Hydraulic positioner for large and heavy work pieces

Abstract

A heavy duty hydraulic positioner has headstock and tailstock carriages to support large and heavy work pieces to be processed in a manufacturing operation, such as robotic welding. Each carriage is independently movable along a column, and has a hard stop associated with each pre-program workpiece position, thereby providing accurate repeatability. Repeatability is further enhanced by linear, noncontact absolute encoders for the elevation axes of the headstock and tailstock, and rotary, noncontact absolute encoders for the rotary axes of the headstock and tailstock.

Claims

1. A positioner for raising, lowering and rotating a work piece, comprising: a first vertical column and a first carriage movable along the column; a second vertical column and a second carriage movable along the second column; first and second linear actuators operatively connected to the first and second carriages, respectively, to move the carriages along the columns; a PLC to control movement of the carriages along the columns, and having control software with a plurality of preprogrammed positions for the headstock and tail stock; a rotatable headstock on the first carriage; a rotatable tailstock on the second carriage; the first carriage having a plurality of teeth, with each of the teeth corresponding to one of the preprogrammed positions; and the first column having a stop member to engage one of the teeth to retain the first carriage at a selected position on the first column.

2. The positioner of claim 1 further comprising a rotary encoder on the headstock.

3. The positioner of claim 2 wherein the rotary encoder is non-contact.

4. The positioner of claim 1 wherein the linear actuators are single acting hydraulic cylinders.

5. The positioner of claim 4 wherein each hydraulic cylinder includes a dynamic electronic proportional control valve.

6. The positioner of claim 5 wherein each hydraulic cylinder includes a linear absolute encoder.

7. The positioner of claim 4 wherein each hydraulic cylinder includes a linear absolute encoder.

8. The positioner of claim 1 wherein the stop member is a hinged plate.

9. The positioner of claim 1 wherein the head stock and tail stock are independently movable.

10. The positioner of claim 9 wherein the stop member includes a solenoid to retract the plate from a stop position engaging one of the teeth.

11. The positioner of claim 1 further comprising encoders on the carriages to verify positions of the headstock and tailstock.

12. The positioner of claim 1 wherein each carriage includes a position window and an encoder to sense the position of the respective head stock and tail stock via the position window.

13. The positioner of claim 1 wherein the second column has a stop member to engage one of the teeth to retain the second carriage in a selected position.

14. A method of positioning a headstock and a tailstock on a first and second columns, respectively, to hold a work piece for a manufacturing process, comprising: setting the headstock and tailstock in a home position; raising a carriage supporting one of the headstock and tailstock until a tooth member on the carriage representing a pre-programmed hard stop position passes a stop member on one of the columns supporting the carriage; moving the stop member into a vertical path of the tooth; and then lowering the carriage until the tooth engages the stop member.

15. The method of claim 14 further comprising rotating the work piece about axes on the head stock and the tail stock.

16. The method of claim 14 further comprising verifying the pre-programmed hard stop position using an encoder.

17. The method of claim 14 further comprising controlling raising and lowering of the carriage with PLC software having a plurality of hard stop positions.

18. The method of claim 14 further comprising controlling raising and lowering with a hydraulic cylinder having a dynamic electronic proportional control valve.

19. The method of claim 14 further comprising controlling raising and lowering with a hydraulic cylinder having a linear absolute encoder.

20. The method of claim 14 further comprising independently raising and lowering the headstock and tailstock.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view showing the hydraulic positioner of the present invention, including the master headstock column and the slave tailstock column, with the headstock shown in a solid line lowered position and a broken line raised position.

(2) FIG. 2 is the side elevation view of the positioner columns.

(3) FIG. 3 is a partially exploded view of the positioner columns.

(4) FIG. 4 is an enlarged view showing the hard stop components on the headstock column.

(5) FIG. 5 is a perspective view of the headstock carriage.

(6) FIG. 6 is a sectional view of one of the columns showing the internal hydraulic cylinder.

(7) FIG. 7 is an enlarged view showing the stop plate in a retracted position and an extended position.

(8) FIGS. 8A-8D are schematic side elevation views showing the tailstock carriage in various elevated positions.

(9) FIG. 9 is a hydraulic schematic for the headstock.

(10) FIG. 10 is a hydraulic skematic for the tailstock.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) The hydraulic positioner of the present invention is generally designated by the reference numeral 10 in the drawings. The positioner 10 includes a headstock column 12 and a tailstock column 14 which are spaced apart so as to receive a workpiece (not shown) between the columns. The headstock column 12 includes a headstock carriage 16, and the tailstock column 14 includes a tailstock carriage 18. Each carriage 16, 18 can be raised and lowered by a hydraulic cylinder 20 mounted within the respective column 12, 14. A fluid reservoir 22 and a hydraulic motor pump 24 is provided on each column 12, 14 for moving the carriages 16, 18. A cover 26 detachably mounts to each column 12, 14 so as to enclose the reservoir 22 and pump 24.

(12) A headstock 28 is rotatably mounted on the headstock carriage 16, and a tailstock 30 is rotatably mounted on the tailstock carriage 18. A hydraulic motor 32 is provided for each of the headstock 28 and tailstock 30 for rotation in clockwise and counterclockwise directions. The headstock 28 and tailstock 30 each include a mounting plate with a slew bearing and a rotary hydraulic slew drive 32 with a self-locking worm drive. A limit switch 34 is operatively connected to each of the headstock 28 and tailstock 30. A flex chain 38 is also provided on each of the columns 12, 14 for management of the various cables of the positioner 10.

(13) The above description of the positioner 10 is conventional.

(14) One novel feature of the positioner 10 is the provision of a hard stop for all programmed positions for improved repeatability. More particularly, the hard stop system includes a plurality of teeth 40 on each column 12, 14, as best shown in FIG. 5. A plate 42 is hinged to each column. A solenoid 44 is operatively connected to each hinge plate 42 and to the PLC (programmable logic controller) 45 (FIG. 6) inside the control panel 54 mounted on the tower 12 of the positioner 10.

(15) In the preferred embodiment, adjacent teeth are spaced approximately 2.5 inches apart. Before one of the carriages 16, 18 is raised from a lowered home position, the PLC actuates the solenoid to 44 to retract the hinged plate 42 out of the path of the teeth, as shown in solid lines in FIG. 7. The carriage 16 and/or 18 is then raised to a position so that the tooth associated with the programmed position is slightly above the hinge plate 42. The solenoid 44 is then actuated to pivot or extend the plate 42 beneath the program position tooth, as shown in broken lines in FIG. 7. The carriage 16, 18 is then lowered such that the tooth engages the hinged plate 42, thereby creating a hard stop for the carriage 16, 18. In order to lower the carriage 16, 18, the process is reversed. The carriage 16, 18 is raised sufficiently so that the solenoid can retract the hinged plate 42 from the programmed position tooth, and then the carriage can be lowered in a controlled manner by the hydraulic cylinder 20.

(16) Another unique feature of the present invention is the utilization of electronic proportional control valves 46 in the hydraulic fluid circuitry, which provide improved motion control and repeatability. The control valves 46 replaces conventional low and high-volume fluid valves.

(17) A further new feature of the present invention is the use of linear, non-contact, absolute encoders 48 in conjunction with the carriage elevation axes. These encoders 48 have magnetostrictive position sensing.

(18) The combined benefits of the proportional control valves 46 and the absolute encoders 48 provide positional data and the motion control necessary to implement the hard stop feature while eliminating vertical location variability of the headstock 16 and the tailstock 18.

(19) Another improved feature for the positioner 10 is the utilization of rotary non-contact, absolute encoders 50 in close proximity and adjacent to the slew drive face plate and fixture mounting plate of the headstock 28 and tailstock 30. These encoders for the rotary axes improve the rotary axis repeatability from +/0.250 inch to +/0.030 inch.

(20) The absolute encoders 46, 48 for all positioner axes allow each axis to immediately recover from power outages without recalibration. For the elevation axes of the carriages 16, 18, the combined improved fine motion control and improved position information allows the control system to make subtle position adjustments that assure reliable, controlled landing on the hard stop teeth 40. Locating the elevating axis to the hard stop teeth improves machine and operator safety.

(21) In operation, the headstock 28 and tailstock 30 can be independently elevated to different programmed positions so as to provide an angular tilt to the workpiece supported between the headstock and tailstock. The headstock 28 and tailstock 30 can also be rotated in unison in either the clockwise or account counterclockwise directions so as to rotate the workpiece.

(22) FIGS. 6A-6D schematically illustrate operation of one of the column 14, with operation of the column 12 being the same. The carriage 18 starts in a lowered home position, as shown in FIG. 6A. The tooth labeled 40P corresponds to the desired program position for the carriage. As the carriage rises (FIG. 6B), the teeth 40 push the hinge plate 42 upwardly for clearance. As the hinge plate 42 passes each tooth 40, the hinge drops back into a safety position beneath the adjacent upper tooth. When they linear encoder 48 senses the count window 52 on the carriage, the PLC terminates extension of the cylinder so that the hinge plate 42 is positioned beneath the target position tooth 40P (FIG. 6C). The PLC then causes the cylinder to retract, thereby lowering the carriage until the target tooth 40P engages the plate 42 for a hard stop with the carriage in the desired programmed position (FIG. 6D).

(23) FIGS. 9 and 10 show the hydraulic circuitry for the headstock and tailstock, respectfully. This circuitry allows the utilization of cost effective fixed displacement hydraulic power units for the positioner, while introducing an external electro-proportional flow valve to fine tune the hydraulic flow rates for the extension and retraction of the vertical hydraulic cylinders and for rotation of the hydraulic motors in the columns. The flow control valve will be controlled by a proportional valve amplifier, which interprets a 0-10 VDC and a log command signal from the PLC and control electrical power to the proportional solenoid coil via a 4-20 mA command signal. The amplifier also provides the capability of programming ramp-up and ramp-down features, as needed. By pairing this hydraulic circuitry with the linear position feedback into the PLC, the headstock and tailstock vertical powered elevation speed and gravity can be independently controlled. This improved programmed location control provides for more precision movement of the work piece.

(24) More particularly, the hydraulic circuitry for the head stock and tail stock both include a hydraulic unit component 60 including an electric motor 62, a gear pump 64, a relief valve 66, and a check valve 68. Each of the headstock and tailstock hydraulic circuits also includes an electro-proportional flow manifold 70 having a two-way, normally closed valve 72, a bypass valve 74, and a proportional throttling, normally closed valve 76. The circuitry for the headstock also includes a directional control manifold 80, having a 3-way, 2-position valve 82 and a 4-way, 2-position valve 84, which is not present in the tailstock circuitry. A 2-way, normally closed valve 78 is also provided for each of the hydraulic cylinders 20 in the headstock and tailstock.

(25) The invention has been shown and described above with the preferred embodiments, and it is understood that many modifications, substitutions, and additions may be made which are within the intended spirit and scope of the invention. From the foregoing, it can be seen that the present invention accomplishes at least all of its stated objectives.