GB2270871A - Operation of press tools - Google Patents

Abstract

There is disclosed a press tool system and a method of operation thereof. The method allows the throughput of the system to be maximised by adjusting feed start and stop points (FFS, FE) in an operating cycle to occur, respectively, as soon as possible after a tool clears a workpiece and as soon as possible before the tool contacts the workpiece. The system may be adaptive, the method including steps of measuring the delays which occur after the start and stop signals before the feed mechanism is affected, and adjusting the timing within the cycle accordingly. <IMAGE>

Description

OPERATION OF PRESS TOOLS The present invention relates to operation of press tools.

Press tools are commonly used in the production of articles from workable material, most commonly metal.

In its most basic form, a press tool usually has a tool comprising a punch arranged for cyclical movement towards and away from a co-operating die, and a feed mechanism. The feed mechanism is operative to position a workpiece in the tool between the punch and the die and retain it there while the punch moves towards the die. As the punch moves towards the die it makes contact with the workpiece retained therebetween and performs the intended operation on the workpiece which may for example include a plastic deformation, or a shearing or a punching operation. Thereafter, the punch moves away from the die and the feed mechanism removes the workpiece from the machine, generally and the operating cycle is then repeated. There may be means to remove the worked workpiece from the operating site of the punch, such means commonly comprises a stripper plate.

It will be appreciated that it is of the utmost importance that the feed mechanism does not attempt to move the workpiece while it is in contact with the punch, or when moving the workpiece would cause it to foul on any part of the tool. If the workpiece does foul the operation of the machine it could cause damage to the workpiece or to the press tool itself. Thus, a control system must be provided to ensure that the feed mechanism is activated at the correct point in the cycle of movement of the punch.

In known press tools the operation of the feed mechanism is typically controlled by switches activated by cams driven from a reciprocating or rotating part of the machine such as a crank shaft, the motion of which is linked to that of the punch. When the press tool is first set up and whenever the punch, die, or thickness of the workpiece is changed, the switches and cams must be adjusted to ensure that the feed mechanism is started as soon as possible after the workpiece is free to move without fouling the tool. However, since this setting-up is done entirely manually, there is an inevitable lack of precision due, primarily, to the need to leave a safety margin. This reduces the maximum throughput of the machine since for a part of each cycle the machine is idle - neither feeding nor forming a workpiece.If this idle time can be reduced then the cycle frequency of the press tool may be increased so increasing its throughput. This has been known for very many years, but the consequences of mis-setting the cams is potentially disasterous and so it is accepted in the art that there will be of necessity a wide and unknown safety margin.

A further disadvantage of the known system is that it is difficult to quantify the required settings to allow them to be set by reference to a routine formula.

Rather, the setter generally relies on experience which means that the setting of the machine becomes a "black art" which can be very inconvenient if the person trained to set the machines becomes, for any reason, unavailable for work. Also, this makes any quality checking on the accuracy of the settings virtually impossible. It also makes it extremely difficult for managers of press tool lines to put pressure on cam-setters to set the machines more efficiently - who can say if the cam setter could get more out of the machine safely? It is the aim of the present invention to provide an improved system for controlling the operation and set-up of a press tool to overcome or ameliorate the disadvantages of known systems.

According to a first aspect of the invention we provide a press tool system comprising a tool, feed means feeding workpieces to be worked into the tool, and control means, the control means controlling the timing of the operation of the feed means relative to the operation of the tool and comprising computer means, microprocessor means, or the like.

Preferably the timing of the operation of the feed means can be adjusted whilst the system is working.

Preferably the number of cycles of the tool per unit time can be adjusted whilst the system is working.

A second aspect of the invention comprises a press tool system in which there is feed means the timing of which is adjustable during the operation of the system, or in which the number of cycles of the system per unit time is adjustable whilst the press is operating.

In either aspect of the invention a signal to start the feed means may be generated before the feed path through the tool is clear for the workpiece, the system relying upon there being a delay before the workpiece actually moves into the press.

The system may have parameter input means whereby feed timing parameters are entered into the control means which calculates the timing of the operation of the feed means using the parameters input. Preferably a parameter indicative of the height that the die and/or punch of the tool has to move to provide a clear feed path for the workpiece is input.

Preferably the system has a position sensor which senses the position in its operational cycle of the tool. The position sensor preferably monitors angular position, for example the angular position of a shaft.

According to a third aspect of the invention we provide press means for performing a pressing operation on material fed into an operative, press tool, region by feed means, the press means comprising a pressing tool which moves in a pressing cycle, feed means for feeding material to the operative region, monitoring means for monitoring the position of the tool in its cycle, adjustment means for adjusting the point in the operational cycle of the tool at which the feed means starts or stops, and control means for controlling the adjustment means in response to signals from the monitoring means.

The press means also preferably includes parameter input means which inputs at least one parameter to the control means which automatically calculates the timing of the feed means from said parameter and controls the adjustment means in reponse to said parameter.

According to a fourth aspect of the invention we provide a method of reducing the portion of an operating cycle of a press tool system in which the system is neither feeding a workpiece into the tool, nor actually deforming the workpiece, the method comprising: (a) calculating or monitoring the point at which feed movement of the workpice stops; comparing that point with the latest theoretical time when feed movement of the workpiece would not foul the press; and advancing the actual stopping point towards the theoretical last stopping point by reducing the time the press takes to complete a pressing cycle; or (b) generating a signal to start feed means of the system before the punch of the tool is actually clear of the feed path of the workpiece; or (c) performing both steps (a) and (b).

In a fifth aspect the invention provides a method of setting up a press tool system comprising a press tool in which a punch moves in a cycle towards and away from a die to deform a workpiece placed therebetween and feed means for positioning a workpiece in the tool and subsequently removing it therefrom; the method initially comprising the step of ascertaining a feed-start point in the cycle at which the punch is sufficiently clear of the workpiece to allow feeding to recommence; and subsequently comprising the steps of: operating the press tool in a cycle in which a control signal is generated to commence operation of the feed means, initially at the said feed-start point, and measuring a delay period being the time taken for the feed operation to commence, and in subsequent cycles generating the said control signal at a point in the cycle advanced of the feed-start point by a time not greater than the delay period.

This automatically adjusts the point in the cycle at which the control signal is generated so that feeding movement of the workpiece commences a consistent, short time after the punch has moved clear of the workpiece.

Preferably, the method also further comprises the steps of, initially, determining a maximum operation time for the duration of the feeding operation, and subsequently operating the press tool in a cycle whose period is of such duration that the time between the occurrence of an actual feed-start point and a subsequent theoretical last feed-stop point is greater than said maximum operation time, measuring the actual operation time of the feed mechanism and adjusting the period of the cycle such that the feed operation finishes at a point in the cycle shortly before the theoretical last feed-stop point.

The adjustment of the duration of the press cycle may comprise a separate invention to the adjustment of the point at which the feed begins.

Preferably the determined maximum operation time is an overestimate to ensure that the feed operation has stopped well before the theoretical last feed-stop point, subsequent adjustments reducing the period of the cycle so as to move the point in the cycle at which the feed operation finishes towards the theoretical last feed-stop point.

In this way, the cycle period is reduced (so its frequency is increased) until the non-productive period after the feeding operation is complete is reduced to a minimum value acceptable for safe operation.

Preferably the adjustments made during each cycle are small in comparison to the theoretical maximum adjustment. In this way the limit of adjustment is reached in small steps so as to avoid the risk of overadjustment with the consequence of damage to the machine or workpiece. Alternatively, it is possible to carry out all or substantially all of the adjustment in one step.

In one embodiment, the feed-start position and the feed stop position are ascertained by calculation based on geometrical parameters of the system. By preference, this may be a single parameter representing the distance between a pair of datum points, one on each of the die and punch or parts fast therewith, when the punch is just touching the workpiece. This arrangement allows the press tool to be set up by the taking of a single, simple measurement.

The press tool preferably further comprises a control unit which may be based upon a microcomputer, for example a single-board microcomputer. Such a control unit offers flexibility in its set-up and can be programmed to carry out the computations required during set-up and operation of the press tool.

A control unit of the type described above is preferably provided with a data-entry device such as a keypad by means of which the user can input the parameters required to set up the press tool.

The feed mechanism used in a press tool system according to any aspect of the invention may comprise a linear feed of a continuous workpiece, a pick-and-place feed of discrete workpieces, or any other type of antimetric feed mechanism.

An embodiment of the invention will now be described in detail, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a press tool embodying the invention; Figures 2 and 3 are diagrams showing the significant points in the operating cycle of a press tool embodying the invention respectively when the press tool is first started up and after the timing has been adjusted to its operational setting; and Figure 4 is another representation of the cycle of Figure 3.

With reference to Figure 1 a press tool system 1 operates on a workpiece 10 in the form of a continuous strip of metal unwound from a coil 12. The press tool system 1 comprises feed means 2, a press tool 14, and control means 3. The workpiece is shown in plan as 10'.

The workpiece 10 passes through the tool 14 where a forming operation is performed on it, converting it into a finished or semi-finished article 16, 16'.

The tool 14 is conventional in design. It comprises a fixed support 18 on which is mounted a die 20 and a movable support 22 on which is mounted a punch 24, arranged for reciprocal movement towards and away from the fixed support 18. The punch 24 and die 20 are complementarily shaped so that when the workpiece 10 is placed between them and the movable support 22 (and the punch 24 attached thereto) moves towards the fixed support 18, the workpiece 10 is trapped between the punch 24 and the die 20 and, as the movement of the movable support 22 continues to its limit, is deformed into the desired shape.

In this embodiment, the movable support 22 is driven by a rotating shaft 26 from which a crank arm 28 radially projects. A link 30 is pivotally connected between the crank arm 28 and the movable support 22. By this arrangement, rotational movement of the shaft 26 is converted to rectilinear cyclic movement of the movable support. It will be appreciated that one complete cycle of movement of the movable support 22 corresponds exactly to a complete rotation of the shaft 26. It is therefore convenient to define points within the cycle of the movable support 22 in terms of the angular position of the shaft. For the purposes of the following, the shaft angle will be denoted T.

The press tool also comprises the feed means 2 which may also be conventional in form. Typically, a tandem air feed may be used which comprises a pair of actuators 32, 34 which operate in turn to clamp the workpiece and advance it through the press in a stepwise fashion. The feed means 2 is controlled by the control means 3.

Also provided. are movement detectors 36 of any suitable form which generate a signal responsive to movement of the actuators 32, 34 (and thus also the workpiece 10). The signals from movement detectors 36 are fed to the control means 3.

The control means 3 can conveniently be based upon a single-board microcomputer. The control means receives an input signal from the movement detectors 36 and an input signal from a position-detecting sensor 9 which monitors the angular position of the shaft 26 and provides a signal indicative of the angular position T of the shaft 26. The control means 3 generates output signals to control operation of the feed means 2 and to adjust the cycle frequency of the press. The system 1 also has an input device, such as a keypad 4, by means of which an operator can input parameters into the control means and can control operation of the press tool. The parameters entered via the keypad 4 include data concerning the punch, die, and workpiece. The system also has a display screen 5 which displays information to the operator of the machine.

The sequence of operation of the press tool embodying the invention will now be described with reference to Figures 2 to 3.

The complete operational cycle of a press tool is represented in Figures 2 and 3. A complete clockwise traverse of the circle represents a whole cycle and each point around the circle uniquely identifies a point in the cycle. In the present embodiment, the angular position of a point on the circle may represent the angular position of the shaft 26. However, these timing diagrams can be applied to other embodiments not incorporating a crank where the angle T simply represents an arbitrary measurement starting at 0 at the start of the cycle and counting up to 3600 at the end of a cycle. The bottom dead centre position is represented at point BDC.

When a punch 24 and die 20 are first mounted on the tool or when the size or shape of workpiece is changed, the operator must first supply the control unit with a parameter representing the geometry of the workpiece 10, punch 24 and die 20. Most conveniently, this parameter will be the distance between datum points on the punch 24 and die 20 when an undeformed workpiece is just clamped between the punch 24 and die 20 or is just clear of them. The datum points are arranged to be in a predetermined position relative to the fixed and workable supports 18, 22 when the punch 24 and die 20 are mounted on the tool. This parameter is illustrated graphically in Figure 2 by the distance ID. While the shaft 26 is at an angle which falls in the band ID at the bottom of the cycle any movement of the workpiece will foul the system.

Since the geometry of the press is known and constant, the parameter ID can be used to calculate a feed-stop angle T1 of the crank 26 at which the punch just touches the workpiece 10 and a feed-start angle T2 at which the punch 24 just comes out of contact with the workpiece 10. The angles T1 and T2 are calculated automatically by the control unit from the parameter ID (which is input via the keypad 4) using well-known rules of the kinematics of linkages. The exact method of calculation will, of course, vary from one press design to another.

Instead of putting the parameter ID via the keypad 4 the system could measure it itself when a test piece is placed between the die and the mandrel.

The control means 3 must also be made aware of the maximum time taken for the feed mechanism to perform its feeding operation. This may be pre-programmed through knowledge of the operational characteristics of the feed means, automatically by the system measured in a test, or may be entered by an operator via the keypad 4. For example the operator may time the feed operation manually and enter that time. The duration of feed and speed of rotation of the shaft 26 determine the angular length of the feed duration on the cycle of Figures 2 and 3. Alternatively or additionally the system may be run initially without a workpiece and the delay between application of the feed start signal and commencement of feeding and duration of feeding can be measured by the control means 3.This timing information can be used to provide a starting estimate or can be used to calculate limiting conditions for the operation of the system, since it will be known that the feed operation may be slowed down by the presence of a workpiece but will not be speeded up.

Once the ID and feed duration are known the control unit can then start operation of the press tool. Initially, the press tool is operated with timing as shown in Figure 2. In the initial cycle (or cycles) the control signal to start operation of the feed mechanism is generated at a point Feed Start Point (FSS) corresponding to shaft angle T2. Thus it is known with certainty that the feed will not start until after the punch 24 is clear of the workpiece 10. The cycle frequency (speed of shaft 26) is controlled by the control means 3 and is chosen such that the maximum period of operation of the feed mechanism elapses at a point (Feed End Experimental) (FEx) well before angle T1. Thus a clear safety margin ensures that feed has stopped before the punch 24 once more touches the workpiece 10. This initial cycle is shown in Figure 2.

The control means monitors operation of the press tool. By means of the movement sensors 36 it detects the commencement of movement of the feed means. Due to signalling delay, and more importantly inertial delays, this will be some time after the point FSS, and is represented in Figure 2 as point Feed Commences (FC).

By detection of the crank angle T at this instant a switching delay time (FC-FSS) and delay angle (Td) is calculated by the control means.

The control means 3 also detects the instant Feed End (FE) at which feeding is complete. This will generally be some time before FEX. The angle turned by the crank between actual feed-stop and start will be denoted Tf.

Once the control unit has established the actual operating parameters of the press tool it can adjust the timing to improve the efficiency of the cycle. Two adjustments can be made. Firstly, the instant FSS at which the feed start signal is generated can be brought forward in the cycle, such that the actual feed start FS takes place more closely following the instant (T1) at which the punch 29 breaks contact with the workpiece 10. This means that the Feed Start Signal is generated before the cycle reaches angle T2, i.e.

before punch clears the distance ID. Secondly, the point in the cycle FE at which the feed actually stops can be made to approach the latest point, at angle T1, at which it must end. Since the time taken to complete the feed operations is fixed, this movement of FE towards T1 is achieved by increasing the cycle frequency (speed of operation of the press tool).

It will be appreciated that the angular positions T1, and T2 are fixed since they are dependant only on the geometry of the press, punch 24, die 20, and workpiece 10 (and sometimes upon other fixed things, such as the thickness of any stripper plates). However, the time taken to feed the workpiece is fixed, irrespective of the frequency of the cycle, so the angles Tf and To will increase as the cycle frequency increases.

In case there is any possible measuring error the timing is adjusted in relatively small iterative steps, measurements of the performance of the press tool being made after each adjustment, until it is calculated that the feed start angle T5 approaches T1 and that the feed and angle Te approaches T2 near as possible with a reasonable margin of safety. The margin of safety can be pre-programmed into the system, or at least a minimum safety margin may be pre-programmed.

Figure 3 shows the timing of the press tool after several iterations, when the feed timing and press tool cycle speed have reached their stable, desired values for that particular run. Of course, the system could alternatively be arrnaged to go straight to the desired final timing diagram, in one or two large jumps, instead of a series of smaller steps.

The continued measurement and adjustment also allows for changes in the operating speed of the feed mechanism, due for example to wear or a variation in air pressure, to be compensated for without the need to build unnecessarily large fixed margins of safety into the system timing.

A further matter which must be taken into account when the timing is adapted is that a press tool will generally be restricted in its maximum safe rate of operation. The maximum value will preferably be pre-programmed into the control means 3 which will not increase the cycle frequency such that the maximum is exceeded.

The system may even have a variable speed feed mechanism, signals or parameters indicative of the speed of feed then being fed to the control means so as to allow the timing diagram of Figure 3 to be calculated properly.

The display screen 5 is a LCD display and is controlled by the control means 3O display the cycle of Figure 3, showing the working quadrant (FS to FE), the switch points FSS and the point at which the signal to end the feed is generated (not shown on Figure 3, but a little before FE), FS, FE, and possibly the value of any control parameters entered. The feed motion angle may also be displayed to show its relationship with the working quadrant. The feed length may be displayed, as may the batch count and/or total count of articles in a run.

An important feature is that the operator can alter the setting of the timing of the feed of the speed of the press (cycles per minute), or both, whilst the press tool system is operating. If the user wishes to produce, say 200 articles a minute the feed timing diagram may look like that of Figure 3, with say 300 between FE and T1. If the user wants to make 240 articles a minute he can increase the speed of the system (provided that any maximum operation speed is not exceeded) to make the press operate faster so that FE advances closer towards T1. This adjustment can be made whilst the press is producing articles. The user maybe able to input via keypad 4 the number of articles required in a set time.

The control means will remember any input or measured parameters upon power-down of the system if the user wishes it to. Alternatively the user can clear the memory of the control means, re-setting it.

The display may represent the cyclical display of Figure 3 as a. linear graph (see Figure 4), at the choice of the user.

Claims (18)

1. A press tool system arranged for cyclic operation in cycles in which there is feed means the timing of which is adjustable during operation of the system or in which the number of cycles of the system per unit time is adjustable during operation of the system.

2. A press tool system according to claim 1 having a control means operative to generate signals to control the feed means.

3. A press tool system according to claim 2 in which a signal to start the feed means is generated before the feed path through the tool is clear for the workpiece.

4. A press tool system according to claim 2 having parameter input means whereby at least one feed timing parameter may be entered into the control means, the control means being operative to calculate the timing of the operation of the feed means using the parameters thereby input.

5. A press tool system according to claim 4 in which one such parameter is indicative of the height that the die and/or the punch tool must move to provide a clear feed path for the workpiece.

6. A press tool system according to any preceding claim having a position sensor operative to sense the position in its cycle of the tool.

7. A press tool system according to claim 6 in which the position sensor senses the position of a rotating component of the system.

8. A press tool system substantially as described herein with reference to the accompanying drawings.

9. Press means for performing operation on material fed into an operative press tool region thereof by feed means, the press means comprising a pressing tool which moves in a pressing cycle, feed means for feeding material to the operative region, monitoring means for monitoring the position of the tool in its cycle, adjustment means for adjusting the point in the operational cycle of the tool at which the feed means starts or stops, and control means for controlling the adjustment means in response to signals from the monitoring means.

10. Press means according to claim 9 having parameter input means operative to receive as input and to pass to the control means at least one parameter, the control means being operative to control the adjustment means in response to the said parameter.

11. A method of reducing the portion of an operating cycle of a press tool system in which the system is neither feeding a workpiece into the tool, nor actually deforming the workpiece, the method comprising: (a) calculating or monitoring the point at which feed means movement of the workpiece stops; comparing that point with the latest theoretical time when feed movement of the workpiece would not foul the press; and advancing the actual stopping point towards the theoretical last stopping point by reducing the time the press takes to complete a pressing cycle; or (b) generating a signal to start feed means of the system before the punch of the tool is actually clear of the feed path of the workpiece; or (c) performing both steps (a) and (b).

12. A method according to claim 11 further comprising the steps of, initially, determining a maximum operation time for the duration of the feeding operation, and subsequently operating the press tool in a cycle whose period is of such duration that the time between the occurrence of an actual feed-start point and a subsequent theoretical last fee-stop point is greater than said maximum operation time, measuring the actual operation time of the feed mechanism and adjusting the period of the cycle such that the feed operation finishes at a point in the cycle shortly before the theoretical last feed-stop point.

13. A method according to claim 12 in which the determined maximum operation time is an overestimate to ensure that the feed operation has stopped well before the theoretical last feed-stop point, subsequent adjustments reducing the period of the cycle so as to move the point in the cycle at which the feed operation finishes towards the theoretical last feed-stop point.

14. A method according to any one of claims 11 to 13 in which the adjustments made during each cycle are small in comparison to the theoretical maximum adjustment.

15. A method according to any one of claims 11 to 13 in which substantially all of the adjustment is made in one step.

16. A method according to any one of claims 11 to 15 in which the feed-start position and the feed-stop position are ascertained by calculation based on one or more geometrical parameters of the system.

17. A method according to claim 16 in which the or one of the said parameters represents the distance between a pair of datum points, one on each of the die and punch or parts fast therewith, when the punch is just touching the workpiece.

18. A method of operating a press tool system substantially as described herein with reference to the accompanying drawings.