WO1993006954A1 - Improvements to punch presses - Google Patents

Abstract

A punch press is provided with rotors (25, 27) for rotating a punch tool (12) relative to the punch ram (10) on which it is removably mounted. The rotors are rotated by worm gear (30) which is driven by a servo motor (34) via a flexible drive (35). An improved control strategy is used for the flexible drive. A stripper plate (20) is constrained to rotate with the tool but is movable axially relative thereto. A retractable rotor (42) also rotates the removable die (40). Clamps (17, 37, 55) are used to clamp the tool, stripper and die, respectively. The punch tool and die can be rotated, interdependently or independently, to provide continuous adjustment or to perform operations such as drilling, reaming. A single die (90) can be used for multiple staged or progressive operations. The punch tool may comprise multiple punch pins (66) which are selectable by rotation of the tool. The punch press is provided with pivotable work clamps (80) which compensate for distortion of the workpiece. The work clamps are relocatable automatically.

Description

"IMPROVEMENTS TO PUNCH PRESSES" THIS INVENTION relates to improvements to punch presses, such as punch presses of the type described in U.S. patent no. 4,823,658. 5 BACKGROUND ART

* Punch presses are commonly employed to punch holes in metal sheet and plate, and for this purpose, most punch presses comprise a C-shaped frame having a vertical punch head assembly positioned over a die. A 10 punch ram is mounted for reciprocating motion within the punch head assembly, and a punch tool is normally detachably mounted at the end of the punch ram. In use, the sheet, plate or other wor piece to be punched is positioned between the punch tool and die. Typically, 15 the workpiece is clamped or mounted to an adjustable carrier mechanism, such as that described in U.S. patent no. 4,274,801, for fixing and displacing the workpiece relative to the punch tool.

The punch ram is driven, typically 20 hydraulically and under microprocessor control, to cause the punch tool to punch a hole of the desired shape in the workpiece in cooperation with the die.

The shape of the aperture punched in the workpiece will, of course, depend on the shape and

25 orientation of the punch tool (and its co-operating die).

Many applications require apertures of different shapes and configurations to be punched in the workpiece.

Accordingly, conventional punch presses which use a punch assembly having one punch tool and a mating die require

30 the changing of the punch tool and die whenever a different hole size or configuration is required.

^ There are known punch presses which employ magazines containing a number of different size punch

,/ tools and dies, enabling the punch tool and die to be

35 changed, either manually or automatically. Examples of punch presses having tool changers can be found in U.S. patents nos. 4,719,691; 4,682,401; 4,649,622; 4,486,941; 4,485,549; 4,423,546; 4,196,501; 4,103,414; 3,816,904; 3,745,646; 3,628,231 and 3,678,562.

However, such tool changers have several inherent disadvantages. First, the tool changers are normally of complex and costly construction, and therefore add to the overall cost of the punch press. Secondly, punching operations must be stopped while the tool is changed. Although automatic tool changers enable tools to be changed with relatively short idle times, it has been found that with frequent tool changes, the idle times can add up to an amount which is no longer negligible. Such idle times increase the overall process time. Thirdly, the tool changers are normally mounted adjacent the punching head assembly and may impede the movement or positioning of the workpiece, or otherwise limit the size of the workpiece.

To obviate the delay necessarily incurred when changing tools, U.S. patent no. 4,168,644 describes a punch press having a plurality of independent reciprocating punch rams each having its own tool mounted thereto. In this manner, at least one punch may continue operating while a tool is being changed on another punch. However, such punch duplication has the obvious disadvantage of increasing construction costs significantly, as well as increasing the complexity of the programme control.

To minimise tool requirements and tool changes, it is also known to rotate the punch tool while it is still mounted to the punch ram, in order to obtain cut- outs of different shape and configuration, particularly by using a single rotatable tool in a nibbling operation.

U.S. patent no. 4,674,373 describes apparatus for nibbling cut-outs by using a combination of rotation and displacement of the punch tool relative to the workpiece. In the described apparatus, the punch ram and die are simultaneously, but separately, rotated by a common servo motor using respective rack and pinion mechanisms. Although relatively complex hole configurations can be achieved by computer-controlled nibbling with a single punch tool, the apparatus of U.S. patent no. 4,674,373 is considered to have several inherent disadvantages. First, the tool and die rotation mechanisms are quite complex and expensive to construct, particularly the mechanism for rotating the punch ram. Secondly, such tool and die rotation mechanisms are not readily retrofitted to existing punches. It is necessary, according to U.S. Patent no, 4,674,373, to rotate the punch ram and many punch presses do not permit such rotation. Thirdly, any side loads imparted to the punch ram and/or die during punching are borne by the indexing gearing, couplings and servo motor which normally would not be designed to cope with such loads.

The side or rotational loads imparted to the ram and/or die during punching may adversely affect the accuracy of the tool positioning and/or damage the gearing and motor.

In order to achieve a variety of hole sizes and configurations without exchanging the tool on the punch ram, it is also known to use a punch tool having a plurality of punch pins. U.S. patents nos. 4,569,267 and 4,555,966 disclose a punch press having such a multi-tool punch tool assembly. The known punch tool assembly is mounted at the end of the ram and comprises a plurality of punch pins each movable between operative or inoperative positions. By rotating part of the punch tool assembly (independently of the punch ram), a selected punch pin can be moved from its inoperative to operative position. A cooperating die, with apertures dimensioned and configured similarly to the punch tool pins is provided.

The known multi-tool punch assembly however, does not readily permit the use of a stripper plate (which must also be rotated to align with the selected punch pin). Furthermore, to enable the known punch tool assembly to be used on a conventional punch press, considerable modification of the punch press is required to implement the selection mechanism which effects selection of the desired punch pin. For this reason, the punch tool assembly of U.S. patents nos. 4,569,267 and 4,555,966 is not suitable for retrofitting to conventional punch presses.

It is an object of the present invention to overcome or substantially ameliorate at least some of the above disadvantages by providing improved means for rotating the punch tool, and preferably the co-operating die, on a punch press.

It is a preferred object of the invention to provide a punch tool and die rotational mechanism which can be readily retrofitted to a conventional punch press. It is a further preferred object of the invention to provide a punch tool and die rotation mechanism in which the punch and die may be rotated, independently and/or interdependently, about two respective axes for the purposes of tool orientation, tool selection, tool staging and/or tool adjustment.

In some punch presses, progressive or staged forming and punching operations are performed by progressing to successive tooling, each of which performs only one of the required operations on the same portion of the workpiece. This requires changing the tool and/or die of the preceding operation with the tool and/or die for the succeeding operation either manually or by an automatic tool loader/changer. Again, tool change times often become a significant factor in the overall process times which is undesirable as the punch press is idle during changing of tools.

It is a further object of the present invention to ameliorate the disadvantages of known staged operations by providing an improved punch or die assembly for use in progressive or staged punching and/or forming operations.

In a conventional punch press, the workpiece is normally clamped, along one side thereof, to a carrier mechanism which is computer controlled to translate the workpiece along the X and Y axes and place the desired portion of the workpiece directly under the punch tool. Positioning is based on the assumption that the dimensions of the workpiece do not change appreciably.

One edge of the workpiece sheet is normally held in clamps fixed to a carrier mechanism. Typically, the edge of the workpiece sheet is received and held within the jaws of two or more clamps. When a hole is punched in a metal plate, stresses are induced in the plate, thereby resulting in the deformation of the metal around the hole. When a plurality of holes are punched in a metal plate, such as during a typical perforating operation, a substantial amount of material is removed and the combined induced stresses result in substantial bending of the metal plate.

Conventional clamps are normally fixed in position along the vertical axis. During perforating operations using fixed clamps, the deformation of the sheet, combined with the rigidity of the clamps, often results in jamming of the sheet between the clamps and the plate supports. When perforating thicker metal plate, the jamming force may be sufficient to halt movement of the plate by the carrier mechanism.

Further, linear dimensions on the sheet relative to the carrier mechanism will vary as the sheet distorts out of a single plane.

It is another object of the present invention to provide improved workpiece clamping means which compensates, at least to first order, for distortion of the workpiece sheet.

It is yet another object of the present invention to provide automatically relocatable workpiece clamps.

SUMMARY OF THE INVENTION In one broad form, the present invention provides a punch press comprising a housing having a punch ram mounted for reciprocating motion in an axial direction in the housing, and punch tool means adapted to be removably and rotatably mounted to the working end of the punch ram, characterised in that the punch press comprises rotor means fixed rotationally relative to the punch tool but movable axially relative thereto, and means for rotating the rotor means to thereby rotate the punch tool relative to the punch ram.

Typically, the punch tool means is a punch tool bit which is retained axially in the end of the punch ram but is rotatable relative thereto. The punch ram suitably includes means for selectively clamping and/or braking the punch tool against rotation. The clamping means is applied for selection operations described later, released to a "neutral" position for rotation, and retracted fully during loading and unloading.

In the preferred embodiment, the rotor means comprises inner and outer rotor members which are of tubular construction and which are mounted concentrically with each other and with the punch ram. The inner rotor member is mounted to the punch ram. It is axially keyed to the punch ram but rotatable relative thereto, and rotationally keyed to the punch tool.

A key on one of the inner and other rotor members is slidable within a longitudinal channel on the other rotor member such that the inner and outer rotor members may move relative to each other in the axial or longitudinal direction, but are constrained to rotate in unison. Thus, any rotation of the rotor members will cause rotation of the tool, but the tool (and ram) may reciprocate axially relative to the rotor members.

The means for rotating the rotor means may suitably comprise a worm gear engaged with a gear ring around the outer rotor member, the worm gear being driven by a servo motor under the computer control. Preferably, the punch press includes a stripper plate assembly comprising a stripper plate rotationally mounted to a stripper carrier. The worm gear is mounted on the stripper carrier. The outer rotor member is axially keyed to the stripper carrier but rotatable relative thereto by the worm gear. The key between the inner and outer rotor members also extends axially into a radial slot on the stripper plate so that the stripper plate is thereby rotationally keyed to the punch tool via the inner rotor member. Thus, the punch tool and stripper plate are rotated in unison, but are still relatively movable in the axial direction.

Separate means are suitably provided for rotating, braking and clamping the die of the punch press. In the preferred embodiment, the die rotation means comprises a retractable die rotor positioned below the die and selectively engageable therewith. The die rotor may similarly be driven by a worm gear under program control to rotate the die. Both the tool and die rotation mechanisms provide for infinite rotational adjustment of the punch tool/stripper plate and the die, independently and interdependently.

By controlling the independent and interdependent rotation of the tool and die about their respective axes of rotation, combined with appropriate sequencing of the associated clamps and brakes, the punch press can be used to perform varied tasks with the loaded tool such as drilling, reaming, tapping, selection, adjustment and conveying, or a combination of these tasks.

The rotation of the punch tool is normally actuated by the servo motor under microprocessor control, the servo motor being located remote from the punching head, and connected to the worm gear by some form of drive means. Any mechanism for rotating a punch tool mounted on the end of a punch ram must allow for the reciprocating action of the punch. In the device of U.S. patent no. 4,674,373, a rack and pinion mechanism is used. The pinion gear formed on the punch ram is provided with teeth of sufficient width to accommodate the reciprocating movement of the punch, and hence the pinion gear, relative to the rack. Such a mechanism involves considerable alteration to the existing punch ram and it may not be suitable for the majority of conventional punch presses. Other rigid mechanical connecting arrangements normally require highly accurate machining, and limit the positioning of the servo motor.

In the preferred embodiment, a flexible drive means is provided between the worm gear and the servo motor which is located remote from the punch tool, the flexible drive thereby accommodating the reciprocal motion of the punch tool and providing flexibility of mounting position for the servo motor.

The flexible drive may suitably be a cable, or a series of constant velocity jointed links, or the like. Typically, the flexible drive is connected between (i) a servo motor which is controlled by a microprocessor control system for the punch, and is mounted in a fixed frame of reference, such as on the punch frame or housing, and (ii) a tool or die rotation mechanism such as a worm gear which is mounted on a movable portion of the punch head or die anvil assembly.

Due to tolerances, inertia, torsional elasticity, and other distortionary effects, the output position of a flexible drive may not coincide exactly with the input position, and/or the rate of change of the position of the output of the flexible drive may vary from the rate of change of the input position. To ensure accurate orientation and precise alignment between punch tool and die, the actual positions of the punch tool and co-operating die should be precisely known and controlled.

This invention also provides an improved control strategy for ensuring accurate tool positioning using a flexible drive system.

In a further embodiment, the punch tool means is in the form of a multi-tool punch assembly comprising: a housing having a plurality of selectively engageable punch pins supported therein; a projection extending through an aperture in the housing and adapted to be received and held, in use, in the end of the punch ram of the punch, the projection and housing being rotatable relative to each other; a selector member connected to the projection, whereby rotation of the housing relative to the projection causes the selector member to selectively engage one or more of the punch pins. Typically, the punch pins are located in respective bores in a block member within the housing and are each movable axially between their engaged and disengaged positions. Each punch pin is preferably biased, by spring means or the like, to its disengaged position but this is not necessary as the pins may be moved to their disengaged positions by the punching action of the ram. When the selector member is rotated into registry with a particular punch pin, that punch pin is moved to its engaged position, ready for punching. The selector is moved simply by rotating the housing relative to the projection (to which the selector is connected). The projection is typically the locking pin or shank of the punch assembly.

The housing may be rotated relative to the projection by using the tool rotation mechanism of this invention which is suitable for retrofitting to existing punch presses. However, any other suitable means for effecting relative rotation between the housing and selector may be used. The selected punch pin may be repositioned to the original position by rotating the housing and projection together relative to the punch ram. Thus, to effect punch pin selection only, the tool rotation mechanism can perform selection via two equally opposed rotations of the housing, one with the selector clamped.

Alternatively, a cooperating die is suitably rotated to a similar degree as the punch assembly to maintain registry between the selected punch pin and the operative portion of the cooperating die. This is a time saving feature as the punch assembly and co-operating die do not need to be returned to a predetermined position. Preferably, the multi-tool punch assembly also includes a stripper mechanism, such as a plate, for facilitating the stripping of the punched sheet from the punch pin. The stripper plate is suitably mounted for axial movement relative to the punch pin. In another embodiment, the present invention provides an assembly comprising a body shaped to be suitable for loading and clamping to conventional punch presses; a transfer or conveying plate member that transfers material from preceding operations to succeeding operations via a rotary motion performed by such conventional presses or by auxiliary means; and a retaining plate member which both retains the transfer or conveying plate member and provides an aperture for punching and other operations. The assembly therefore not only functions as a punch or die, but also as a transfer mechanism for the material upon which progressive or staged operations are performed.

Traditionally all punch press tooling has had fixed geometry. The present invention provides a punch press mechanism for implementing continuous adjustment of a punch, stripper or die assembly. The sequenced application of clamps in conjunction with the previously described rotation mechanism of the punch press can be used to implement aperture size and profile adjustments of a tool, where these adjustments are mechanically coupled to the rotation mechanism of the punch press. Typically such adjustments may occur through threaded internal mechanisms keyed into the drive dogs of the rotation mechanism of the punch press.

Rotary motion of the punch press rotation mechanism with tool clamps applied can then perform adjustment of the tool as the tool adjustment mechanism is wound relative to the body of the tool assembly. With tool clamps released, rotary motion of the punch press rotation mechanism can perform physical reorientation of the tool through (say) friction locking of the internal adjustment mechanism to the tool body. The previously described punch press rotation and clamping mechanism is applicable to any sequence of staged or continuous motions implementing adjustment and can be combined with microprocessor control to implement programmable adjustments catering for sheet type and thickness.

According to another aspect of the invention, there is provided clamping means for holding a workpiece in a punch press or the like, the clamping means comprising a first portion adapted to be mounted to a carrier mechanism for moving the workpiece; a second portion connected to the first portion and having means for clamping an edge of the workpiece, the second portion being pivotally coupled to the first portion such that the second portion is able to make a complementary movement to distortionary movement of the workpiece due to punching or other working thereof.

In the preferred embodiment, the first and second portions are connected by at least one link member which is pivotally coupled to both. The pivotal connection between the first and second portions, as well as their geometry, enables the second portion to rise vertically relative to the first portion and also to tilt about its pivot axis. In this manner, the sheet clamping jaws on the second portion can follow the distortionary movement of the edge of a sheet which is being punch perforated, and the clamping means compensates or self- corrects, to at least first order, registration errors caused by sheet curvature.

In yet another form, this invention provides selectable clamping means, and a method of accurately relocating the clamping means under computer control.

In order that the invention may be more fully understood and put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagrammatical fragmentary cross sectional elevation of the punching head assembly of a punch press illustrating one embodiment of the invention; Fig. 2 is a fragmentary sectional plan view of the rotation mechanism of Fig. 1;

Fig. 3 is a schematic diagram of a flexible drive for use with the embodiment of Fig. 1;

Fig. 4 is a fragmentary cross sectional elevation of a multi-tool punch tool assembly according to another embodiment of the invention;

Fig. 5 is a fragmentary sectional plan of a band brake for use with the punch tool assembly of Fig. 4; Fig. 6 is a side elevational view of a workpiece clamp according to another embodiment of the invention;

Fig. 7 is a sectional elevation of a die suitable for use with multi stage forming operations, Fig. 8 is a sectional elevation of a die suitable for use with the turret tool of Fig. 4,

Fig. 9 is a partially sectional view of a relocatable clamp.

Fig. 10 is a schematic hydraulic circuit diagram for the clamp of Fig. 9, and

Fig. 11 is a model velocity chart. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiment of the invention illustrated in Fig. 1 comprises a punching head assembly with means for rotating the punch tool and its associated die, separately or together, to provide infinitely variable adjustment thereof, without requiring any rotation of the punch ram. This mechanism can readily be retrofitted to existing presses since it is not necessary to alter the existing punch ram and the main punch hydraulics significantly.

As shown in Fig. 1, the punching head assembly of a punch press comprises a punch ram 10 adapted to reciprocate within a bore formed in the punch housing 11. A punch tool 12 is detachably fitted to the bottom, or working end, of the ram 10. The punch tool 12 typically comprises a tool bit 14 of the desired size and shape fixed to a punch adaptor plate 13. A stem or locking pin 15 mounted on top of the adaptor 13 is rotatably received with a ram bore 16 formed in the working end of punch ram 10. The tool locking pin 15 can be clamped, both axially and rotationally, within the bore 16 by a tool clamp assembly 17 comprising an hydraulically operated wedge. The tool clamp assembly 17 is under programme control, and can be actuated (engaged) automatically to clamp the punch tool 12 in the working end of ram 10, or retracted (released) to allow the punch tool 12 to be removed and replaced through a radial cutaway loading passage formed in the side of ram 10, as can be seen in Fig. 1. The tool clamp assembly 17 can be moved to a "neutral" position, represented by the dotted outline, during rotation of the punch tool 12.

A stripper assembly is also provided on the punch press. The stripper assembly comprises a stripper plate 20 mounted to a tubular stripper carrier 21 which is able to be reciprocated axially relative to the punch housing 11 by hydraulic cylinder 22. That is, the stripper carrier 21 is fixed to the stripping piston of hydraulic cylinder 22. One or more stripper stops or retainers 23 locate the stripper plate 20 in the correct position when inserted laterally. The operation of the stripper assembly and the punch ram are independently controlled by the punch press control system, which is microprocessor-based.

A retractable clamp 37 is mounted to the stripper carrier 21 for clamping the stripper plate 20 against rotational movement. Thus, any side load, torsional or other rotational force applied to the stripper plate 20 during punching will be borne by the clamp 37 and the stripper stop(s) 23, rather than the worm gear 30 (described below).

The mechanism for rotating the punch tool 12 comprises a first rotor member in the form of a rotor sleeve 25 mounted concentrically with ram 10 and keyed axially to the ram 10, but rotatable relatively thereto about its axis. In other words, the rotor sleeve 25 is mounted on, and fixed axially to, the ram, but is able to rotate around ram 10. The rotor sleeve 25 is rotationally keyed to the tool adaptor plate 13 by a key 26 so that the rotor sleeve 25 and punch tool 12 are constrained to rotate in unison.

The tool rotor sleeve 25 is also rotationally keyed to a second rotor member in the form of a stripper rotor sleeve 27 by a vertical key 28. The stripper rotor sleeve 27 is mounted concentrically with the tool rotor sleeve 25, on the outside thereof. The key 28 is fixed to the stripper rotor sleeve 27, but longitudinally slidable within a vertical channel formed in the tool rotor sleeve 25. The bottom end of key 28 locates within a keyway in the stripper plate 20. In this manner, the punch tool 12 and the stripper plate 20 are constrained to rotate in unison, but the stripper plate 20 may be moved axially by hydraulic cylinder 22 relative to the punch tool 12.

As shown in Fig. 1, the stripper rotor sleeve 27 is mounted concentrically within, and radially adjacent to, the tubular stripper carrier 21. The stripper rotor sleeve 27 is rotatable within the stripper carrier 21, but is keyed to the stripper carrier 21 to prevent any relative axial movement. A gear ring 29 is formed, or mounted, around the outer circumferential surface of the stripper rotor sleeve 27 for engagement with a worm gear 30 journalled transversely in stripper carrier 21, as shown in more detail in Fig. 2. (The punch tool 12 and other detail are omitted from Fig. 2 for clarity. ) The worm drive is designed so as not to be self-locking.

The worm gear 30 is mounted on a shaft 36 on which is also mounted a rotary position measuring device, such as a rotary encoder 31. In this manner, the output of the rotary encoder 31 will provide direct and accurate indication of the rotary position of worm gear 30 and hence the angular position of the punch tool/stripper plate assembly. » Punch tool rotation systems in which the tool is coupled to a servo motor by rigid elements generally require surfaces and components to be machined to high accuracy. Furthermore, the use of such rigid interconnecting elements between the tool and the servo motor generally limit the mounting position of the motor and the nature of movement(s) between the motor and the tool.

In the illustrated embodiment, one end of shaft 36 is connected to a first end of a flexible drive 35, via a coupling 32. The other end of flexible drive 35 is connected to the shaft of a servo motor 34 via a coupling 33, as shown schematically in Fig. 3. The servo motor 34 is controlled by the punch press control system to rotate both the punch tool 12 and the stripper plate 20 relative to the punch ram 10, via the flexible drive 35 and the worm gear 30. Typically, the servo motor 34 is mounted to the punch frame or housing in a suitable, fixed position. The flexible drive 35 is a simple and economic means of permitting the worm gear 30, and the punch tool/stripper plate rotation mechanism which it drives, to reciprocate vertically while the servo motor 34 remains fixed to the punch housing.

The use of a flexible drive shaft to couple the servo motor to the worm gear avoids the need for highly accurate machined surfaces and components, and allows greater flexibility in the positioning of the servo motor.

Typically, rotary position measuring devices are mounted at the rear of the servo drive motors, on the shaft thereof. The accuracy of the drive system is therefore subject to errors caused by backlash, pitch errors, etc. in the linkages connecting the servo motor to the tool. In the present invention, the rotary encoder 31 is mounted on the same shaft as the worm gear

30, and thereby provides a direct position measuring system, with the output of the rotary encoder 31 indicating the precise position of the worm gear 30, and hence the punch tool/stripper plate assembly.

An improved control strategy is used for the flexible drive to provide for accurate control of the tool position. All control strategies for positioning a mechanical system have a model which the designer expects the physical system to closely follow. Let the model position as a function of time for a move be X(t) and the actual position for that same move be x(t). As a result of system time constants, x(t) ≠ X(t). If the position error e(t) is defined by e(t) = x(t) - X(t) ...1 then -e(t) is commonly referred to as the position lag.

The aim of control strategies is to ensure -that the position error remains small and is suitably damped so as to minimise the settling time at the end of a move.

A conventional control system usually consists of a supervisory central processing unit commanding an amplifier to power the motivator (for example a motor) for the system. This motivator feeds back into the central processing unit position information and other (if appropriate) time derivatives of position. The only necessary requirement is that the position loop be closed, i.e. that position be fed back. The central processing unit or additional specialised hardware can provide any position time derivatives. A simple and very common control strategy used in industry has a command output 0_o to the amplifier consisting of the model velocity supplemented by a stabilising correction proportional to the position lag. Then the further the system lags the model, the larger is the restoring command supplied to correct the situation.

Thus

0_c = bX + c (X - x) ...2

This is a velocity output command. In such a control strategy the velocity is usually fed back from the drive motor tachometer and subtracted from the output command 0_c at the input stage to the . amplifier. This provides a current command which is amplified to power the drive motor. For a non-torsioning drive, this motor current is proportional to motor torque and hence axis acceleration.

Thus

0 - βx = αx ...3

Where α is the effective inertia of the system.

In the above equation, β, b and c are constants defining the proportions of actual velocity, model velocity and position lag which figure in the control strategy αx + βx - bX + c(x - X) = 0 ...4 obtained by substituting equation 2 into 3. This can be re-arranged to give αe + βe + ce = αX + (b - β)X ...5 which describes a damped harmonic oscillator for the position error with forcing function dependent on the model acceleration and velocity. This oscillator can be chosen to be critically damped for the given system inertia by a suitable choice of the feedback proportion β for the oscillator natural angular frequency c. Larger system dampening occurs as β is increased but there are usually practical limitations associated with the tachometer ripple which limit the size of β and hence the position loop gain. Further, the form of the forcing function of the right hand side of equation 5 can be chosen for piecewise linear models X(t) to exercise only the least dominant harmonic mode. This is achieved by having a root of the numerator of the transfer function coinciding with a root of the denominator.

This describes a standard and common place control strategy. The strategy however, does not cater for zero position error when holding position in a practical application, as there is always a level of static friction F_ which balances the position error e through the term ce in the control strategy 5. For the dynamic motion 5, F_s is insignificant, but must be included in 3 on the right hand side during settling.

This invention overcomes the problem by including time dependence in the position error correction of 2. This is best achieved by the time integral of position error. The described known strategy also does not cater for torsions of the drive shaft which gives rise to an extra term γx on the right hand side of 3. The constant γ is related to the elastic torsion constant of the shaft. The inclusion of the fourth order time derivative inherently changes the character of the control strategy as two more modes of oscillation are now available arising from the torsion of the shaft.

To control these in a damped manner, feedback proportional to x is included. Finally, for piecewise linear models X(t), inclusion of all derivatives with non-zero support (i.e. up to and including X) caters for amplifying systems with significant time constants. Servo valves and proportional valves are typical examples.

According to the present invention, the control strategy for a flexible drive requiring zero position error when holding position therefore has an output command.

0 = aX + bX + c(X - x) + d \(X - x) dt' ..6

where the amplifying stage gives K-

0_e - βx - η^'x - αx + γx^" Thus

-γx^' - ηx + (a - α) X + (b - β) X

If we let E(tt)) ee((tt])dt be the time integrated position error

then

V^'E^" + η__^' + α^*E + β^'έ + cE + dE =

-γx^" - ηX + (a - α)X + (b - β)X ...7

where of the constants of proportionally, γ and α are related to the flexible shaft torsion period squared and system inertia, respectively, which are properties of the mechanical system, η and β are the introduced electronic dampening mechanism for the torsional and linear oscillations and are determined by practical hardware limitations, and a, b, c, d are somewhat user definable. Of these remaining four constants, we can quite arbitrarily take b ≡ 1 to define the units of 7 and then the constant a is the amplifying system's inbuilt inherent time constant. The constants c and d, which are the position error and position error time integral gain constants, can then be chosen to provide a degree of critical dampening and mode elimination to minimise the settling time at the end of a move. In the preferred embodiment, the control strategy is implemented by suitable software within the central processing unit by having an interrupt requested every 3.41 milliseconds (say). The code which is run by this interrupt first reads from the position feedback counter the current position x. The model position at this point in time during the move is known from the piecewise linear model velocity of Fig. 11, where after n loops of 3.41 milliseconds through such a move, the model acceleration, velocity and position are all known. In 6 then the central processing unit can calculate aX + bX + c(X - x) The current time integrated position error is calculated every loop by adding the current loop's position error multiplied by the loop period 3.41 milliseconds to the previous value of the time integrated position error. That is,

n-l x)dt + (X - x)(t_n - t_n._x)

< -_- for small time increments (on the scale of the system time constants). Thus the output command equation 6 can be calculated and output to the drive amplifier for accurate control of the system.

Referring to Fig. 1, the punching head assembly includes a die 40 having a die aperture 41 therethrough which is shaped and dimensioned to suit the tool bit 14. It will be apparent to those skilled in the art, that any rotation of the punch tool 12 will normally require a corresponding rotation of its co-operating die 40 in order to maintain a registry between the tool bit 14 and die aperture 41. The present invention provides a mechanism for rotating the die 40, and an embodiment of this mechanism is also illustrated in Fig. 1.

The die rotation mechanism comprises a generally tubular die rotor 42 having a plurality of upstanding pins 43 projecting from its top end. The pins

43 are received in respective mating recesses or sockets

44 located in the bottom of die 40.

The die rotor 42 is located concentrically with the axis of the punch ram 10, punch tool 12, stripper plate 20 and die 40. As can be seen in Fig. 1, an outwardly directed flange portion at the bottom end of the die rotor 42 is journalled within a formation in die gear housing 45. That is, the die rotor 42 is rotatable about the punch axis, but is fixed axially relative to the housing 45. The housing 45, in turn, is connected to a post 46 fixed to the punch frame 47, via a telescoping slide joint 48 and a ball joint 49. The housing 45 is supported by a spring support 50 which biases the housing

45 upwardly. However, the housing 45 may be depressed by a hydraulic cylinder 51 mounted in the punch frame 47 above the housing 45.

The hydraulic cylinder 51 is actuated, by the punch press control system, to depress the gear housing 45 against spring 50 to thereby lower die rotor 42 and retract the pins 43 from their respective sockets 44 in the bottom of die 40. This enables die 40 to be removed laterally. The telescope joint 48 and the ball joint 49 provide the necessary degrees of freedom to enable the rotor 42 and housing 45 to be depressed relative to the post 46 and punch frame 47.

The die rotation mechanism further comprises a gear ring 52 formed on the outer peripheral face of the flanged bottom portion of die rotor 42. The gear ring 52 engages a worm gear 53 journalled in gear housing 45. The worm gear 53 is provided with a rotary encoder (not shown) and is driven from a servo motor via a flexible drive in a similar manner to the worm gear 30 described above with reference to Figs. 1 to 3. The servo motor for rotating worm gear 53 is also controlled by the punch control system.

Rotation of worm gear 53 results in rotation of the die rotor 42 within its bore in the punch frame 47. Due to the engagement of the projecting pins 43 in their respective sockets 44, the die 40 will be constrained to rotate with the die rotor 42. In this manner, the die 40 can be rotated to the same degree as the punch tool 12, both under the control of the punch press control system.

One or more die stops or retainers 54 locate the die 40 in the correct position when it is inserted laterally. A retractable clamp 55 clamps and fixes the die 40 in position against the die retainer(s) 54. When the die 40 is to be removed laterally, the clamp piston 55 is retracted below the level of the die base.

The punch control system typically comprises a microprocessor or other programmable computer device having inputs connected to sensors or switches on the punch press, and outputs connected to hydraulic cylinders or other actuating devices.

Operation of the rotating mechanism of the preferred embodiment will now be described with reference to Figs. 1-3. Prior to the loading of the punch tool 12, stripper plate 20 and die 40, the clamp pistons 37, 55, the tool clamp assembly 17 and the die rotor 42 and its associated pins 43 are all retracted to clear the loading passage for the punch tool, stripper plate and die. The rotors are returned to the zero position with alignment keys parallel to the passage of entry. The punch tool 12, stripper plate 20 and associated die 40 are side loaded into the punching head assembly, either manually or by an automatic tool loader/changer. Die 40 locates against the die stop(s) or retainer(s) 54. Stripper plate 20 locates against stripper stops or retainers 23. When the punch tool 12 is side loaded into the punch ram, key 26 on rotor 25 locates within a recess in the periphery of the tool adaptor plate 13. The tool locking pin 15 locates within ram bore 16 and is clamped in that position by the clamping assembly 17. In this manner, the punch tool 12 is fixed axially by the punch clamp assembly 17, and rotationally by key 26 and also by clamp 17. Retractable clamp piston 37 is extended to clamp stripper plate 20 against retainer(s) 23 prohibiting rotation of the stripper plate and providing concentric alignment with the tool. Since the punch tool 12 and stripper plate 20 are rotationally locked together by keys 26, 28, the tool is also prevented from rotation.

Retractable clamp piston 55 is extended to clamp die 40 against the retainer(s) 54. Hydraulic cylinder 51 is also retracted, thereby permitting rotor 42 to rise and locate its pins 43 in their respective sockets 44 in the bottom of die 40. A workpiece, typically a metal sheet or plate 56 is located between the punch tool 12 and die 40, typically by a carrier mechanism controlled by the punch press control system. In use, the stripper plate 20 may be depressed against the workpiece 56 by the stripper cylinder 22 momentarily before the tool bit 14 punches the sheet 56. The stripper plate 20 is retained against the sheet 56 until after the punch tool bit 14 has been retracted therefrom, to thereby ensure that the sheet 56 is stripped from the punch tool. Other punching methods, such as those described in U.S. patent no. 4,823,658, may be achieved using the independently operable punch and stripper drive cylinders. After punching, the workpiece 56 is repositioned by the carrier mechanism so that the next portion of the sheet 56 to be punched is located between the punch tool bit 14 and die aperture 41.

If rotation of the punch tool 12 is required, for example in nibbling operations, both the retractable stripper clamp piston 37 and the punch clamping assembly 17 are first retracted slightly to a "neutral" position. In this position, the punch tool clamping mechanism and the stripper plate clamping mechanism restrain the punch tool and stripper plate, respectively, both axially and traversely, but do not exert any significant anti- rotational force on the punch tool or stripper plate. The worm gear 30 is then rotated to the desired degree by servo motor 34 via the flexible drive 35, thereby rotating the punch tool 12 and stripper plate 20 to the required angular position. Similarly, when rotating the die 40, the clamp piston 55 is first retracted slightly to a "neutral" position, shown in broken outline, and the worm gear 53 is rotated by its respective servo motor so as to rotate the die rotor 42 and the pins 43 at the top end thereof. As the pins 43 engage in corresponding sockets 44 in the die 40, the die 40 will rotate with the die rotor 42.

After the punch tool 12, stripper plate 20, and die 40 have been rotated to the desired orientation, clamps 37, 17 and 55 are re-engaged and the punching operation may continue.

If the punch tool 12, stripper plate 20 and die 40 are to be removed, the workpiece 56 is first moved away from the punching head assembly. The rotors are then rotated to their zero position. Clamps 37, 17 and 55 are fully retracted to the positions shown in broken outline, and hydraulic cylinder 51 is extended to cause pins 43 to be retracted from their respective recesses 44. The punch tool 12, stripper plate 20 and die 40 can then be removed and/or exchanged, either manually or by an automatic tool changer.

It will be apparent to those skilled in the art that the above described punch tool, stripper plate and die rotation mechanisms have several advantages over known tool rotation systems. First, only the toolset (i.e. punch tool, stripper plate and die) is rotated, and no rotation of the punch ram is required. Secondly, the toolset elements (i.e. punch tool, stripper plate and die) are clamped against non-rotating datum ensuring greater precision. Thirdly, the rotating mechanisms can be retrofitted to an existing punch press without major modification. Fourthly, the stripper assembly can reciprocate independently of the tool, yet both are rotated simultaneously and are infinitely adjustable in angular position. Fifthly, the flexible drive systems allow greater flexibility in the positioning of the servo motors. Sixthly, the punch tool and die may be rotated independently and interdependently with each other and can be employed to perform tasks involving rotary motion such as drilling, reaming, tapping, etc. Finally, any side loads or torsional forces on the punch tool, stripper plate and/or die are borne by clamps rather than the respective worm gears 30 and/or 53.

In a further embodiment, the present invention provides a multi-tool punch tool assembly, or "turret tool", an example of which is illustrated in Fig. 4. The turret tool comprises a tool shank or locking pin 60 having a selector arm 61 fixed transversely to the bottom thereof as shown in Fig. 4. The selector arm 61 has a bevelled edge 62 at a predetermined radial portion thereof for reasons which will become apparent from the following description. The top end of the tool locking pin 60 extends through an aperture in a bell-shaped housing 63 which has a slot or keyway 64 at its top peripheral edge which locates with a key 26 on the rotor sleeve 25. The housing 63 includes an internal block member 65 having a plurality of bores therethrough in which are located respective punch pins 66 (66A, 66B, ..). Each punch pin 66 is movable axially within its respective bore between an elevated (inoperative) position and a depressed (operative) position. Preferably, the punch pin(s) 66 are biased upwardly in their respective bores to their inoperative positions by springs or other suitable means, but this is not a necessary requirement.

The bottom edge of housing 63 is shaped to captively retain therein a stripper plate 67, yet permit axial movement of the stripper plate 67 relative to the housing 63. Preferably, the stripper plate 67 is spring-loaded and biased downwardly relative to the housing 63 by springs 68. The stripper plate 67 is provided with apertures 69 corresponding in size, shape and location to the punch pins 66 to permit the punch pins 66 to pass through their respective apertures 69 in the stripper plate during punching operations.

In use, the turret tool of Fig. 4 is inserted into a punch press of the type illustrated in Fig. 1, the locking pin 60 being received in ram bore 16, and keyway 64 being located in tool rotor 25, via key 26. When the selector arm 61 is located over a punch pin 66, that punch pin will be depressed to its operative position, i.e. that punch pin will be selected for punching operations. The selector mechanism may be detented to align automatically with a selected punch pin. Typically, the selector arm 61 is sized and shaped so that only one punch pin 66 is selected at any one time. However, if desired, the selector arm 61 may be sized and shaped so as to simultaneously place two or more punch pins into their operative positions. Preferably, when the turret tool of Fig. 4 is used in a punch press, a brake is employed around the tool rotor 25. In the illustrated embodiment, a band brake mechanism is used. In the band brake, illustrated in Fig. 5, hydraulically operated pistons 70 retract the inner band 71 of the band brake, causing the brake band 71 to seize and rotationally clamp the tool rotor 25, and hence the turret tool housing 63, since the two are keyed together by key 26 and keyway 64.

If a particular punch pin 66 is to be selected for punching operations, the band brake 71 is first released, but the tool clamping assembly 17 remains engaged to hold tool pin 60 stationary. Worm drive 30 is then rotated, via its flexible drive 35, by its servo motor 34 under software control from the punch press control system. The rotation of the worm gear 30 causes the rotor 27 to rotate. Since the tool rotor 25 is keyed to the outer rotor 27, and as the housing 63 is also keyed to the tool rotor 25 via key 26, the housing 63 will rotate about tool pin 60. As the pins 66 held within their respective bores in block 65 pass under the selector arm 62, they will be individually depressed to their operative position, the bevel formed on the edge of selector arm 61 facilitating the depression of the individual punch pins 66. The housing 63 is rotated by worm gear 30 until the desired punch pin 66 is located under selector arm 61, and hence depressed into its operative position.

A cooperating die 100 (illustrated in Fig. 8) with body 101 and a plurality of inserts 102, 103 is similarly rotated by worm gear 53 (as described above) so that the selected punch pin is aligned with its cooperating bore in the die. The band brake 71 and die clamp 55 are then reapplied to clamp the die 100 and turret tool body 63. The punching operations can then proceed with any side loads or torsional forces on the punch tool, stripper plate and/or die being borne by these clamps rather than the respective worm gears 30 and/or 53. The control system takes into account the fact that the selected punch pin may now be displaced from the previously selected punch pin.

Alternatively, if it is desired to move the selected punch pin to the same operating position as the previously selected punch pin, the tool clamping assembly 17 is retracted slightly to a "neutral" position, the band brake 71 is released, and worm gear 30 is turned so as to rotate housing 63. Due to a slight degree of static friction between the housing 63 and tool pin 60, the tool pin 60 will rotate with the housing 63 so that the selector arm 61 keeps the selected punch pin in the operative position. Once the selected punch pin is moved to the desired operating location, the band brake 71 and the tool clamping assembly 17 are re-engaged to allow punching to proceed. If a particular die is to be selected in co¬ operation with a punch pin, the die clamp 55 is released to a "neutral" position as shown by the dotted outline in Fig. 1. Worm drive 53 is then rotated via a similar flexible drive and servo motor to that described earlier under microprocessor control. The rotation of the worm gear causes the tubular die rotor 42 to rotate. Since the die 40 is engaged to the die rotor keys 43 at the top of the die rotor 42 via sockets 44 the die will rotate about its axis. The die is rotated under microprocessor control to the precise position at which the new co-operating die aperture is aligned with the axis of the selected punch pin(s).

In the case where a fixed position is required, such as when a new co-operating die aperture is chosen, the die clamp 55 is re-engaged clamping the die at the completion of the rotation.

If the required movement is for drilling, tapping, reaming, adjusting via rotary cams etc., then the die can be rotated to successfully perform that function.

Further, the turret tool invention allows the selection of different dies independently of punch tool selection. This has the advantage of selecting co- operating dies of different die aperture size with a given punch pin thereby altering the punch pin/die aperture clearance. This is significant when performing punching operations on varying material thicknesses as the required die clearance is directly proportional to material thickness.

Further the rotation mechanism of this invention may also be used for general rotary motion and selection operation such as drilling, reaming, tapping, adjusting via rotary cams selection, conveying etc.

The turret tool illustrated in Fig. 4, in association with a cooperating die, is particularly suitable for use in multi-stage forming or multi-step punching operations. The use of the turret tool in such operation will now be described by way of example, with reference to the punching of washers from metal sheet.

In this example, a turret tool having at least two punch pins is used, one punch pin corresponding to the outer diameter of the washer to be produced, while the other punch pin corresponds to the inner diameter. A cooperating die having corresponding bores is also used.

In the first punching step, the inner diameter punch pin punches out a slug to leave a hole in the metal sheet which will form the washer bore. The turret tool is then rotated to select the outer diameter punch pin and position it concentrically with the hole. The die is rotated accordingly. The outer diameter punch pin then punches out the washer.

It will be apparent to those skilled in the art that the turret tool, in combination with a cooperating die, has many applications in multi-stage punching and forming operations. The present invention also provides an improved die assembly capable of staging material through a progression of operations, an example of which is shown in Fig. 7. The multi-staged or progressive die assembly 90 comprises a die body 91 shaped in the outer profile to be loaded and clamped with conventional punch presses. A transfer or conveying plate 92 is retained axially by the die body 91 and a retainer/die plate 93, but is free to rotate relative to die body 91 and retainer/die plate 93. The transfer plate 92 conveys material through each successive staged operation. In the illustrated embodiment, the die assembly comprises at least two apertures 94 and 95 for punching operations.

Movement of the transfer or conveying plate 92 can be achieved manually or automatically by rotation of an indexing/rotation mechanism described earlier with reference to Fig. 1, or the like, or by auxiliary motor arrangements controlled by mechanical means or microprocessor control.

The use of the multi-staged or progressive tool for multi-stage forming or multi-stage punching operations will now be described by way of example, with reference to the punching of washers from metal sheet and

Fig. 7.

In this example, in conjunction with a co¬ operating punch a staged die having at least two apertures 94 and 95 is used, one (94) corresponding to the outer diameter, while the other die aperture (95) corresponds to the inner diameter.

In the first operation, a blank having an outer diameter of the washer is punched out of the metal sheet through aperture 94. The transfer plate 92 is rotated so the blank is positioned over the aperture 95 corresponding to the inner diameter and the blank is punched, producing the finished washer.

A further rotation of the transfer plate passes the completed washer over an exit hole thereby removing the washer from the die assembly 90, while loading another blank over the second aperture 95. By punching the outside diameter before punching the inside diameter, punch distortion of the washer is minimised.

It will be apparent to those skilled in the art that the multi-staged die, used in combination with a co¬ operating punch, also has many applications in multi¬ stage punching and forming operations. The present invention also provides an improved work clamp with a degree of freedom of movement in the vertical axis to compensate or allow for such distortion of the plate. Further, the clamp compensates for the induced angularity of the end of the plate as well as for the change of length of the plate along the horizontal axis.

As shown in Fig. 6, a pivotable work clamp comprises a rear body portion 72 mounted on a horizontal beam 73 which is adjustable in position under the control of the punch press control system.

The pivotable clamp also includes a front body section 75 having a clamp mouth 80 adapted to receive the workpiece plate therein and to be clamped between its jaws. The front body section 75 is connected to the rear body section 72 by a pair of plates 76 on opposite sides thereof, each plate 76 being pivotally connected at 77, 78 to the front and rear body sections 75, 72, respectively. In this manner, the front body section containing the clamp mouth 80 not only is movable in the vertical direction relative to the rear body section 72, but also is pivotable about the horizontal axis. The allowable movement of the front body section 75 relative to the rear body section 72 is defined by the relative spacing and positioning of the pivot axes 77, 78, the geometry of the front body section 75 and the profile of the opposing faces of the front and rear body sections.

Such spacing, positioning, geometry and profiles are selected and designed so that, in use, as the clamp mouth 80 rises and turns due to deformation of the metal plate being punched, there are two opposed and equal offsets. The front body section 75 moves upwardly, but also pivots about pivot axis 77 to compensate for the angular deviation of the edge of the metal plate. In other words, the front body section 75 moves such that the clamp mouth 80 performs a complementary movement to that of the edge of the steel plate. This complementary movement compensates for registration errors induced by sheet curvature, ie. variations in the linear dimensions of the metal plate in the horizontal plane due to the curvature of the plate. A locking pin 79 may be inserted through the connecting plate(s) 76 and into a composite bore formed between the opposing faces of the front and rear body sections, thereby fixing the front body section 75 relative to the rear body section 72 and converting the clamp assembly to a conventional rigid clamp.

The workpiece clamps are normally mounted on an elongate member which serves as a positioning axis. Typically, two or more clamps are mounted at spaced locations on the positioning axis to hold an edge of a workpiece sheet. The immediate region of each clamp is a "dead zone" in which no punching or other operations may be performed. It is therefore necessary to shift the clamps if the workpiece sheet is to be punched or worked within that dead zone. There are known mechanisms which retract the clamps, but such mechanisms usually waste throat depth of the machine tools and are relatively large and bulky. Further, such retraction mechanisms do not allow for automated location/relocation of the individual clamps and therefore must be manually located. This invention provides a method and apparatus for automated or computer-controlled repositioning of workpiece clamps, and an embodiment thereof is illustrated in Figs. 9 and 10. The invention does not require any additional coordinate axis to perform the automated location of individual clamps. Use is made of the existing coordinate axis.

As shown in Fig. 9, a clamp 80 comprises two clamp body members 81, 82 which are brought together by clamp cylinder 83 to clamp the clamp at a fixed longitudinal position on rail 84 of positioning beam 85.

A material clamping cylinder 86 is provided to enable the jaws 87 of the clamp 80 to clamp the workpiece therebetween.

The clamp 80 also includes a spool valve 88 which is mechanically actuated by piston rod 89. Upon depression of the end of the piston rod within its associated recess on the underside of clamp 80, the spool valve 88 releases clamp cylinder 83 and workpiece clamping cylinder 86. A projection, such as a shotpin 90, is mounted on the punch frame below the line of travel of the piston rod 89. The shotpin 90 is mounted on the piston rod of a cylinder 91 which enables the shotpin 90 to be elevated and retracted under the control of the punch computer control system.

A suitable hydraulic circuit for the clamp 80 is illustrated in Fig. 10. Normally, the workpiece clamping cylinder 86 is actuated to clamp the workpiece between jaws 87, and the clamp cylinder 83 is actuated to fix the clamp 80 to the rail 84. Typically, two or more clamps are used to mount the workpiece to the beam 85. The workpiece can be translated in position by moving the positioning axis beam 85 to place the desired portion of the workpiece sheet in alignment with the operative tool. The beam 85 itself may be translated along an orthogonal axis to thereby provide positioning on both the X and Y axes.

To relocate a clamp 80, the shotpin 90 is elevated by its associated cylinder 91, after the beam 85 is moved to locate recess 93 over shotpin 90. Up to this stage, both the workpiece clamping cylinder 86 and the clamp cylinder 83 of each clamp are clamped "ON" by a solenoid valve 94 controlling all the cylinders. However, when shotpin 90 is received within recess 90, piston rod 89 is displaced upwardly to actuate spool valve 88 which, in turn, releases the workpiece clamping cylinder 86 and the clamp cylinder 83 for that particular clamp. The beam 85 (and the workpiece) are then able to be moved relative to the released clamp 80 under computer control. The beam 85 is shifted to relocate clamp 80 along the beam. With the clamp in the new desired position, shotpin 90 is retraced by cylinder 91 which releases the spool valve 88, and clamps workpiece clamping cylinder 86 and clamp cylinder 83 back "ON".

The above described arrangement permits clamps to be automatically relocated along the positioning axis with a high degree of accuracy and under computer control. The positions of the clamps are stored in memory and the relocation procedure can be incorporated in any software control programme where necessary.

It is to be noted that only the clamp to be relocated is released, and the operation of the remaining clamps is unchanged. The relocatable clamps can be readily retrofitted to existing axes.

The foregoing describes only some embodiments of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the following claims.

Claims

CLAIMS :

1. A punch press comprising a housing having a punch ram mounted thereon for reciprocating motion in an axial direction, and punch tool means adapted to be removably and rotatably mounted to the working end of the punch ram, characterised in that the punch press comprises rotor means fixed rotationally relative to the punch tool means but movable axially relative thereto, and means for rotating the rotor means to thereby rotate the punch tool means relative to the punch ram.

2. A punch press as claimed in claim 1, wherein the rotor means comprises inner and outer tubular rotor members mounted concentrically with each other and with the punch ram, the inner rotor member being rotationally keyed to the punch tool means and the outer rotor member, but being movable axially relative to the outer rotor member.

3. A punch press as claimed in claim 2 wherein the outer rotor member has a gear ring on the outside thereof, further comprising a worm gear operatively engaged with the gear ring and a servo motor connected to the worm gear, whereby in use the outer rotor member is rotated by the servo motor.

4. A punch press as claimed in claim 3 wherein the servo motor is located remotely from the worm gear and is connected thereto by flexible drive means.

5. A punch press as claimed in claim 4 wherein the servo motor is controlled by a computer-based control circuit having an input connected to a position sensor mounted to the worm gear, the servo motor being controlled according to a predetermined control strategy.

6. A punch press as claimed in claim 1 wherein the punch press comprises clamp means for selectively clamping the punch tool means against rotation relative to the punch ram.

7. A punch press as claimed in claim 3 further comprising a stripper plate assembly having a stripper plate with an aperture therein through which the punch tool means is adapted to pass, the stripper plate being mounted to a tubular carrier member surrounding the punch ram, and a hydraulic cylinder mounted between the carrier member and the housing, whereby the stripper plate is reciprocally movable in the axial direction relative to the housing independently of the punch ram..

8. A punch press as claimed in claim 7, herein the stripper plate is rotationally keyed to the inner and/or outer rotor members, but movable axially relative thereto.

9. A punch press as claimed in claim 1 further comprising a die member operatively associated with the punch tool means and removably mounted on the housing below the punch ram, and die rotation means for rotating the die member on the housing, the die rotation means comprising a retractable die rotor located below the die member and selectively engageable therewith, and means for rotating the die rotor.

10. A punch press as claimed in claim 9 wherein the die rotor has a gear ring thereon and the means for rotating the die rotor comprises a worm gear engaged with the gear ring, and a servo motor connected to the worm gear by flexible drive means.

11. A punch press as claimed in claim 1, wherein the punch tool means is a multi-tool punch assembly comprising: a housing having a plurality of selectively engageable punch pins supported therein; a projection extending through an aperture in the housing and adapted to be received and held, in use, in the working end of the punch ram, the projection and housing being rotatable relative to each other; and a selector member connected to the projection, whereby rotation of the housing of the punch tool means relative to the projection causes the selector member to selectively engage one or more of the punch pins.

12. A punch press as claimed in claim 11 wherein the punch pins are located in respective bores in a block member within the housing and are each movable axially between their engaged and disengaged positions.

13. A punch press as claimed in claim 1, further comprising a die assembly adapted to be removably mounted to the punch press housing and having a transfer plate member for transferring material between punching operations via a rotary motion and a retaining plate member for retaining the transfer plate member and having an aperture therein to accommodate punching operations.

14. Clamping means for holding a workpiece in a punch press having a workpiece carrier mechanism, the clamping means comprising a first portion adapted to be mounted to the carrier mechanism; a second portion connected to the first portion and having means for clamping an edge of the workpiece, the second portion being pivotally coupled to the first portion such that the second portion is able to make a complementary movement to distortionary movement of the workpiece due to punching or other working thereof.

15. A punch press as claimed in claim 14 wherein the first and second portions are connected by at least one link member which is pivotally coupled to both.

16. A relocatable clamp for use in holding a workpiece in a punch press having a workpiece carrier mechanism, said clamp comprising a first pair of jaws for holding a portion of the workpiece therebetween; a second pair of jaws for clamping onto the carrier mechanism; both the first and second pair of jaws being selectively operable by jaw control means on the clamp; and actuating means located on the punch press, whereby when the clamp is positioned to locate the jaw control means in registry with the actuating means, the jaw control means can be actuated to release the first and second pairs of jaws and permit the clamp to be relocated relative to the workpiece.

17. A relocatable clamp as claimed in claim 16, wherein the jaw control means comprises a valve member and the first and second pairs of jaws are hydraulically operated via the valve member, the valve member being operable by a piston rod having one end protruding from the clamp, and wherein the actuating means comprises an extendible member for engaging the piston rod and operating the valve member.

18. A relocatable clamp as claimed in claim 17 wherein the actuating means is controlled by a computer- based control circuit for the punch press.