EP0597212B1 - Method of controlling a punch press during starting and stopping - Google Patents

Abstract

In order to reach the operating speed of rotation from a standstill, the eccentric shaft (5) must, owing to forces arising from the mass moment of inertia, be accelerated to the number of operating strokes via a starting angle ( alpha B). When the punch press is brought to a standstill, the eccentric shaft (5) is rotated in the operating direction of rotation (13) to a position between the upper dead centre (OT) and the lower dead centre (UT), in which position there is no contact between the upper tool (8) and the metal belt (12). From this position, the eccentric shaft (5) is rotated backwards through the starting angle ( alpha B) to a starting angle position (D). In the starting angular position (D) there is also no contact between the upper tool (8) and the belt (12). There is therefore available for the starting of the punch press a starting angle ( alpha B) which is extended beyond the upper dead centre (OT) so that the first punching operation is executed under the same dynamic conditions of the punch press as the following punching operations, which means that accurate parts are produced on starting, from the very first stroke. <IMAGE>

Description

The invention relates to a method for operating a punch press when starting and stopping the same, which punch press is driven by a positionable drive via the clutch unit of a clutch / brake device, an eccentric shaft, a ram driven by the eccentric shaft for carrying at least one upper tool and a press table for carrying at least one Has lower tool, by means of which tools a strip-shaped workpiece arranged in between is machined, which punching press passes through a starting angle due to the overall moment of inertia of the moving components and the drive torque transmitted by the coupling unit to the eccentric shaft for acceleration from standstill to the operating stroke number and the contact between the tools and the belt starts at a given working angle position of the eccentric press. Such a method is known from US-A-4 653 311.

In the case of high-speed punching machines, the known increase in the inertial forces of the accelerated components as the speed increases is a problem which has an influence in particular on the quality and accuracy of the products produced with such punching machines. Due to the accelerations and decelerations of the predominantly oscillating components and the opposing forces that arise during the machining of a respective workpiece, the punching machine and in particular its moving components suffer elastic deformations, and furthermore there are displacements in the bearings, which conditions have a negative effect on manufacturing accuracy.

The manufacturing accuracy of a stamped product is heavily dependent, among other things, on the respective ram height of the machine. As is generally known, this ram height determines the tool closing height or the immersion depth when the machine is in operation.

If an unchanging ram height is specified for given embossing and cutting work at a given number of strokes, e.g. with a smaller number of strokes the embossments are not deep enough, with a higher number of strokes the embossments are too deep or the immersion depth of the tool stamps is too large, which is known to lead to undesirably large wear of the corresponding tool parts.

Various procedures have become known for regulating the ram height or immersion depth based on the number of strokes. For example, reference is made to CH-A-676 445.

When punching, in particular with follow-up cutting tools, there should also be no rejects caused by the inertia forces mentioned above when starting and stopping the punching machine, and starting and stopping in particular with high-speed punching machines causes problems in this regard.

To start the punching machine, the eccentric shaft is drive-connected by closing the clutch with the drive located at the operating stroke number, in particular the flywheel, and thus accelerated from standstill to the operating speed. The dynamic behavior of the punch press during the first machining process, e.g. The punching process is defined as the first punch behavior, and it is this first punch behavior that determines the quality of the first punched part.

In known starting methods of high-speed punch presses, the first punch behavior is such that the first punching process does not take place with the number of operating strokes like the subsequent punching processes, i.e. that the dynamic behavior of the machine is not the same for the first and subsequent strokes, which has a negative effect on the accuracy of the first part.

A reduction in the number of operating strokes eliminates this disadvantage, but reduces the production, ie Number of pieces produced within a given period of time.

The invention seeks to remedy this. The invention, as characterized in the claims, solves the problem of creating a method for operating a punch press when starting and stopping the same, in which after the stop has been completed, the eccentric shaft is rotated back into a starting angle position according to which it is started again after it has been run through of the approach angle for accelerating to the operating stroke number is on the operating stroke number before the first machining contact takes place between the tool and the workpiece.

The advantages achieved by the invention are essentially to be seen in the fact that the first punch stroke takes place with a dynamic behavior of the punch press which is the same as the dynamic behavior in continuous operation. This means that when starting up, the strip to be processed is precisely machined during the first machining stroke, so that no rejects are produced.

• Figur 1 zeigt schematisch eine Stanzpresse mit den das Verständnis der Erfindung erleichternden Baueinheiten,
• Figur 2 zeigt ein Diagramm, in dem das Anfahrverhalten eine Stanzpresse dargestellt ist,
• Figur 3 zeigt schematisch die Stellung einer nach dem erfindungsgemässen Verfahren betriebenen Stanzpresse nach dem Stillsetzen, und
• Figur 4 zeigt schematisch die Stellung einer nach dem erfindungsgemässen Verfahren betriebenen Stanzpresse vor dem Anfahren.

The invention is explained in more detail below with the aid of drawings which illustrate only one embodiment.

• FIG. 1 schematically shows a punch press with the structural units that facilitate understanding of the invention,
• FIG. 2 shows a diagram in which the starting behavior of a punch press is shown,
• Figure 3 shows schematically the position of a punch press operated according to the inventive method after stopping, and
• Figure 4 shows schematically the position of a punch press operated according to the inventive method before starting.

Figure 1 shows schematically a punch press. It has a positionable drive 1. This drive 1 contains an electric motor which can be controlled in any desired angular position and which drives the flywheel of the high-speed punch press according to generally known designs via a belt drive. The flywheel is connected to a clutch / brake device 2, 3, which in turn is connected to the eccentric shaft 5, which is mounted in the machine frame 4.

The clutch / brake device 2, 3 has a clutch unit 2, by means of which the eccentric shaft 5 can be coupled or uncoupled from the drive 1, or its flywheel, and has a brake unit 3 with a brake disc 14, via which Brake disc 14, the eccentric shaft 5 can be braked against the machine housing 4. Details of this braking device can be found in CH-A-546 141 and US-A-3 805 931. It should be noted here that the clutch unit 2 and the brake unit 3 are non-positive designs, i.e. they grind when engaging or braking.

On the eccentric shaft 5 connecting rods 6 are articulated, which carry the tappet 7. This plunger 7 is connected to the upper tool 8. The press table 10, which carries the lower tool 9, is also shown in FIG. Reference numeral 11 generally designates the balance weight arrangement for balancing the rotating and oscillating forces occurring during the operation of the punch press.

In operation, the eccentric shaft rotates through all angular positions of a 360 ° angle and can obviously assume any angular position driven by the positionable drive at a standstill. An upper dead center UD and a lower dead center LD are generally defined for the eccentric shafts 5 of the stamping presses, the articulation point of the connecting rod (s) on the eccentric shaft 5 being taken as the structural reference. At the top dead center UD, the tappet 7 has the largest at the bottom dead center LD the smallest distance from the press table 10. These positions UD and LD can be seen from FIGS. 3 and 4.

To interrupt operation, a punch press is usually shut down or positioned approximately at top dead center UD. The distance between the ram 7 and the press table 10 has the greatest value, the tool (consisting of upper tool 8 and lower tool 9) is open. When operation is interrupted, the clutch unit 2 is opened and the brake 3 is closed, i.e. the eccentric shaft 5 is uncoupled from the drive 1, the drive 1 with the flywheel idling at the operating speed and the crankshaft 5 stopped.

Reference is now made to FIG. 2. The abscissa relates to the angular position α of the eccentric shaft 5, the ordinate to the speed n of the same.

M =

von der Kupplung abgegebenes Antriebsmoment [Nm],

J =

Massenträgheitsmoment der bewegten Bauteile der Stanzmaschine [kgm²]

α =

Anfahr- bzw. Bremswinkel [°].

If, when the eccentric shaft is stationary and the drive is running at the operating speed n _B , the brake is opened and the clutch to the eccentric shaft located in the top dead center position UD is closed, the speed n of the eccentric shaft increases under the influence of the torque transmitted from the clutch to the eccentric shaft. This increase in the speed n relative to the angular position α is shown in FIG. 2 by the curve line. After a certain period of time, ie after passing through a certain angle of rotation α, the operating speed n is reached. The speed change takes place according to the formula $$\text{n =}\sqrt{\frac{\text{α. M. 10th}}{\text{J. π}}}\text{, in which}$$

M =

drive torque given by the clutch [Nm],

J =

Mass moment of inertia of the moving components of the punching machine [kgm²]

α =

Approach or braking angle [°].

The tool closure, ie the machining contact between the upper tool and the strip to be processed, takes place shortly before bottom dead center LD, at which the eccentric shaft has passed through an angle of rotation or approach angle α _A , the distance between the approach angle being shown in the diagram in FIG α _A and α = 180 ° can be seen.

Thus must the Betriebshubzahl n _A at the latest when actuating α _A may be achieved if the first punch when starting with the same dynamic conditions to be executed, as in the next punching. There are therefore no difficulties with any operating stroke number ≦ n _A.

However, if the Betriebshubzahl n _B over n _A, ie n _B ≧ n _A, which property is dominant in high-speed punching presses, an actuating α _B is required, which is greater than α _A is, if back in the first punching the same dynamic conditions as in the following die cuts should prevail.

The same considerations apply when stopping the punch press. A reduction in the number of strokes may only be initiated after passing through the bottom dead center LD, the complete standstill before a 360 ° rotation before the tool and the metal strip have come into contact.

The parameters M (drive torque or braking torque) and J (moment of inertia) of a punch press can only be changed with difficulty or not at all. The method according to the invention is thus used, which will now be described with reference to FIGS. 3 and 4.

Since the operating speed n and the machine parameters M and J are known, both the approach angle α _B and, accordingly, the braking angle can be calculated in a control unit for the punch press.

nach dem oberen Totpunkt UD liegt.When stopping, the punch press is not stopped at top dead center UD, but at the angular position C, which $\frac{\text{αB}}{\text{2nd}}$

after top dead center UD.

maximal so gross sein, dass ein Erreichen des unteren Totpunktes LD und somit eine weitere Stanzung vermieden ist. Beim Stillsetzen einer Stanzpresse wird die Kupplung geöffnet und die Bremse geschlossen, wobei der Antrieb mit dem Schwungrad immer noch mit der Betriebsdrehzahl weiter rotiert.Obviously, may $\frac{\text{αB}}{\text{2nd}}$

maximum so large that reaching bottom dead center LD and thus further punching is avoided. When a punch press is stopped, the clutch is opened and the brake is closed, the drive with the flywheel still rotating at the operating speed.

rückwärts in die Winkelstellung D nach Figur 4 rotiert. Nach dem Erreichen der Winkelstellung D wird die Kupplung 2 geöffnet und der Antrieb 5 auf die Betriebsdrehzahl n_B hochgefahren. Die Exzenterwelle 5 steht in der Winkelstellung D und damit steht die stanzpresse für ein Einkuppeln und Anfahren mit einem verlängerten Anfahrwinkel α_B bereit.After stopping the punch press, ie the eccentric shaft, the drive is now also stopped. Then the drive is set in motion in the opposite direction, the eccentric shaft is engaged and thus by the angle $$\text{2 x}\frac{\text{αB}}{\text{2nd}}\text{= αB}$$

rotated backwards into the angular position D according to FIG. After reaching the angular position D, the clutch 2 is opened and the drive 5 is raised to the operating speed n _B. The eccentric shaft 5 is in the angular position D and the punch press is thus ready for engaging and starting with an extended approach angle α _B.

Normally, a punch press is stopped at top dead center UD so that it can be manipulated in the open tool. The press can thus be stopped at top dead center UD when rotating back from point C to point D (intermediate stop).

Claims (4)

1. Method of operating a punch press during the operation start-up and stopping cycle, which punch press includes a positionable drive (1), driving a coupling unit (2) of a coupling/brake device (2;3) to an eccentric shaft (5), a ram (7) to be driven by the eccentric shaft (5), at least one upper tool (8), mounted to the ram (7), and a punch press table (10) with at least one lower tool (9) mounted to the punch press table (10), and with said upper and lower tools (8;9) a striplike workpiece (12) located therebetween is worked upon, whereby the punch press, due to the total inertia moment of the moving structural members and due to the driving torque transmitted by the coupling unit (2) to the eccentric shaft (5) rotates during the acceleration from the standstill state to the state of rotating at the operational rated number of strokes through a start-up angle (α_A), and where a contact between the tools (8,9) and the striplike workpiece (12) occurs at a predetermined operation angle position (C) of the eccentric shaft (5), characterized in that after the punch press has been brought to a standstill, the eccentric shaft (5) is rotated for a subsequent start-up to a start-up angle position (D) without passing through its lower dead center position (LD) according to which start-up angle position the eccentric shaft will be located at a subsequent start-up, after having rotated through the start-up angle (α_B) in the normal operating direction of rotation and has the rated operational speed, ahead of the operation angle position (C).
2. Method of claim 1, in which the contact between the working tools (8;9) and the striplike workpiece (12) ends at a predetermined release angle rotational position and after the rotation in the normal operating direction (13) of rotation past the lower dead center position (LD), and where with the stopping cycle of the punch press, the eccentric shaft (5), due to the total inertia moment of the moving structural members and due to braking torque applied by the braking unit (3) of the coupling/brake device (3;4) rotates for a deceleration of the rotational speed of the eccentric shaft (5) from the operational rated number of strokes to the state of standstill through a stopping angle, characterized in that the deceleration of the rotational speed of the eccentric shaft (5) is initiated by the braking unit (3) immediately after passing the release angle rotational position (D) in the direction of the normal operating direction of rotation.
3. Method of claim 1 or 2, wherein the stopping angle (α_A) is larger than the angle between the release angle rotational position and the upper dead center position (UD) of the eccentric shaft (5) measured in the direction of the normal operating direction of rotation (13), characterized in that the eccentric shaft (5) is rotated back into the start-up angle position (D) by a operation of the positionable drive (1) in a direction opposite to the normal operating direction of rotation and through the upper dead center position (UD).
4. Method of one of the foregoing claims, characterized in that the eccentric shaft during rotating back into the start-up angle position (D) is temporarily stopped in the upper dead center position (UD).

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