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EP-3804903-B1 - CLAMP SYSTEM EQUIPPED WITH FUNCTION FOR DETECTING BEHAVIOR OF OBJECT TO BE CLAMPED

EP3804903B1EP 3804903 B1EP3804903 B1EP 3804903B1EP-3804903-B1

Inventors

  • AKAMATSU, HIROSHI

Dates

Publication Date
20260506
Application Date
20190725

Claims (3)

  1. A clamp system equipped with function for detecting behavior of object to be clamped, said clamp system provided for a machining center for mounting a clamped object (W), in which thickness of a gripped portion (WF) of the clamped object (W) varies, on a reference member (P, PZ) and processing the clamped object (W) after being clamped on the reference member (P, PZ) through an output member (12) by being pressed to the reference member (P, PZ), comprising: a clamp device (1) in which an overlapping distance between a coil (15) and the output member (12) made of a magnetic material is changed by stroke movement of the output member (12); a control unit (2) having a converter (23) for outputting a measured value of an inductance of the coil (15), and a memory (22) in which data indicating the measured value of the inductance of the coil (15) when the object to be clamped is clamped on the output member (12) in a process of moving the output member (12) from an unclamped state to a clamped state with respect to the clamped object (W) placed on the reference member (P, PZ) as the object to be processed is set as position of the output member (12) and a clamp area (E2) indicating a variation range allowed for the position is set; and a display unit (3) having an input/output function, on which various key tops are displayed, corresponding to numerical value input keys (32, 33), a key (34) for selecting an operation mode, keys (35, 36, 37) for determining clamp points including an empty clamp point (CLPM) indicating the position of the output member (12) in an empty clamp state, an unclamp point (UPCLM) indicating the position of the output member (12) in the unclamped state, and work clamp point (WCPM) indicating the position of the output member (12) that presses the clamped object (W), and a key (38) for setting the clamp area (E2) above and below the work clamp point (WCPM) and for setting margin ranges (E1, E3) starting from each of the unclamp point (UPCLM) and the empty clamp point (CLPM), wherein the control unit (2) is configured to report an execution of clamping to the controller of the machining center after setting the positions of the clamp area (E2) and the output member (12) in the memory (22), and to measure the inductance of the coil (15) during processing of the clamped object (W) by the machining center, to determine whether it is within a range of the clamp area (E2) stored in the memory (22), and to issue an abnormality to the controller of the machining center when the range is exceeded.
  2. The clamp system equipped with function for detecting behavior of object to be clamped according to claim 1, wherein the coil (15) is inserted into a bottomed hole (14) provided to the output member (12).
  3. The clamp system equipped with function for detecting behavior of object to be clamped according to claim 1, further comprising: a log memory (22g) for memorizing the measured value of the inductance of the coil (15) during processing as a log.

Description

FIELD OF THE INVENTION The present invention relates to a clamp system equipped with function for detecting behavior of object to be clamped. A machining center is provided with a clamp device for fixing a work to be clamped to a reference member such as a table or a pallet. As a clamp device, for example, a clamp device using a fluid pressure cylinder as disclosed in Patent Literature 1 is known. The work is grasped and released by a stroke movement of a piston of the fluid pressure cylinder. The clamp device driven by fluid pressure is equipped with a position detector to detect a stroke end. When the piston moves to the stroke end, the position of the stroke end is detected to stop supplying the pressure fluid. In the position detector of Patent Literature 1, a magnet is placed in the piston, and magnetic sensors for detecting magnetic force are placed in both ends of the stroke of the piston on the outside of the cylinder tube, respectively. When the piston reaches the stroke end, the magnetic sensor placed in the place detects the magnetic force of the magnet. Further, according to a position detector in Patent Literature 2, a clamp device is disclosed in which a piston made of a magnetic material is made hollow, a coil is inserted into the hollow, and a clamping device is arranged so that the overlapping distance with the coil changes according to the stroke movement of the piston. The piston position is detected by connecting a pulse from a fixed frequency pulse oscillator to the coil and then detecting the change in overlapping distance as a change in inductance. Compared with the technique of Patent Literature 1, there is no need to attach a magnetic sensor requiring an attachment place to a cylinder tube, and no attachment space is required to incorporate a magnet. WO 2005/009677 A1 discloses an automatic tool change device for exchanging tools in a spindle unit of a machine tool, in which a state of a tool clamped by a drawbar unit is checked by a main controller using an LC oscillating circuit. Some clamp devices are configured so as to detect the position of only one of the stroke ends. Such a device uses pressure fluid in moving toward one of the stroke ends, and utilizes elastic force of a spring in returning to the other stroke end. PRIOR ART PATENT LITERATURE Patent literature 1: Japanese Patent No. 3280345Patent literature 2: Japanese Patent Laid Open Publication No. 2003-156304 DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION The clamp device grasps the work on one side of the stroke ends and releases the work on the other side thereof. According to such a conventional technique, the position detector detects that the piston has reached the stroke end to be used to switch the stroke operation. In Patent Literature 2, the position detector detects an inductance change. This inductance change is converted into time or voltage and then compared with a predetermined threshold value, and when the predetermined position is reached, the switch output is generated assuming that the stroke end has been reached. The present invention provides a clamp system having a further enhanced function by detecting a behavior of an object to be clamped by using a stroke end position detector that has been used to detect that a piston has reached a predetermined position. MEANS TO SOLVE THE PROBLEM A clamp system equipped with a function for detecting a behavior of an object to be clamped according to the present invention is specified in claim 1. The clamp system includes a clamp device having an output member made of magnetic material which executes a stroke movement causing a change in an overlapping distance between the output member and a coil, a converter for outputting a measurement value of an inductance of the coil, a memory for setting a clamp area indicating a variation range permitted with respect to a position of the outputting member which is data representing the measurement value of the inductance of the coil when the object to be clamped is clamped on the output member, and a control unit measuring the inductance of the coil during processing of the clamped object, determining whether it is within a range of the clamp area stored in the memory, and issuing a signal which indicates an abnormality when the range is exceeded. EFFECTS OF INVENTION According to the present invention, it is possible to perform abnormality monitoring with respect to variations during processing for the clamp point by using the position detector for the stroke end, which has been used to detect that the piston has reached a predetermined position. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a machining center and a clamp system equipped with a function for detecting a behavior of an object to be clamped.FIGS. 2A to 2D show an example of a clamp device used in the clamp system, FIGS. 2A to 2B show a clamp device of a type having a swing arm, and FIGS. 2C to 2D show a clamp device of a type having a