing said sensed force with said set force and generating a control signal, output control means connected to said comparison means and the conveyor motor drive for controlling the speed of the drive in accordance with the control signal and, thus, the sensed force and the set force to maintain the force at said desired force, said force sensing means including transducer means connected to sense the pressure of said ram, and a servo interconnected with said output control means and including an input signal from said transducer means.

4. The improvement of claim 3 wherein said comparison means includes first and second input circuits, one of said input circuits being adapted to be supplied at least one of a plurality of input signals, one of said input signals being set to control said control signal such that a creep speed is established in said motor drive prior to substantial acceleration of the ram.

8. The improvement of claim 7 wherein said motor drive includes a delta actuator, said feedback circuit including a potentiometer interconnected to sense the operation of said delta actuator.

13. In a conveyor system including a conveyor assembly having a conveyor belt and a motor drive for the belt, a source of workpieces, and a ram assembly for pushing the workpieces from a position adjacent the source to a posItion on the conveyor belt, the improvement comprising a method of controlling the speed of operation of the conveyor assembly in accordance with the sensed force exerted on the workpieces by the ram including the steps of sensing the force of the ram exerted on the workpieces at least during certain times of movement of the workpieces intermediate the start and end of the ram movement, establishing a desired force to be exerted by the ram, comparing said sensed force with said set force and generating a control signal, and controlling the speed of the drive in accordance with the control signal and, thus, the sensed force and the set force to maintain the force at said desired force, the ram assembly including a fluid actuated ram and the sensing step including sensing the pressure of the ram.

14. The improvement of claim 13 further including disabling the input signal prior to the time said ram fully engages said workpieces.