Determination of the condition of chucks

Abstract

A method is provided for determining a state of a chuck (12) of a machine tool (1), the method comprising the steps: Moving at least one clamping jaw (122) of the chuck (12) according to a predetermined movement plan; measuring, over the period of the movement, a position of the clamping jaw (122); measuring, over the period of the movement, a force applied to move the clamping jaw (122); and comparing the recorded measured values ​​with respective predetermined reference values ​​to determine the condition of the chuck (12). Furthermore, a chuck (12) and a computer program product are provided, which are configured to carry out the method.

Description

Field of the invention

[0001] The present invention relates to the field of machine tools, and in particular to the field of laser processing machines for machining tubular or rod-shaped workpieces. More specifically, the present invention relates to the determination of a state of a chuck by means of which the tubular or rod-shaped workpieces can be clamped and guided (in particular, rotated and / or axially displaced) for machining in the machine tool. State of the art

[0002] Machine tools for machining tubular or rod-shaped workpieces, in which the workpieces are fixed by means of a chuck and are movable relative to a tool of a machine tool, are known from the prior art. For example, in connection with EP 2 548 691 B1, a laser processing machine known as "TruLaser Tube" from the applicant is described, which is schematically shown in Fig. 1. The laser processing machine 1 is designed for cutting tubular or rod-shaped workpieces 2 with any cross-sectional shape. The laser processing machine 1 comprises a feed device 3, by means of which the workpieces 3 are fed to a processing device 4 of the laser cutting machine 1. Via an unloading device 5, the workpieces 2 processed in the processing device 4 are removed for further use and, if necessary, collected for further transport. All essential functions of the laser processing machine 1 are controlled by a numerical control device 6.

[0003] The feeding device 3 comprises a rotating and feed device 7 serving as a workpiece movement device, as well as a machine bed 8 with guide rails 9 and a push-through device 10. The rotating and feed device 7 is motor-driven and can be moved in the feed direction 11 on the guide rails 9. On the side facing a workpiece 2 to be fed, the rotating and feed device 7 has a chuck 12 which can be rotated in the direction of the double arrow 13 and which grips the fed workpiece 2 from the outside and / or from the inside (in the case of larger hollow profiles or open profiles) and clamps it in place. Fig. 2a and Fig.2b shows exemplary chucks 12 for a laser processing machine 1, each having at least two clamping jaws 122, wherein the clamping jaws 122 are arranged at equal intervals along the circumferential direction of a base body 120 of the chuck 12 and are mounted so as to be movable in the radial direction with respect to the base body 120.

[0004] The fed workpiece 2 is supported by at least one workpiece support 14 integrated into the machine bed 8. In the area of ​​the machining device 4, the workpiece 2 is guided through the push-through device 10. The push-through device 10 is designed such that the clamped workpiece 2 is guided in the feed direction 11 and is not clamped in a fixed position. The workpiece 2 is rotatable in the push-through device 10 about the rotation axis 13.

[0005] The processing device 4 comprises a laser beam source 15 for generating a laser beam 16, a processing head 17, and a beam guide 18 that guides the laser beam 16 from the laser beam source 15 to the processing head 17. The laser beam 16 exits the processing head 17 and is focused onto the outer peripheral surface of the clamped workpiece 2 at a processing point F. On the side of the feed-through device 10 facing away from the machine bed 8, the unloading device 5 is provided, which removes the processed (in particular, cut) workpieces 2 from the laser processing machine 1.

[0006] In order to increase the productivity of the laser processing machine 1, a loading device 19 can be provided as an automation component, with which a workpiece 2 is automatically transported to a transfer position and transferred to the feeding device 3 of the laser processing machine 1.

[0007] The chuck 12 of the feed device 3 is subjected to heavy loads during operation of the laser processing machine 1 and can become stiff over time due to contamination or wear. This stiffness can lead to a decrease in the clamping force of the clamping jaws, and workpieces 2 can no longer be reliably held and guided, which can lead to collisions between workpieces 2 and machine components and / or the failure of the laser processing machine 1.

[0008] The present invention is based on the object of detecting a critical stiffness of chucks in order to be able to take suitable preventive measures (e.g. cleaning or replacing a chuck) in good time. The invention

[0009] The problem underlying the invention is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0010] According to a first aspect of the invention, a method is provided for determining the state of a chuck of a machine tool. The machine tool can be, for example, a laser processing machine for processing, in particular for cutting and / or welding, elongated components, in particular pipes or profiles made of metal or another material. In this case, the state refers to a functional state of the chuck, which particularly includes the movability of the chuck, taking into account the force required for the movements of the chuck—and in particular its clamping jaws.

[0011] The method comprises moving at least one clamping jaw of the chuck according to a predetermined movement plan. The movement plan can, in particular, specify a movement path, i.e., a distance to be covered by the respective clamping jaw (e.g., the distance from a radially innermost position to a radially outermost position of the clamping jaw), and a speed for the movement of the respective clamping jaw. To carry out a measuring cycle, it can be advantageous if several, in particular all, clamping jaws of the chuck are moved simultaneously. A typical chuck of a machine tool can, for example, have two, three, or four clamping jaws.A movement plan of a clamping jaw for determining the state of the chuck can preferably specify a movement or a movement sequence of the at least one clamping jaw that is specifically intended for determining a state of the chuck and that is not suitable for clamping a workpiece - for example, a single or repeated outward movement and / or inward movement of the clamping jaw, possibly at different speeds and / or with intermediate movement stops. The force provided for moving the clamping jaws can also be set lower than that required for actually clamping a workpiece. In the case of a pneumatically operated chuck, for example, pressures of less than 10 bar, preferably less than 5 bar, for example approximately 2 bar, can be used.By reducing the force required to move the clamping jaws, stiffness in the chuck can be detected earlier and more clearly.

[0012] The method further comprises measuring, over the period of movement, a position of the respective clamping jaw and a force applied to move the clamping jaw.

[0013] The movement of at least one clamping jaw according to the movement plan and the simultaneous measurement of the measured values ​​desired to determine the state can be referred to jointly as a measuring cycle.

[0014] Finally, the method includes comparing the recorded measured values ​​with respective specified reference values ​​to determine the condition of the chuck.

[0015] According to a preferred variant, the chuck is a pneumatically driven chuck. In this case, measuring the force can comprise measuring a pressure in a cylinder chamber of at least one pneumatic cylinder that is used to move the clamping jaw or several of the clamping jaws. Furthermore, in this case a measuring cycle can additionally comprise measuring a respective position (i.e. in particular "open" or "closed") of those pneumatic valves that control the pressure in the respective cylinder chamber. Preferably, several pneumatic cylinders are used to move the clamping jaws and, during a measuring cycle, the respective position of all valves of the pneumatic system involved in controlling the movement is recorded over time.

[0016] It is understood that the drive of a clamping jaw of the chuck can also be carried out, for example, by means of a hydraulic system and / or electrically.

[0017] The method may further comprise outputting an indication indicating stiffness of the chuck if, based on the comparison of the measured values ​​with the reference values, it is determined that an actual movement speed of the clamping jaw falls below a predetermined reference speed by at least a predetermined, critical amount. The movement speed may refer to the average speed over the period of movement, or else the speed at a specific point in time or a maximum speed during the movement of a respective clamping jaw. An indication may also be output if a change in speed, in particular the movement acceleration, lasts at least a critical amount longer than a predetermined value.

[0018] The indication may preferably be given visually on the screen of an operator terminal of the machine tool and / or by means of a light signal from a warning lamp on the machine tool and / or acoustically.

[0019] A warning may also be issued if, based on the comparison of the measured values ​​with the reference values, it is determined that a delay between the activation of a movement of the clamping jaw and the actual start of movement exceeds a predetermined, acceptable delay by at least a predetermined, critical amount.

[0020] According to a preferred variant, it can be provided that several movements of the respective clamping jaw are carried out consecutively, each following its own movement plan. Furthermore, the movement plans of two consecutive movements can preferably differ in the specified movement distance and / or in the specified movement speed. For example, all clamping jaws can be moved back and forth simultaneously from the radially innermost position to the radially outermost position of the clamping jaws according to a first movement plan at a first speed. Subsequently, the clamping jaws can be moved over the same distance according to a second movement plan, but at a second, faster speed.According to a third movement plan, the clamping jaws can then be moved, for example, from the radially innermost to the radially outermost position at a third speed, with the movement being stopped abruptly halfway and continued after a dwell time of, for example, less than one second.

[0021] It can also be provided that the condition check of the chuck according to the invention is carried out automatically after a predetermined in-operation time of the machine tool has elapsed.

[0022] According to a further aspect of the invention, a chuck for clamping a workpiece is provided. The chuck comprises at least two clamping jaws and at least one pneumatic cylinder for moving at least one of the clamping jaws. The chuck further comprises a pressure control system with a plurality of valves and sensors, as well as at least one pressure regulator, for respectively detecting and adjusting a pressure in the cylinder chambers of the pneumatic cylinder. The chuck comprises at least one displacement sensor for detecting a position of at least one of the clamping jaws. Finally, the chuck comprises a control unit, which is connected to the pressure regulator for control purposes in order to control a movement of the at least one clamping jaw. The control unit is further configured to control the chuck for carrying out a method according to one of the variants described above in order to determine a state of the chuck.

[0023] According to a further aspect, a computer program product is provided which contains computer-readable information for carrying out a method according to one of the variants described above and which is configured to be read out by the control unit of a chuck as described above. Example

[0024] To test its effectiveness, the method according to the invention was carried out on a tube laser cutting machine. The laser cutting machine featured a conventional pneumatic chuck with four clamping jaws. The key components and the operating principle of such a chuck are briefly described below. • The pneumatic chuck drive comprises several pneumatic cylinders whose movements are translated by mechanical gear components and transmitted to the clamping jaws. Each cylinder has a first cylinder chamber and a second cylinder chamber. If the pressure in the first chamber is greater than in the second chamber, a cylinder piston of the respective cylinder is moved in a first direction, and vice versa. The movement of the cylinder piston stimulates the movement of the associated clamping jaws. By increasing the pressure difference in the cylinder chambers, the clamping force of the chuck can be increased. • The chuck drive is equipped with one or more automatic pressure regulators. These pressure regulators allow the laser cutting machine's control system to automatically adjust the pressure in the cylinder chambers based on the desired clamping force. The pressure regulators also record the actual pressures achieved in the cylinder chambers and transmit them to the machine control system. • The chuck drive also features several pneumatic valves. These valves allow the machine control system to start or stop the cylinder chambers from being pressurized with a specified air pressure.

[0025] The chuck used was equipped with several sensors to detect the respective position of the clamping jaws. In normal production, these sensors are used to detect the workpiece. If necessary, they can also detect an incorrect workpiece or a workpiece that has fallen out.

[0026] To apply the method according to the invention, the control system was programmed to perform predefined measuring cycles at regular intervals. For each measuring cycle, different pressures were specified for each cylinder chamber (e.g., in the range of a few bars (e.g., 2 bar)) to execute movements of the clamping jaws according to predefined movement plans. In some measuring cycles, the movement was also interrupted midway through. During the movements of the clamping jaws, the following information from the chuck was recorded over time using the existing sensors: • Position of the clamping jaws (from the position measuring sensors); • Target pressure and actual pressure in the cylinder chambers of the pneumatic cylinders (from the pressure regulators); and • Valve positions.

[0027] The recordings were then evaluated. For example, slowed movement of the clamping jaws was identified as an indication of a dirty, stiff chuck. However, there are also other indicators, such as an extended time between the activation of a valve and the actual movement of a clamping jaw associated with the valve. To identify any anomalies, the recordings were compared with older recordings from the same machine. However, recordings from identical machines can also be used as a reference.

[0028] The laser processing machine on which the method according to the invention was carried out operated during normal operation using a release agent inside the pipe, which caused the chuck to become contaminated relatively quickly during operation. After just two weeks of operation, a significant stiffness of the chuck was detected in a timely manner due to changes in the measurement curves during the measurement cycles. This was remedied by cleaning the chuck. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 2 548 691 B1

[0002]

Claims

[1] Method for determining the state of a chuck (12) of a machine tool (1), the method comprising the steps: Moving at least one jaw (122) of the chuck (12) according to a predetermined motion plan; Measure, over the period of movement, a position of the clamping jaw (122); Measure, over the period of movement, a force applied to move the clamping jaw (122); Comparing the recorded measured values ​​with respective predefined reference values ​​to determine the condition of the chuck (12). [2] Method according to claim 1, wherein the movement of the chuck (12) is pneumatically driven; wherein measuring the force comprises measuring a pressure in a cylinder chamber of at least one pneumatic cylinder used to move the clamping jaw (122); and wherein the method further comprises: Measuring, over the period of movement, a respective position of those pneumatic valves that control the pressure in the cylinder chamber. [3] Method according to one of the preceding claims, further comprising issuing a warning indicating stiffness of the chuck (12) when, on the basis of comparing the measured values ​​with the reference values, it is determined that an actual movement speed of the jaw (122) falls below a predetermined reference speed by at least a predetermined critical amount. [4] Method according to one of the preceding claims, further comprising issuing a warning indicating stiffness of the chuck (12) when, based on a comparison of the measured values ​​with the reference values, it is determined that a delay between the control of a movement of the clamping jaw (122) and the actual start of the movement exceeds a predetermined acceptable delay by at least a predetermined critical amount. [5] Method according to one of the preceding claims, wherein several movements of the clamping jaw (122) are performed successively, each following its own movement plan. [6] Method according to claim 5, wherein the motion plans of two successive movements differ in the predetermined motion distance and / or in the predetermined motion speed. [7] Chuck (12) for clamping a workpiece, the chuck (12) comprising: At least two clamping jaws (122); At least one pneumatic cylinder for moving at least one of the clamping jaws (122); A pressure control system comprising a plurality of valves and sensors, as well as at least one pressure regulator, for the respective detection and adjustment of a pressure in the cylinder chambers of the pneumatic cylinder; At least one displacement sensor to detect the position of at least one of the clamping jaws (122); A control unit which is connected to the pressure regulator in a control-technical manner in order to control a movement of the at least one clamping jaw (122), and which is further configured to control the chuck (12) to carry out a method according to one of the preceding claims in order to determine a state of the chuck (12). [8] Computer program product containing computer-readable information for carrying out a method according to any one of claims 1 to 6 and which is set up for reading by the control unit of a chuck (12) according to claim 7.

Images