CNC MACHINING SYSTEM

Abstract: A bore slotting machine for cutting radially spaced longitudinal slots in sleeves for automotive power steering units comprising a cutting face adapted to operate within a bore of a component being worked; a motorised drive adapted to impart reciprocating motion to the cutting face; a positional feedback associated with the cutting face (10) and adapted to communicate with a computer; a chuck (12) adapted to hold a component being worked at a location adjacent the cutting face (10) and being supported for indexible rotational movement about a Y axis, substantially parallel to that of the bore in the component being worked; a first shuttle carriage (4) carrying the workholding device such shuttle being adapted for linear motion perpendicular to the bore axis of the component under the influence of a first servo drive (7); a second shuttle carriage (14) adapted to carry the cutting face (10) and associated motorised drive such that movement of the second carriage (14) achieves liner reversible relative motion between the component being worked and the cutting face (10) along an axis parallel to the bore axis; a second servo drive (15) for actuating the second shuttle carriage (14); a controlling computer for activating the cutting face drive and synchronising the first (7) and the second (15) servo drives with the position of the cutting face (10); each drive having a closed loop control system incorporating a feedback device.

Description: CNC MACHΓJSΓLNG SYSTEM The present invention relates to bore slotting machinery and in particular to apparatus of the type utilising a reciprocating cutting face to produce one or more longitudinal slots in the bore of a component. For many years various apparatus have been proposed for cutting longitudinal slots in the bores of relatively small sleeves such as those utilised in automotive rotary power steering valves. The design of such machinery necessarily involves relative movement between the cutting face and the component being worked along and about multiple axes; precision synchronisation of the high speed movements relative to the various axes being of critical importance. In addition to the synchronised movements required to achieve the actual cut the cutting face of the tool and/or the workholding member must be capable of movement to facilitate loading and unloading of the workholding member without interference with the cutting face. To date a number of mechanical arrangements have been proposed in order to achieve the high speed synchronised relative movement between a workholding member and the cutting face necessary for the cutting operation and also to facilitate relative displacement of the component for loading and unloading during both the cutting and loading/unloading operations. It is the object of the present invention to provide an alternate bore slotting machine which utilises computer controlled servo drives to control and synchronise at least some of the relative motions between the cutting face and the workholding member. The term "servo drive" where used throughout this specification is intended to encompass any type of servo driven motor or actuator including conventional motors, servo motors, linear motors, hydraulic activators, pneumatic linear actuators and rotary actuators. The use of a servo drive system as opposed to mechanical configurations to control bore slotting machinery is particularly advantageous as it has been found that comparable speeds may be obtained to those achieved by mechanically synchronised equipment whereas electronically synchronised equipment eliminates the need for complicated mechanical linkages and is not subject to the wear rates and associated frequent service requirements of mechanically synchronised equipment. Electronically synchronised bore slotting machinery is furthermore better adapted for situations where components of different dimensions are to be produced having regard to the fact that the CNC parameters may be programmed, stored and recalled far more quickly than replacement, adjustment and/or alteration of mechanical components comprising the system. In addition, greater accuracy of the position, size and surface finish of the generated slots may be achieved because of the mechanical simplicity of the servo controlled machinery, and the ability to use feedback to compensate for variation and imperfections in the machine elements. According to the present invention there is provided a bore slotting machine comprising a cutting face adapted to operate within a bore of a component being worked; a motorised drive adapted to impart reciprocating motion to the cutting face; an electronic positional feedback device associated with the cutting face; a workholding device adapted to hold a component being worked at a location adjacent the cutting arm and being supported for indexible rotational movement about a Y axis substantially parallel to that of the bore in the component being worked; a first shuttle carriage carrying either the workholding device or the cutting face such shuttle being adapted for linear motion perpendicular to the bore axis of the component under the control of a servo drive; a second shuttle carriage adapted to carry parts of the machine such that movement of the carriage achieves linear reversible relative motion between the component being worked and the cutting face along an axis parallel to the bore axis; a second servo drive for actuating the second shuttle carriage; computer control means for activating the first and second servo drives and synchronising the two drives; each drive having a closed loop computer control system incorporating a feedback device. One embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure I is a perspective view of a machine in accordance with the present invention; Figure II is an exploded perspective view of part of the machine of figure I. The embodiment of figure I depicts a CNC machining system having a base 1 with an upstanding column 2 extending thereabove. Upstanding column 2 is provided with guide rails 3 adapted to constrain a first shuttle carriage 4 for a range of reversible vertical movement under the influence of drive shaft S operated by linear electric servo drive 6. Electric servo drive 7 is mounted to shuttle carriage 4 via an appropriate translatory crank mechanism (not shown) adapted to impart oscillatory reversing rotational movement to spindle 8 and angular reciprocating motion to cutting arm 9 and cutting face 10. As may best be viewed from figure II the sleeve 11 being worked is held in chuck 12 mounted in turn to spindle 13. Spindle 13 is mounted on a second shuttle carriage 14 and is capable of being rotated about a "Y" axis by servo drive 15 and intermediate worm drive 16. Closed loop control of servo drive IS is facilitated by feedback device 17 being a rotary encoder. Shuttle carriage 14, servo drive IS, chuck 12 and hence the sleeve 11 being worked are all supported for reversible linear travel along axis X by rails 18 under the influence of electric servo drive motor 19 and ball screw drive shaft 20. It will be appreciated that the reciprocating arcuate travel of cutting arm 9 imparts reciprocating arcuate travel to cutting face 10. In order that this arcuate travel of cutting face 10 is capable of cutting slots aligned with axis Y in the bore of sleeve 11 a fast reciprocating motion must be imparted to shuttle carriage 14 in order to maintain full relief of the cutting head 10 from the work face in the bore of sleeve 11 during the return stroke of the cutting arm as opposed to the cutting stroke. For each cutting stroke the cutting head must be advanced to a new position and held stationary for the full duration of engagement of the cutting face in the bore. This reciprocating motion of shuttle carriage 14 must be synchronised with the oscillating arcuate movement of cutting face 10 to maintain the correct relative position profile and hence there is common computer control (not shown) of the two drives. The control of these servo drives is also of a closed loop nature such that feedback devices constantly input to the controlling computer the position of the components controlled by the respective drives. Drive 19 is also responsible for moving chuck 12 and hence sleeve 11 from the working position depicted in unbroken lines in figure I to the loading and unloading position depicted in broken lines at 21 in figure I. It will furthermore be appreciated that servo drive 19 by way of its control of shuttle 14 is also responsible for controlling the depth of cut for the slot (not shown) being formed by cutting face 10 in the bore of sleeve 11 and hence drive 19 is responsible for advancing sleeve 11 onto cutting face 10 during the cutting operation. Electric servo drive motor 15 is responsible for determining the radial position of the slot (not shown) being cut by cutting face 10 in sleeve 11 as it controls via worm drive 16 and chuck 12 rotation of sleeve 11 relative to cutting face 10. Once again this motion must be synchronised with that of servo drives 7 and 19. Synchronisation is best achieved by way of common computer control and closed loop control of each drive facilitated by feedback devices (only one shown at 17). Typically a number of radially separated slots parallel with axis Y" would be cut in sleeve 11 and drive 15 would control the radial separation of the slots. The rotation of chuck 12 by electric servo drive motor 15 not only determines the radial displacement of one slot from an adjacent slot but also achieves compensation for any lack of concentricity in the sleeve identified during a probing operation performed by the machine prior to the cutting operation. The aforementioned probing operation will now be described hereafter although it is not depicted in the drawings. The probing operation will be familiar to any person skilled in the art of machining circular objects which need to have controlled runout in order that the finished product may fall within acceptable concentricity ranges. A sleeve being worked is loaded onto an input conveyor with its axis in a vertical orientation. The input conveyor then carries the sleeve to a loading station where the sleeve is transferred from the conveyor to a pick-up nest. A four position indexing unit fitted with gripper arms lowers, grips the sleeve, raises, then indexes ninety degrees to the probe station where it lowers, releases the sleeve, then raises away from the probe station. At the probe station the sleeve is clamped within a collet. The collet is then rotated, via a toothed belt drive, until the hitch pin hole is located and positioned via a photo-electric cell. The sleeve is then maintained in this orientation for probing before loading into the machining station. After orientation, the probe unit lowers and measures the runout of the sleeve bore relative to the O.D. of the sleeve and the hitch pin hole position. This data is then stored in the control computer for later use in cutting position compensation during the machining operation. It will be appreciated that once the concentricity information has been obtained with respect to a particular component in the conventional manner above described the information may readily be incorporated into the programming of the control computer such that chuck IS may be rotated prior to the cutting operation so as to ensure that all slots which are cut are radially aligned with the centre of the bore of the component as compared with the actual centre of the clamping axis. The clamping axis is related to the external surface of a component as well as the axis about which the chuck rotates. Compensation in this manner may result in slots on one side of the sleeve being slightly deeper than slots on the other side of the sleeve although this is of little consequence in relation to many components which are manufactured by the subject machinery and in particular power steering sleeves for automobiles. It is more important that the radial disposition of the slots is true to the internal bore dimensions of the component rather than to have slots of precisely the same depth. Electric servo drive motor 6 is responsible for removing cutting face 10 from sleeve 11 to facilitate loading of fresh sleeves to be worked and unloading of worked sleeves. In the case of some longer slots it is also necessary to move first shuttle carriage 4 as the cutting of each individual slot progresses in order that the cutting face may be imparted with adequate reach for the desired length of slot. It is therefore desirable that drive 6 is similarly linked to a common computerised control unit (not shown) to that controlling drives IS, 19 and 7 in order that the cutting action may proceed in each sleeve and from sleeve to sleeve. Once again closed loop computer control is utilised with a feedback device (not shown) imparting control over the precise position of the cutting face at any time. The applicant has found that the Siemens Sinumerik 840 C TM range of CNC controllers are appropriate for controlling the electronic servo drives utilised in the abovementioned embodiment and that, rather than conventional CNC programming, interpolation and compensation with tables is utilised with the spindle axis as the master axis and the remaining drives configured as slave axes. In this manner the table of relationships between slave function positions and master function positions may be loaded into the computers memory prior to the running of the programmed cycle as opposed to such information being progressively loaded during the cycle as is the case in normal CNC programming. Far superior processing speed is thereby achieved. Block cycle times of 4.0 milliseconds have been utilised with interpolation clock cycles of 4.0 milliseconds, position control cycles of 1.0 millisecond and drive basic cycle times of 0.5 milliseconds. For simplicity figure I does not include detail of ancillary equipment necessary for operation of bore slotting machinery such as apparatus for loading and unloading sleeves from the chuck and for removing cutting material.

Claims: The claims defining the invention are as follows: 1. A bore slotting machine comprising a cutting face adapted to operate within a bore of a component being worked; a motorised drive adapted to impart reciprocating motion to the cutting face; a positional feedback device associated with the cutting face and adapted to communicate with a computer; a workholding device adapted to hold a component being worked at a location adjacent the cutting face and being supported for indexible rotational movement about a Y axis substantially parallel to that of the bore in the component being worked; a first shuttle carriage carrying either the workholding device or the cutting face such shuttle being adapted for linear motion perpendicular to the bore axis of the component under the influence of a first servo drive; a second shuttle carriage adapted to carry part of the machine such that movement of the second carriage achieves linear reversible relative motion between the component being worked and the cutting face along an axis parallel to the bore axis; a second servo drive for actuating the second shuttle carriage; computer means for controlling the cutting face drive and synchronising the first and second servo drives with the position of the cutting face; each drive having a closed loop control system incorporating a feedback device. 2. A bore slotting machine in accordance with claim 1 hereof wherein each drive has a closed loop control system incorporating a feedback device. 3. A bore slotting machine in accordance with claim 1 wherein the reciprocating motion of the cutting face is angular reciprocating motion about an axis perpendicular to the bore of the component being worked. 4. A bore slotting machine in accordance with claim 1 wherein the reciprocating motion of the cutting face is linear reciprocating motion along an axis parallel to that of the bore of the component being worked. 5. A bore slotting machine in accordance with any one of the preceding claims wherein the first shuttle carriage carries the workholding device and the second shuttle carriage carries the cutting face and associated motorised drive. 6. A bore slotting machine in accordance with claim 1 hereof wherein the indexible rotational movement of the workholding device about the Y' axis is imparted by a third servo drive under the control of the computer means and synchronised to at least the cutting face drive thereby. 7. A bore slotting machine in accordance with any one of the preceding claims wherein the computer means controls the servo drives by way of a program utilising the cutting drive as the master drive with the remaining drive or drives as slave drives. 8. A bore slotting machine in accordance with any one of the preceding claims wherein the computer control for the servo drives utilises interpolation and compensation with tables with the cutting face drive as the master drive and the remaining drive or drives as slaves. 9. A bore slotting machine in accordance with any one of the preceding claims wherein the first servo drive comprises a linear electronic motor drive. 10. A bore slotting machine in accordance with any one of the preceding claims wherein the servo drive means for the second shuttle carriage axis is a linear motor. 11. A bore slotting machine in accordance with any one of the preceding claims wherein there is provided a runout measuring probe capable of determining any differences between the external clamping diameter of the component being worked and the internal bore diameter of the component; means for transferring such runout information to the computer means; means for adjusting the rotational movement of the workholding device in response to the runout information to ensure that the radial disposition of slots being cut in the bore is referenced to the centre of the bore of the component rather than the centre of the external clamped dimension of the component.

Inventors: FRECKER PAUL, KUENZLE MARK, NEMETH FRED, FRECKER, PAUL, KUENZLE, MARK, NEMETH, FRED
Applicants: FRECKER PAUL, KIRBY JAMES N PTY LTD, KUENZLE MARK, NEMETH FRED, FRECKER, PAUL, JAMES N KIRBY PTY. LTD., KUENZLE, MARK, NEMETH, FRED
Application year: 1995
Main classification: B23D1
IPC codes: B23D3, B23D5