CH717506B1 - Method for actuating a lifting door in a machine tool and machine tool with a lifting door. - Google Patents

Abstract

The invention relates to a method for actuating a lifting door (8a; 8b) in a machine tool. The lift gate (8a; 8b) is designed to open and close vertically between a first position (B) in which the lift gate (8a; 8b) is fully closed and a second position (A) in which it is fully opened , by means of one or more pneumatic piston-cylinder arrangements with first cylinder chambers (9a; 9b) and second cylinder chambers (10a; 10b) working in opposite directions. An enlargement of the first cylinder chambers (9a; 9b) starting from the first position (B) causes a reduction in the size of the second cylinder chambers (10a; 10b) and a displacement of the lifting door (8a; 8b) in the direction of the second position (A). and vice versa, an enlargement of the second cylinder chambers (10a; 10b) starting from the second position (A), a reduction of the first cylinder chambers (9a; 9b) and a displacement of the lifting door (8a; 8b) in the direction of the first position (B). . The first cylinder chambers (9a; 9b) and the second cylinder chambers (10a; 10b) are moved both when the lift gate (8a; 8b) is moved from the first position (B) to the second position (A) and when it is moved from the second position Position (A) to the first position (B) with compressed air. This has the advantage that the lifting door (8a; 8b) is always clamped between the first and second cylinder chambers (9a, 10a; 9b, 10b) when moving between the fully closed position (B) and the fully open position (A). and can be opened and closed in a controlled manner.

Description

TECHNICAL AREA

The present invention relates to a method for actuating a lifting door in a machine tool and a machine tool with a lifting door according to the preambles of the independent claims.

STATE OF THE ART

In automated machine tools, such as punching machines, the machining area is usually isolated from the environment and is only accessible for maintenance and assembly work via service doors. These doors are usually designed as sliding or lifting doors, which are moved horizontally or vertically to open and close. In the case of vertically sliding lifting doors, the weight of the door must be absorbed by the door drive. In the case of smaller lifting doors, the weight of the door is often compensated with gas pressure springs, which, however, lose their spring force over time. With larger lifting doors, it is now customary to actuate the lifting doors by means of pneumatic piston-cylinder arrangements with first and second cylinder chambers working in opposite directions, with which the doors can also be locked pneumatically in the open and in the closed position. To raise the lifting doors, compressed air is applied to the first cylinder chambers, while the second cylinder chambers are switched to atmosphere. To lower the lifting doors, when the first cylinder chambers are pressurized with compressed air, the second cylinder chambers are pressurized with compressed air at a precisely defined pressure via a pressure control valve, which is set during commissioning in such a way that a specific closing force or a specific closing speed results.

Apart from the fact that with the systems known today, setting the closing force is relatively difficult and requires a lot of experience, there is also the decisive disadvantage that the closing force or the closing speed of the lifting door depends on the system pressure in the compressed air network and with varying pressure system pressure is not constant. The systems known today also have the disadvantage that the opening speed of the lifting door cannot be adjusted, or can only be adjusted relatively roughly, and is also dependent on the system pressure.

PRESENTATION OF THE INVENTION

The task here is therefore to provide a technical solution which does not have the disadvantages of the prior art described above or at least partially avoids them.

[0005] This object is achieved by the subject matter of the independent patent claims.

According to this, a first aspect of the invention relates to a method for actuating a lifting door in a machine tool, preferably in an automatic punching machine.

The lifting door for opening and closing in the vertical direction between a first position in which it is fully closed, and a second position in which it is fully open, by means of one or more pneumatic piston-cylinder assemblies with counteracting claimed process first and second cylinder chambers.

The piston-cylinder arrangements are designed in such a way that an enlargement of the first cylinder chambers, starting from the first position, causes a reduction in the second cylinder chambers and a displacement of the lifting door in the direction of the second position, and vice versa, an enlargement of the second cylinder chambers, starting from the second position causes a reduction in the size of the first cylinder chambers and a displacement of the lift gate towards the first position.

The first cylinder chambers and the second cylinder chambers are acted upon both when the lifting door is moved from the first position to the second position and when the lifting door is moved from the second position to the first position with compressed air.

This results in the advantage that the lifting door is always clamped between the first and second cylinder chambers when moving between the fully closed position and the fully open position and can be opened and closed in a controlled manner.

In a preferred embodiment of the method, the first cylinder chambers are subjected to compressed air at a first pressure both when the lifting door is moved from the first position to the second position and when the lifting door is moved from the second position to the first position, while the second cylinder chambers when moving the lifting door from the first position to the second position and/or when moving the lifting door from the second position to the first position with compressed air at pressures which differ from the first pressure. This results in the advantage that only the pressure in the second cylinder chambers has to be varied in order to control the upward and downward movement.

For this purpose, the second cylinder chambers are preferably pressurized with compressed air via a servo-pneumatic valve (proportional valve), in particular via an electro-pneumatic pressure control valve. With such valves, the pressure in the second cylinder chambers can be adjusted to any desired pressure between atmospheric pressure and supply air pressure (system pressure) and the second cylinder chambers can preferably also be shut off. When using valves of this type, any pressure fluctuations in the compressed air network no longer have any effect on the function of the lifting gates and the speed of movement of the lifting gate can be influenced in a targeted manner.

Advantageously, the second cylinder chambers are acted upon when moving the lifting door from the first position to the second position with compressed air at a second pressure, which is different from the first pressure, and when moving the lifting door from the second position to the first Position with pressurized air at a third pressure different from the first pressure and the second pressure.

In a further preferred embodiment of the method, the first cylinder chambers and the second cylinder chambers are subjected to compressed air, which is provided by a common compressed air source with a system pressure. As a result, the outlay in terms of plant engineering can be kept low.

Preferably, the lifting door is moved vertically upwards when moving from the first, fully closed position to the second, fully open position. This makes it possible in a simple manner to remove the lifting door completely from the machine operator's field of action.

In process variants in which the second cylinder chambers are subjected to different pressures (second and third pressures according to the claims) depending on the direction of movement of the lifting door, it is preferable for the first pressure to essentially correspond to the system pressure of the compressed air supply system and for the second and the third pressure are lower than the system pressure. This gives the advantage that only a single compressed air source is required.

It is also preferred that the lifting door is pneumatically braced in the first, fully closed and/or in the second, fully open position and is thus secured against externally determined opening or closing.

In yet another preferred embodiment of the method, the pressures in the first and second cylinder chambers are selected when moving the lifting door from the second position to the first position such that the lifting door is closed with a specific closing force, preferably with a closing force between 100N and 200N, more preferably between 140N and 160N. Such a limitation of the closing force is desirable for safety reasons.

It is advantageous that to determine the pressures that are required in the cylinder chambers to achieve the specific closing force of the lifting door, the pressures in the first cylinder chambers and the second cylinder chambers are in an intermediate position between the first position and the second Position arranged lifting door are temporarily adjusted so that the lifting door is in suspension, and then based on these pressures or pressure ratios and the known effective piston areas of the first cylinder chambers and second cylinder chambers, the pressures are calculated at which the lifting door with the specific closing force is closed. This step preferably takes place when the machine is started up, and the calculation of the pressures is preferably carried out by the machine controller.

In yet another preferred embodiment of the method, the pressures in the first cylinder chambers and the second cylinder chambers are selected such that when the lift door is moved between the first, fully closed position and the second, fully open position, the lift door moves at a specific speed is opened and/or closed at a certain speed. This is also desirable for safety reasons.

According to a variant of the method according to the invention, it is also provided to stop the lifting door in an intermediate position between the first position and the second position and to clamp it temporarily pneumatically, e.g. to carry out cleaning work on a viewing window of the lifting door.

A second aspect relates to a machine tool, preferably an automatic stamping machine, with a lifting door which can be selectively opened or closed, preferably while carrying out the method according to the first aspect of the invention, for selectively making the machining area of the machine tool accessible or non-accessible.

The lift gate can be opened and closed vertically between a first position in which it is fully closed and a second position in which it is fully open by means of one or more pneumatic piston-cylinder assemblies with counteracting first and second cylinder chambers are moved.

The piston-cylinder arrangements are designed and coupled to the lifting door in such a way that an enlargement of the first cylinder chambers, starting from the first position, causes a reduction in the second cylinder chambers and a displacement of the lifting door in the direction of the second position, and vice versa Enlargement of the second cylinder chambers, starting from the second position, causes a reduction in the size of the first cylinder chambers and a displacement of the lifting door in the direction of the first position.

The machine tool has a lifting door actuation device, with which the first and the second cylinder chambers for moving the lifting door from the first position to the second position and vice versa from the second position to the first position can be pressurized with compressed air in such a way that the first and the second cylinder chambers are pressurized with compressed air both when the lifting door is moved from the first position into the second position and when the lifting door is moved from the second position into the first position. Both the first cylinder chambers and the second cylinder chambers are thus subjected to compressed air both when opening and when closing the lifting door.

This results in the advantage that the lifting door is always clamped between the first and second cylinder chambers when moving between the fully closed position and the fully open position and can be opened and closed in a controlled manner.

Preferably, the effective piston areas of the first cylinder chambers and the second cylinder chambers are unequal, it being preferred that the effective piston area of the first cylinder chambers is smaller than the effective piston area of the second cylinder chambers.

The first and second cylinder chambers can be formed by separate single-acting pneumatic cylinders and/or by one or more double-acting pneumatic cylinders, which are preferably designed as differential cylinders. In particular, the use of differential cylinders has the advantage that a simple design with few components is possible.

The lifting door actuation device of the machine tool has a servopneumatic valve (proportional valve), in particular an electropneumatic pressure control valve, for pressurizing the second cylinder chambers with compressed air during the movement of the lifting door from the first position to the second position and from the second position to the first position. With such valves, the pressure in the second cylinder chambers can be adjusted to any desired pressure between atmospheric pressure and supply air pressure (system pressure) and the second cylinder chambers can preferably also be shut off. When using valves of this type, any pressure fluctuations in the compressed air network no longer have any effect on the function of the lifting doors and the speed of movement of the lifting door can be influenced.

Preferably, the machine tool is designed such that the lifting door is moved vertically upwards when moving from the first, fully closed position to the second, fully open position. This makes it possible in a simple manner to remove the lifting door completely from the machine operator's field of action.

It is also preferred that the machine tool is designed in such a way that the lifting door can be stopped in an intermediate position between the first position and the second position and temporarily clamped pneumatically via the first and second piston-cylinder assemblies, e.g. to carry out cleaning work at a viewing window of the lifting door.

It is also advantageous that the lifting door actuation device of the machine tool is designed in such a way that the speed of movement of the lifting door from the first position to the second position and/or from the second position to the first position can be adjusted by acting on the first cylinder chambers and second cylinder chambers with compressed air at specific pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Further preferred embodiments of the invention emerge from the dependent claims and from the following description with reference to FIG. 1. This shows the pneumatic diagram of a punching press according to the invention.

WAYS TO CARRY OUT THE INVENTION

1 shows the pneumatic diagram of a punching press according to the invention. As can be seen, the stamping press receives compressed air via a compressed air network 1 with a compressed air tank 3. The compressed air tank 3 is fed by a compressor 2 via a pressure reducing valve and is kept at a system pressure of 5.8 bar.

In addition to actuating devices 13a, 13b, not described in detail here, for the clutch 15a and the brake 15b of the combined clutch and brake unit 14 of the press drive, the punching press has actuating devices 4a, 4b for the front lifting door 8a and the rear lifting door 8b of the punching room protective covering.

As can be seen, the lifting doors 8a; 8b are respectively moved to open and close in the vertical direction between a first position B in which they are fully closed and a second position A in which they are fully open. This is done with two pneumatic differential cylinders with counteracting first 9a; 9b and second cylinder chambers 10a; 10b.

The differential cylinders are each designed in this way and with the lifting doors 8a; 8b coupled that an enlargement of the first cylinder chambers 9a; 9b, starting from the first position B of the lifting door, a reduction in size of the second cylinder chambers 10a; 10b and causes a displacement of the lifting door in the direction of the second position A and an enlargement of the second cylinder chambers 10a; 10b, starting from the second position A, a reduction in the size of the first cylinder chambers 9a; 9b and causes a displacement of the lifting door in the direction of the first position B.

With the lifting door actuators 4a; 4b are the first cylinder chambers 9a; 9b and the second cylinder chambers 10a; 10b for moving the respective lifting door 8a; 8b from the first position B to the second position A and from the second position A to the first position B can be pressurized with compressed air in such a way that the first cylinder chambers 9a; 9b and the second cylinder chambers 10a; 10b both when moving the respective lifting door 8a; 8b from the first position B to the second position A as well as when moving the lifting door 8a; 8b from the second position A to the first position B with compressed air.

To this end, the lifting door actuators 4a; 4b, in addition to the differential cylinders, a pulse-controlled first 3/2-way solenoid valve 5a, 5a, by means of which the first cylinder chambers 9a, 9b of the differential cylinders can optionally be opened via throttles and pilot-operated check valves 7a; 7b can be fed with compressed air from the compressed air network 1 or the line sections between the check valves 7a; 7b and the first solenoid valve 5a, 5a can be switched to atmosphere. The pressure in the line between the solenoid valve 5a, 5a and the check valves 7a; 7b is in each case via a pressure transmitter 6a; 6b monitored. To unlock the check valves 7a; 7b is a second 3/2-way solenoid valve 12a; 12b present, which the control lines of the check valves 7a; 7b switches to atmosphere in the de-energized state and pressurized with compressed air in the activated (energized) state. Next include the lift door actuators 4a; 4b each have an electropneumatic pressure control valve 11a, 11b, by means of which the second cylinder chambers 10a, 10b of the differential cylinder can be fed with compressed air from the compressed air network 1 at a certain pressure, can be switched to atmosphere or can also be blocked.

In the normal punching operation, the lifting doors 8a, 8b are braced in the lower, first position B. The lower, first cylinder chambers 9a, 9b are pressureless and the line sections between the check valves 7a; 7b and the first 3/2-way solenoid valves 5a, 5a are switched to atmosphere via these valves 5a, 5b. The upper, second cylinder chambers 10a, 10b are pressurized with compressed air at a pressure of about 5.6 bar via the respective electropneumatic pressure control valve 11a, 11b. The second 3/2-way solenoid valves 12a; 12b for unlocking the check valves 7a; 7b are de-energized, so that the control lines to the check valves 7a; 7b are pressureless and the check valves 7a; 7b are blocked.

If one of the lifting doors 8a, 8b is to be opened starting from this state, the first 3/2-way solenoid valve 5a, 5b of the respective lifting door actuating device 4a; 4b switched so that the lower, first cylinder chambers 9a; 9b can be pressurized with compressed air under system pressure (5.8 bar). The electropneumatic pressure control valve 11a, 11b of the lifting door actuator 4a; 4b lowers its working pressure from 5.6 bar to 1.5 bar and the lifting door 8a; 8b subsequently moves vertically upwards from the lower, fully closed position B until it has reached the upper, fully open position A.

Arrived in position A, the lifting door 8a, 8b is braced by the electropneumatic pressure control valve 11a, 11b of the lifting door actuating device 4a; 4b depressurizes the upper, second cylinder chambers 10a, 10b. The control lines of the check valves 7a; 7b are still pressureless, so that this valve 7a; 7b are blocked.

Starting from this situation, the lifting door 8a; 8b to close again, the control lines of the check valves 7a; 7b by controlling (energizing) the second 3/2-way solenoid valve 12a; 12b is pressurized with compressed air under system pressure (5.8 bar), so that the check valves 7a; 7b are unlocked. The electropneumatic pressure control valve 11a, 11b of the lifting door actuator 4a; 4b goes to a working pressure of 5.2 bar and the lifting door 8a; 8b subsequently moves vertically downwards from the upper, fully open position A until it has reached the lower, fully closed position B. The working pressure of the electropneumatic pressure control valve 11a, 11b (5.2 bar) was chosen so that the lifting door 8a; 8b is moved downwards with a holding force of less than or equal to 150 N.

Arrived in position B, the lifting door 8a, 8b is braced by the electropneumatic pressure control valve 11a, 11b of the lifting door actuating device 4a; 4b, the upper, second cylinder chambers 10a, 10b are pressurized with compressed air at a pressure of approx. 5.6 bar. The second 3/2-way solenoid valve 12a; 12b is de-energized so that the control lines to the check valves 7a; 7b are pressureless and the check valves 7a; 7b are blocked. The first 3/2-way solenoid valve 5a, 5b is then switched so that the line sections between the check valves 7a; 7b and the first 3/2-way solenoid valve 5a, 5a are switched to atmosphere via this valve 5a, 5b.

In order to clean the viewing window of the lifting doors, they must be placed in an intermediate position C between the lower, first position B and the upper, second position A. For this purpose, based on the situation just described, the first 3/2-way solenoid valve 5a, 5b of the respective lifting door actuation device 4a; 4b switched so that the lower, first cylinder chambers 9a; 9b can be pressurized with compressed air under system pressure (5.8 bar).

The electropneumatic pressure control valve 11a, 11b of the lifting door actuator 4a; 4b lowers its working pressure from 5.6 bar to 1.5 bar and the lifting door 8a; 8b subsequently moves vertically upwards from the lower, fully closed position B. Once the lifting door 8a; 8b has reached the intermediate position C, the electropneumatic pressure control valve 11a, 11b is de-energized and thereby blocked. The lifting door 8a; 8b is now clamped in the intermediate position C and can be cleaned.

If the cleaning work is finished, the electropneumatic pressure control valve 11a, 11b of the lifting door actuator 4a; 4b activated and set to a working pressure of 1.5 bar. The lifting door 8a; 8b subsequently moves vertically upwards from the intermediate position C until it has reached the upper, fully open position A.

Starting from this situation, the lift door 8a; 8b to close again, as already described above, the control lines of the check valves 7a; 7b by controlling (energizing) the second 3/2-way solenoid valve 12a; 12b is pressurized with compressed air under system pressure (5.8 bar), so that the check valves 7a; 7b are unlocked. The electropneumatic pressure control valve 11a, 11b of the lifting door actuator 4a; 4b goes to a working pressure of 5.2 bar and the lifting door 8a; 8b subsequently moves vertically downwards from the upper, fully open position A until it has reached the lower, fully closed position B.

While the present application describes preferred embodiments of the invention, it is to be understood that the invention is not limited thereto and may be otherwise embodied within the scope of the following claims.

Claims (19)

1. Method for actuating a lifting door (8a; 8b) in a machine tool, in particular in an automatic punching machine, wherein the lifting door (8a; 8b) for opening and closing in the vertical direction between a first position (B) in which the lifting door (8a; 8b) is fully closed and a second position (A) in which the lifting door (8a ; 8b) is completely open, is moved by means of one or more pneumatic piston-cylinder arrangements with first cylinder chambers (9a; 9b) and second cylinder chambers (10a; 10b) working in opposite directions, An enlargement of the first cylinder chambers (9a; 9b) starting from the first position (B) causes a reduction in the size of the second cylinder chambers (10a; 10b) and a displacement of the lifting door (8a; 8b) in the direction of the second position (A). and an enlargement of the second cylinder chambers (10a; 10b) starting from the second position (A) causes a reduction of the first cylinder chambers (9a; 9b) and a displacement of the lifting door (8a; 8b) in the direction of the first position (B). , and wherein the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a; 10b) both when the lifting door (8a; 8b) is moved from the first position (B) to the second position (A) and when the lifting door ( 8a; 8b) from the second position (A) to the first position (B) with compressed air. 2. The method according to claim 1, wherein the first cylinder chambers (9a; 9b) both when moving the lifting door (8a; 8b) from the first position (B) to the second position (A) and when moving the lifting door (8a; 8b ) from the second position (A) to the first position (B) are pressurized with compressed air at a first pressure (P1), while the second cylinder chambers (10a; 10b) move from the first position (8a; 8b) when the lifting door (8a; 8b) is moved B) in the second position (A) and/or when moving the lifting door (8a; 8b) from the second position (A) into the first position (B) with compressed air at pressures (P2, P3) which are different to the first print (P1). 3. The method according to claim 2, wherein the second cylinder chambers (10a; 10b) via a proportional valve (11a; 11b), in particular via an electropneumatic pressure control valve (11a; 11b) are acted upon with compressed air. 4. The method according to any one of claims 2 to 3, wherein the second cylinder chambers (10a; 10b) when moving the lifting door (8a; 8b) from the first position (B) to the second position (A) with compressed air at a second pressure ( P2), which is different from the first pressure (P1), and when the lifting door (8a; 8b) is moved from the second position (A) to the first position (B) with compressed air at a third pressure (P3). which is different from the first pressure (P1) and the second pressure (P2). 5. The method according to any one of the preceding claims, wherein the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a; 10b) are supplied with compressed air from a common compressed air source (3), which provides the compressed air at a system pressure (Ps). 6. The method according to any one of the preceding claims, wherein the lifting door (8a; 8b) is moved vertically upwards when moving from the first position (B) to the second position (A). 7. The method according to claims 4, 5 and 6, wherein the first pressure (P1) substantially corresponds to the system pressure (Ps) and the second pressure (P2) and the third pressure (P3) are lower than the system pressure (Ps). 8. The method according to any one of the preceding claims, wherein the lifting door (8a; 8b) in the first position (B) and / or in the second position (A) is braced pneumatically. 9. The method according to any one of the preceding claims, wherein when the lifting door (8a; 8b) is moved from the second position (A) to the first position (B), the pressures in the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a ; 10b) are selected such that the lifting door (8a; 8b) is closed with a specific closing force (Fs), in particular with a closing force (Fs) between 100N and 200N, in particular between 140N and 160N. 10. The method according to claim 9, wherein to determine the pressures which are required in the cylinder chambers (9a, 10a; 9b, 10b) to achieve the determined closing force (Fs) of the lifting door (8a; 8b), the pressures in the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a; 10b) when the lift gate (8a; 8b) is in an intermediate position (C) between the first position (B) and the second position (A) can be temporarily adjusted so that the lift gate (8a; 8b) is in limbo, and that then based on these pressures or pressure ratios and the known effective piston areas of the first cylinder chambers (9a; 9b) and second cylinder chambers (10a; 10b) the pressures are calculated at which the lifting door (8a; 8b) is closed with the specified closing force (Fs). 11. The method according to any one of the preceding claims, wherein when the lifting door (8a; 8b) is moved from the first position (B) to the second position (A), the pressures in the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a ; 10b) can be selected in such a way that the lifting door (8a; 8b) is opened at a certain speed. 12. The method according to any one of the preceding claims, wherein the lifting door (8a; 8b) is temporarily braced pneumatically in an intermediate position (C) between the first position (B) and the second position (A), in particular for carrying out cleaning work. 13. Machine tool, in particular an automatic stamping machine, with a lifting door (8a; 8b) which can be selectively opened or closed, in particular according to the method according to one of the preceding claims, for selectively making a machining area of the machine tool accessible or non-accessible, wherein the lifting door (8a; 8b) for opening and closing in the vertical direction between a first position (B) in which the lifting door (8a; 8b) is fully closed and a second position (A) in which the lifting door (8a ; 8b) is completely open, can be moved by means of one or more pneumatic piston-cylinder arrangements with first cylinder chambers (9a; 9b) and second cylinder chambers (10a; 10b) working in opposite directions, wherein the piston-cylinder arrangements are designed and coupled to the lifting door (8a; 8b) in such a way that an enlargement of the first cylinder chambers (9a; 9b) starting from the first position (B) results in a reduction of the second cylinder chambers (10a; 10b) and a Shifting the lifting door (8a; 8b) in the direction of the second position (A) and an enlargement of the second cylinder chambers (10a; 10b) starting from the second position (A) causes a reduction in the first cylinder chambers (9a; 9b) and a displacement of the lifting door (8a; 8b) in the direction of the first position (B), and wherein the machine tool has a lifting door actuating device (4a; 4b) with which the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a; 10b) for moving the lifting door (8a; 8b) from the first position (B) into the second position (A) and from the second position (A) into the first position (B) with compressed air, such that the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a; 10b) both during the process of the lifting door (8a; 8b) from the first position (B) to the second position (A) and when moving the lifting door (8a; 8b) from the second position (A) to the first position (B) with compressed air . 14. Machine tool according to claim 13, wherein the effective piston areas of the first cylinder chambers (9a; 9b) and the second cylinder chambers (10a; 10b) are unequal, in particular the effective piston area of the first cylinder chambers (9a; 9b) is smaller than the effective piston area of the second cylinder chambers (10a; 10b). 15. Machine tool according to one of claims 13 to 14, wherein the first cylinder chambers (9a; 9b) and second cylinder chambers (10a; 10b) are formed by separate single-acting pneumatic cylinders and/or are formed by one or more double-acting pneumatic cylinders, in particular by one or several differential cylinders. 16. Machine tool according to one of claims 13 to 15, wherein the lifting door actuating device (4a; 4b) has a proportional valve (11a; 11b), in particular an electropneumatic pressure control valve (11a; 11b), for pressurizing the second cylinder chambers (10a; 10b) with compressed air during the movement of the lifting door (8a; 8b) from the first position (B) to the second position (A) and from the second position (A) to the first position (B). 17. Machine tool according to one of claims 13 to 16, wherein the lifting door (8a; 8b) is moved vertically upwards when moving from the first position (B) to the second position (A). 18. Machine tool according to one of claims 13 to 17, wherein the lifting door actuating device (4a; 4b) is designed such that the lifting door (8a; 8b) in the first position (B) and/or in the second position (A) , And in particular in an intermediate position (C) between the first position (B) and the second position (A), can be clamped pneumatically via the first and second piston-cylinder assemblies. 19. Machine tool according to one of claims 13 to 18, wherein the lifting door actuating device (4a; 4b) is designed such that the speed of travel of the lifting door (8a; 8b) from the first position (B) to the second position (A) and /or can be adjusted from the second position (A) to the first position (B) by subjecting the first cylinder chambers (9a; 9b) and second cylinder chambers (10a; 10b) to compressed air at specific pressures.