GB2154764A

GB2154764A - Controlled clutch/brake unit

Info

Publication number: GB2154764A
Application number: GB08508827A
Authority: GB
Inventors: Gordon Maurice Sommer
Original assignee: Sommer Co; G M SOMMER CO Inc
Current assignee: Sommer Co; G M SOMMER CO Inc
Priority date: 1982-04-22
Filing date: 1985-04-04
Publication date: 1985-09-11
Also published as: DE3348133C2; JPS58192735A; FR2525538A1; GB2119542B; FR2525538B1; GB2119542A; DE3314105C2; GB2154764B; CA1209498A; GB8307824D0; DE3314105A1; GB8508827D0

Abstract

A clutch/brake unit e.g. for a rotary index table 12 is controlled by means 132, 140, 144 which sense the position of the table or other driven element, means 156 to compare this position with a target position (stored at 152) at which it is desired to halt the table, and means to adjust the position (stored at 158) at which the brake is operated to reduce the error signal resulting from this compression. The brake-operating position is automatically corrected to compensate for drifts in temperature or other factors. Initial values of target position and braking position are entered manually during a teaching cycle. <IMAGE>

Description

1 GB 2 154 764A 1

SPECIFICATION

Index table including controlled clutch/brake unit The present invention relates to an index table including a computer- controlled clutch/brake unit. In one particular application, the present invention relates to a microcomputer con- trolled index table that can be used with any number of stations in either a rotary or linearly indexed application.

Prior art applications of controlled indexing have used complicated servocontrols and di- rect current drive mechanisms which null into a selected target point. In index table applications, strictly mechanical controls have also been used, such as a Geneva movement with a position locating cam or the like. Such applications are slow and cumbersome, need complicated controls for acceleration and deceleration, and do not have significant accuracy. Alternatively, crude indexing may be accomplished by a mechanical stop.

The present invention uses a computer in association with a clutch/brake unit to learn what position exists in a particular application, to learn what movement has to be made to attain a target point, to make corrections itself until the desired target point has been accurately attained, and to keep correcting as the work operation progresses in order automatically to compensate for any error in the system as it drifts off because of temperature or any other factor. The present invention may be used in any of a number of applications where a clutch/brake unit is used, such as oil well pumps where the operator will speed up the pump to a certain point, see what the pressure is, make a calculation as to when the brake should be actuated, and use the learning process to optimize the point and time of pump dwell and the acceleration and deceleration of the pump to obtain a desired pump rate.

In an index table application, the control concept and mechanics of the present invention is elegantly simple and represents a quantum gain in technology, reliability and flexibil- ity over prior art index tables. Target buttons are disposed at selected positions throughout the index table to indicate the index angle at which a workpiece is stopped and at which at least one operation is performed on a work- piece. Any number of stations may be used. The number of stations may be readily altered by detaching and reinstalling the target buttons in newly selected holes without any change to the microprocessor control pro- gram. Thus, the present invention has as one object to provide a reliable, flexible, yet simple control and drive system for a rotary index table. The present invention also has the object of providing the above index table with a pneumatically controlled, oil cooled clutch/- 130 brake unit integrally disposed within the control system of the index table. Yet another object is to provide an extremely accurate and programmable control system for braking the workpiece in the proper position. The index table and its control system, with its high degree of accuracy, in turn can accurately control robots and other ancillary hardware associated with the operation to be performed on the workpiece and environment in which the operation is to be performed.

The present invention is divided from our copending application No. 8307824 (Serial No.2119542) having a similar disclosure in

Claims

which we claim an index table for at least one workpiece, comprising: a

table for supporting a workpiece, including a transmission element for driving said table; drive means including a motor; a housing disposed adjacent said table; a clutch within said housing for actuating movement of said table by operably associating said drive means with said transmission element of said table to drive said table in only one direction; a brake within said hous- ing for stopping movement of the table via the transmission element; means for operably associating the clutch and brake with the transmission element of said table; and control means, comprising means disposed on said table for signalling the position of the workpiece on said table relative to a preselected targetted stopping position of said table, computer means associated with said signalling means for determining the position of said table properly to position a workpiece on said table relative to said preselected targetted stopping position of said table, and comparator means for actuating said clutch or brake in response to the position of said table determined by said computer means, wherein the timing of actuation of said brake by said actuating means when the workpiece is ahead of the desired position of the workpiece determines the accurate placement of the work- piece in the desired position.

According to one aspect of the invention there is provided a controlled clutch/brake unit for use in a work operation comprising drive means; a driven element; clutch means for operably associating said drive means with said driven element when said clutch means is engaged; brake means; and means for controlling said clutch and brake means to control the position of said driven element, including means for setting a zero point, means for actuating said brake to stop said driven element, means for learning in what position the driven element is stopped relative to said zero point, means for learning what movement of said driven element has to be made to attain a selected target stopping point set relative to said zero point, means for self-correcting any error between an actual stopping position of said driven element and said target stopping point until the desired target stopping point 2 GB 2 154 764A 2 has been attained within a selected range of accuracy, and means for continued correction of any error between an actual stopping position of said driven element and said targeted stopping position as the work operation progresses in order to automatically compensate for any positioning error occurring as the actual stopping position drifts away from said targeted stopping position due to temperature or any other factor.

A related aspect provides a controlled clutch/brake unit comprising: drive means; a driven element; clutch means operably associated with said drive means and said driven element so that when said clutch means is engaged said drive means drives said driven element; brake means operably associated with said driven element; and control means comprising means for sensing the position of said driven element at any position of said driven element, including output means, means for selecting a desired stopping position of said driven element, means for actuating said brake means to stop said driven element at said desired stopping position, including means for selecting a position at which said brake means is actuated by said actuating means, means for comparing said output means of said sensing means with said selected desired stopping position; and means for correcting said position selecting means of said brake means actuating means if said driven element is not stopped within a selected range of accuracy at the selected stopp- ing position, including means for actuating said clutch means to commence movement of said driven element.

The invention will be further described, by way of example, with reference to the accom- panying drawings, in which:

Figure 1 is a side sectional view of an index work table embodying the present invention; Figure 2 is an elevated top view of a portion of either a clutch or brake disc as utilized in Figure 1; and Figure 3 is a schematic view of the control system of the index work table.

Referring to Figure 1, an index work table apparatus 10 is illustrated having a round table 12 that can be eight feet (2.44 meters) in diameter secured to a main table drive shaft 14 operably disposed within a housing 16 and rotatable within the housing 16. The housing 16 is cylindrical, having a sidewall 17 integral with a base portion 18 and having a removable annular top portion 19 secured to the sidewall 17 by a plurality of circumfer entially spaced bolts 20. The shaft 14 and the housing 16 are appropriately interrelated with seals 21, 22 and upper and lower roller 125 bearings 23, 24 which in turn are lubricated at the lower half of the shaft by an oil reservoir 25 within the housing 16. The lower roller hearing 23 is supported by a removable lower portion 26 of the housing 16 and a radially inwardly extending annular portion 28 of the housing 16 to which the removable lower portion 26 is attached by a plurality of bolts 29. A motor 30 is directly connected to a gear reduction mechanism 32, which in turn is connected to the input of the indexing mechanism 34 via a coupling 33. The gear reducer 32 is a high ratio gear reducer, of the order of 24 to 1, and the motor 30 is intended to run continuously during the operation of the table 10. A further reduction gear mechanism 36 with approximately an 8 to 1 reduction is contained within the housing 16. A main hub 40 is shrunk fit onto the main shaft 14 at a midpoint thereof. The clutch 42 and brake 44 mechanisms are mounted directly to interact with this main hub 40. The input of the indexing mechanism 34 is a shaft 46 set in bearings 48,50 through the main housing 16 and having a bevelled pinion gear 52 at the end 54 thereof.

pinion gear 52 fits into an annular bevel gear 56 secured to an annular drive member 58 by a series of bolts 60. The drive member 58 is rotatably secured to the main shaft 14 by tapered roller bearings 62. The drive member 58 has an annular flange 64 to which a clutch disc 66, such as that illustrated in Figure 2, is securely fastened at circurnferentially disposed points thereon by dowel type screws 68. Spacers 69 are used to reduce flexure of the disc 66 during operation of the clutch 42. The clutch disc 66 sits in a recess 70 disposed in a lower part 72 of the main hub 40. The lower part 72 of the main hub 40 is secured to the main hub 40 by a series of bolts 74. Similarly, an annular brake disc 76, similar to that illustrated in Figure 2, is fixedly fastened to the upper portion 19 of the main housing 16 by a series of circumferentially spaced dowel type screws 78 and spacers 79 to reduce flexure of the disc 76 during operation of the brake 44. The brake disc 76 similarly fits between an upper hub portion 80 of the main hub 40 fixedly secured at circumferential ly spaced intervals by screws 82 to the main hub 40.

The main hub 40 further has an annular radially outwardly disposed flange 84 to guide an annular piston 86 operably disposed thereon. The piston 86 has an upper portion 88 and a lower portion 90 secured together by screws 92 and has radially inwardly disposed grooves 94 which move on splines 96 radially outwardly directed from the main hub 40. Seals 100 and 102 are also operably disposed between the outwardly disposed flange 84 of the main hub 40 and an inwardly disposed flange 104 of the lower portion 90 of the piston 86 to create an air chamber 106 for actuation of the piston. A series of circumferentially spaced recesses 107 and 108 are disposed in the piston 86 and annular flange 84 of the main hub 40, respectively, in which are disposed compression springs 110 to load 3 GB2154764A 3 the piston to operably engage the brake when movement of the index table 10 is not desired. A passage 112 is disposed through the main hub 40 into communication with a radially extending passage 114 in the main shaft 14, which in turn communicates with an axially extending passage 116 in the main shaft 14 to an inlet port 118 at the end of the main shaft 14 outside of the main housing 16. The inlet port 118 in turn communicates with a pressurized source of air (not shown). Thus, the clutch 42 and brake 44 are mechanically interlocked via the pneumatically controlled piston with the brake springs 110 set and the clutch 42 operated at 65 p.s.i. (4.48 bar) of air for full capacity in the described embodiment.

The friction discs 66, 76 for the clutch 42 and brake 44 are designed as illustrated in Figure 2 with leaves 120 between the main body 122 and the flanges 124 operably engaging the screws 68 or 78 to allow for flexure of the discs 66,76. One side of the friction disc 66 or 76 contacts the plates 72 or 80 that are dowelled into the hub 40. The other side contacts the piston assembly that is splined to the hub 40. The effect is a creation of anti- backlash torque of one-half the total torque.

The main housing 16 is filled with light oil to a level above the clutch 42. Oil is supplied to the top bearing and brake from a 1 /4 H.P. (186 watts) pump/motor combination mounted on the side of the main housing into port 130 in the housing 16.

A 5000 pulse/revolution optical encoder 132 is driven by the index table 12 through a 20/1 gear ratio reducer 134 with an antibacklash provision. This gives the controller a pulse for every.003 inch (.0076 cms) of angular motion on a workpiece diameter of 8 feet (2.44 metres), at 100,000 pulses per revolution of the work table.

Target buttons 140 are mounted on the index table 12 by a press fit in reamed holes 142. The plate 134 can be pre-bored for any combination of station numbers with the but tons 140 inserted in the correct holes for the indexing required. The target buttons 140 must have precise locations but have no parti cular reference to the work station which must also be precisely located relative to each other. Thus, any number of stations may be selected without any alteration of the com puter program of the control circuit computer 154. The work stations are mounted approxi mately mid-way between the target buttons 140. Figure 1 illustrates the target buttons energizing proximity switches 144. Prox imity switches, however, may not have the repeatability accuracy required. In this event, optical targeting may be used for even greater accuracy.

The accuracy of index is achieved through a computer learning process when the installa- 130 tion is first made or when the equipment has not operated for a period of time. It is esti mated that this learning cycle will not exceed 8 to 10 indexes.

To illustrate how the system operates, as sume a five station work table. The number of counts between stations will then be 20,000 counts (5,000 pulses times 20 (reduction gear ratio) divided by 5 stations).

On initial startup the first procedure deter mines the exact relative angular position be tween the target buttons 140 and the tar geted stopping point of the workpieces. The table 10 is moved so one of the target but tons 140 passes a proximity pickup 144. This resets the counting circuit to zero. The count ing circuit resets to zero each time a target button 140 passes the pickup. The table 10 is moved further until the workpieces are exactly in their correct targeted stopping positions. The best procedure for this is to inch the table to just short of the final targeted stopping position, to stop the main motor 30 and manually to turn the coupling 33 between the gear reducer 32 and the indexer housing 16 by hand with the clutch 42 engaged. This stopping position is locked into a memory circuit 152 (Figure 3), by actuating a key lock switch 150, as the targeted stopping position.

A digital readout of the actual count is displayed. For example, assume the count reads 9,300. The magnitude (> 5000) of that number means that the target buttons 140 are not midway between the work stations.

Simple calculations based on the load of the fixtures and workpieces indicate a stopping angle of 15 degrees in the described embodiment. 15 degrees is 100,000 times 15 divided by 360 = 4166 counts. The number 5134 (9300-4166) is then entered as the brake apply position into the brake apply memory circuit 158 (Figure 3).

An index is then initiated. Assume the actual stopping position is 8500. On the next index the computer will automatically delay the brake apply position (and brake apply memory) by 800 counts. Thus the brake will be applied at 5934 counts instead of 5134. On the next index assume the final actual stoplSing position count is 9320. The stop command for the third index would then be 5934 - 20 = 5914. This procedure continues until the actual final stopping count is 9300 (targeted stopping position) plus or minus 2 for two consecutive indexes. A signal will then be given to start the robots, etc., to operate on the workpieces on the table 10. The plus or minus 2 count error gives a positioning accuracy of plus or minus.006 inch (0.015 cms) on an eight foot (2.44 metres) diameter table 10.

Production proceeds and assume after the 15th index the count increases to 9303. On the next index the brake apply command would be at 5914 - 3 = 5911. The 4 GB 2154 764A 4 computer continues to look at the actual stopping position and continues to modify the position of the brake apply command as required. With this procedure, the effects of temperature and other factors that can cause machine drift are automatically nulled out by the computer.

Considering another possibility, assume that after running a few dozen or hundreds of parts, the operator decides a better targeted index stopping position is 9296 rather than 9300. The operator simply enters this new number as the final targeted stopping position (via the key lock switch 150), proceeds through a few learning indices, and resumes production.

At present it is visualized that whenever the equipment is stopped more than approximately 30 minutes, a learning cycle would be required. A temperature transducer may also be included with the control system. Monitoring temperature as a modifier for the brake apply command may eliminate the learning cycles except for extended stopping periods.

The microcomputer and ancillary logic is powered by a nickle-cadmium battery with an on-board charger to isolate any deleterious spikes in the power grid.

A schematic diagram of the control circuit is shown in Figure 3. The counter 132 is reset to zero every time a target button 140 passes a sensor 144, but otherwise counts pulses in response to movement of the table 12. When the workpiece has been placed in the targeted stopping position, the key lock switch 150 is activated to lock the selected count at this position into the memory circuit 152 of the microprocessor or microcomputer 154. A comparator 156 within the microcomputer 154 compares the current count from the counter 132 with the count locked into the memory circuit 152 to determine positioning accuracy. After the calculations (described above) have been made, the brake application count is also placed into the brake apply memory circuit 158 of the computer. This count is also transmitted to a comparator 160 (which may or may not be the same as comparator 156). When the counter 132 reaches the count stored in the brake apply memory circuit 158, the brake 44 is applied. The workpiece and table 12 will stop, at which point that count is compared to the targeted stopping position in the memory lock circuit 152. If the comparison is within the range (plus or minus 003) selected (YES), a signal is given to the robot or other machine to commence operation. At the completion of the operation, the robot or machine signals the clutch 162 to index to the next station. If the comparison is not within the range (NO), the clutch actuator indexes again and the computer modifies the brake application count difference between actual and desired).

CLAIMS 1. A controlled clutch/brake unit for use in a work operation comprising drive means; a driven element; clutch means for operably associating said drive means with said driven element when said clutch means is engaged; brake means; and means for controlling said clutch and brake means to control the position of said driven element, including means for setting a zero point, means for actuating said brake to stop said driven element, means for learning in what position the driven element is stopped relative to said zero point, means for learning what movement of said driven element has to be made to attain a selected target stopping point set relative to said zero point, means for self-correcting any error be- tween an actual stopping position of said driven element and said target stopping point until the desired target stopping point has been attained within a selected range of accuracy, and means for continued correction of any error between an actual stopping position of said driven element and said targeted stopping position as the work operation progresses in order to automatically compensate for any positioning error occuring as the ac- tual stopping position drifts away from said targeted stopping position due to temperature or any other factor.
2. A clutch/brake unit as claimed in claim 1, wherein said controlling means further comprises means for changing the target stopping point as desired.
3. A clutch/brake unit as claimed in claim 1 or 2, further comprising battery means for powering said controlling means and charger means for said battery means.
4. A controlled clutch/brake unit comprising: drive means; a driven element; clutch means operably associated with said drive means and said driven element so that when said clutch means is engaged said drive means drives said driven element; brake means operably associated with said driven element; and control means comprising means for sensing the position of said driven element at any position of said driven element, including output means, means for selecting a desired stopping position of said driven element, means for actuating said brake means to stop said driven element at said desired stopping position, including means for selecting a position at which said brake means is actuated by said actuating means, means for comparing said output means of said sensing means with said se- lected desired stopping position; and means for correcting said position selecting means of said brake means actuating means if said driven element is not stopped within a selected range of accuracy at the selected stopping position, including means for actuating in the brake apply memory circuit 158 as described above (adding or subtracting the 130 GB 2 154 764A 5 said clutch means to commence movement of said driven element.
5. A clutch/brake unit as claimed in claim 4, further comprising means for associating a workpiece with said driven element, and means for controlling the operation of a device capable of performing desired work on said workpiece.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1985, 4235. Published at The Patent Office. 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.