US2890590A - Index head - Google Patents

Description

A. F. O'HARAH INDEX HEAD Filed April 3, 1958 June 16, 1959 INVENTOR. fl pa? 0 9 M than INDEX HEAD Alvin F. OHarah, Erie, Pa., assignor to Castle Machines, Incorporated, Erie, Pa., a corporation of Pennsylvania Application April 3, 1958, Serial No. 726,213

4 Claims. (CI. 74-88) In the indexing of turntables, substantial forces are required to move turntable between successive index positions and difliculty has been experienced with rebound forces which interfere with the accuracy of the indexing. It has also been difficult to change the speed of indexing and the indexing stroke. The present invention is intended to overcome the difficulties by an index head which is positively held at each index position and is moved to a succeeding index position by a piston which can readily be controlled for any time cycle. The positive positioning of the index head is through a rotary cam which also has a drive gear for driving the turntable. With this index head, the timing of the indexing is by controlling the piston and the angle through which the turntable is moved at each stroke of the piston is controlled by the gear ratio from the rotary cam. This provides a high degree of flexibility both in the time interval between indexing steps and in the angular movement of each step.

In the accompany drawing, Fig. 1 is a top plan view partly broken away of an index head; Fig. 2 is a section on line 2-2 of Fig. 1; and Fig. 3 is a bottom view of the cam driver.

The index head is actuated by a double acting cylinder I mounted on a frame 2 and having a piston rod 3 connected to a connecting rod 4 through a pivot pin 5. The connecting rod is biased in a counterclockwise direction as viewed in Fig. 1 by a spring 6 surrounding the pivot 5. At the outer end of the connecting rod is fixed an upwardly projecting pin 7 which rides in an endless groove 8 on the under side of a cam driver 9. The groove has three (or more) equal length sides forming a triangle (or polygon) centered on the axis of the cam driver. At the three corners of the triangle and on the upper side of the cam driver are fixed three upwardly extending pins 10. These pins need not be directly above the corners of the triangle, it only being essential that the space between any two pins be equal to the chord distance between the ends of adjacent radial slots 11 in a cam 12. There are as many pins as there are sides of the cam groove.

The cam driver 9 is journaled on a stub shaft 13 mounted in the frame and the cam 12 is fixed to a shaft 14 journaled at 15 in a cross member 16. While the shaft 14 is shown on the center line of the driving cylinder 1, it could be moved from that position in which case the relative position of the drive pins 10 on the cam driver 9 and the drive slots 11 in the cam 12 would be changed.

On the projecting end of the shaft 14 is a pinion 16 which meshes with a gear 17 journaled on an upwardly projecting shaft 18 on an eccentric 19. By turning the eccentric in the frame, the center distance between the shafts 14 and 18 can be adjusted. Upon reaching the selected position, the eccentric is locked in place by a wedge clamp 20. The gear 17 is the output gear which drives the table to be indexed. The angular movement of the table can be varied by changing the ratio of the ice gears 16 and 17 which is possible over a wide range due to the adjustment permitted by the eccentric shaft 18. This permits the use of a turntable with difiierent numbers of index stations without making any other changes than the gear ratio of the gears 16 and 17. This is an important advantage in production machinery where different numbers of work fixtures are frequently mounted on the same turntable and the possibility of equally spacing these fixtures eliminates the idle stations frequently found in turnables.

The index head is shown with the parts in position to start an index operation. In this position it willl be noted that two pins 10 on the upperside of the driver cam 9 fit in the open ends of radial slots 11 in the cam 12. In this position forward or backward movement of the cam 12 is only possible by turning of the driver cam 9. It will be noted that any force exerted by the cam 12 on the pin 10 which is lowermost in Fig. 1 will act on a center line connecting that pin and the shaft 13 on which the driver cam 9 is journaled. Accordingly, there can be no torque transferred from the cam 12 to the cam 9 by any force coming from the index driving gears 16 and 17. This means that re bound forces on the turntable cannot change the index position. This is an important advantage in high speed indexing. A still further safeguard against backward movement of the index is provided by a spring biased blocking member 21 cooperating with the upper pin 10 received in a slot 11. For the upper pin 10 to leave the slot 11 in which it is engaged, it would be necessary that the driver cam 12 turn in a counterclockwise direction as viewed in Fig. 1. This turning movement is positively resisted by the blocking member 21 which is rigidly stopped in the position illustrated although it can pivot to theright so as to permit the pin 10 to enter the slot 11. The blocking member 21 is still further insurance against inaccuracy of indexing caused by rebound forces.

At the start of the indexing operation, air is admitted to the cylinder 1 causing the piston 3 to move to the left. At the start of this movement, the pin 7 on the connecting rod 4 is held by the spring 6 in an offset section 22 in the cam groove 8. The initial force of the connecting rod is transmitted to the driver cam 9 with maximum torque which is desirable for rapid acceleration of the turntable. The pin 7 remains in this off-set section 22 causing the cam 9 to turn in a clockwise direction as viewed in Fig. 1 until the cam 9 has turned degrees. At this point, the pin 7 will occupy the position indicated by the numeral 23 and the cam 12 will have turn 60 degrees so that the driving pin 10 which was uppermost at the start of the index operation is now lowermost and a different pin has entered the uppermost slot 11. Over-travel is prevented by a stop 24 limiting the stroke of the connecting rod 4. Also, at the end of the stroke, the connecting rod is close to dead center and preferably slightly beyond dead center so that the torque tending to cause over-travel is very slight. Furthermore, the piston itself has limited travel in the cylinder although it is preferable to use the external stop 24 because that can be more readily adjusted.

The indexing movement of the cam 12 starts slowly as the uppermost pin enters its associated slot 11, accelerates gradually, increases to maximum speed at the mid-position and then, decelerates as the pin 10 which was uppermost at the start of the indexing operation approaches the lowermost position.

What is claimed as new is:

1. An index head comprising a piston and connecting rod, a cam driver journaled in a frame, a crank pin on the connecting rod, an endless groove in the cam driver receiving the crank pin, said groove having equal length angularly spaced sides forming a polygon centered on the axis of the cam driver, a notch at the end of each side of the groove orientcdto. be yqsitively engaged by the crank pin on the, forward stroke of the piston and to release the crank pin upon the. return stroke of the piston, drive pins on the cam driver having the same angular spacing as the sides of the polygon, and a driven cam journaled on an axis spaced from the axis of the cam driver and having angularly spaced radial slots therein open at the outer ends and positioned so that in each index position a pair of adjacent slots receive a, pair of adjacent drive pins, the chordwise distance between the open ends of adjacent slots being equal to the chordwise distance between adjacent drive pairs, one of. the slots; in each index position having sides normal to a center line between the drive pin in that slot and the axis of the cam driver, and drive gearing connected to the driven cam.

2. An index head comprising a piston and connecting rod, a cam driver journaled in a frame, a crank pin on the connecting rod, an endless groove in the cam driver receiving the crank pin, said groove having equal length angularly spaced sides forming a polygon centered on the axis of the cam driver, means holding the crank pin in fixed relation to the groove on the forward stroke of the piston and releasing the crank pin upon the return stroke of the piston, drive pins on the cam driver having the same angular spacing as thesides of the polygon, and a driven cam journaled on, an axis spaced from the axis of the cam driver and having angularly spaced radial slots therein open at the outer ends and positioned so that in each index position a pair of adjacent slots receive a pair of adjacent drive pins, the chordwise distance between the open ends of adjacent slots being equal to the chordwise distance between adjacent drive pairs, and-drive gearing connected to the driven cam.

3. An index head. comprising a piston and connecting rod, a cam driver journaled in a frame, a crank pin on the connecting rod, anendless groove in, the cam driver receiving the crank pin, said groove having equal length 4 angularly spaced sides forming a polygon centered on the axis of the cam driver, a notch at the end of each side of the groove oriented to be positively engaged by the crank pin on the forward stroke of the piston and to release the crank pin upon the return stroke of the piston, drive pins on the cam driver having the same angular spacing as the sides of the polygon, and a driven cam journaled on an axis spaced from the axis of the cam driver and having angularly spaced radial slots therein open at the outer ends and positioned so that in each index position a pair of adjacent slots receive a pair of adjacent drive pins, the chordwise distance between the open ends of adjacent slots being equal to the chordwise distance between adjacent drive pairs, and drive gearing connected to the driven cam.

4. An index head comprising a piston and connecting rod, a cam driver journaled in a frame, a crank pin on the connecting rod, an endless groove in the cam driver receiving the crank pin, said groove having equal length angularly spaced sides forming a polygon centered on the axis of the cam driver, a notch at the end of each side of the groove oriented to be positively engaged by the crank pin on the forward stroke of the piston and to release the. crank pin upon the return stroke of the piston, drive pins on the cam driver having the same angular spacing as the sides of the polygon, and a driver cam journaled on an axis spaced from the axis of the cam driver and having angularly spaced radial slots therein open at the outer ends and positioned so that a pair of adjacent slots. receive a pair of adjacent drive pins, the chordwise. distance between the open ends of adjacent slots being equal to the chordwise distance between adjacent drive pairs, a pivoted stop opposite one otthe slots in each index position and blocking reverse movement No references cited.

Images