JP2008012588A - Working machine and control method for working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method for a working machine such as a press by which when a working tool approaches a workpiece, position control is performed and when power control is performed after the working tool contacts the workpiece, impact force produced upon the contact of the working tool with the workpiece is suppressed and the accuracy of the power control is improved. <P>SOLUTION: During the period of time that the working tool (such as a movable die) 18 approaches the workpiece 28, position control is performed, and the position of the tool 18 is controlled to a position object. Further, the strain of a structural part 26 as the frame of the working machine 10 is detected, and the detected strain is compared with a prescribed threshold. The threshold is set to the value slightly higher than the value of the strain detected when the working tool 18 and the workpiece 28 are not contacted. Since the moment the working tool 18 contacts the workpiece 18 the value of the detected strain reaches the threshold, an automatic change from position control to power control is immediately performed, and on and after, the power applied to the workpiece 28 is controlled to a prescribed power object. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a processing machine such as a press machine, a bending machine, an extrusion machine, and an injection molding machine, and a control method thereof.

  In a forging machine such as an electric servo press machine, position control for controlling the speed of the movable mold according to the position deviation between the detected value of the position of the movable mold and the position command, and the movable mold A control device configured to selectively execute a pressure control for controlling the speed of the movable mold in accordance with a pressure deviation between a detected value of pressure applied to the workpiece from the pressure command and a pressure command. This is disclosed in Japanese Unexamined Patent Publication No. 2006-7296 (Patent Document 1). The controller calculates the speed command based on the position deviation at the same time to determine whether position control or pressure control should be selected, and also calculates the speed command based on the pressure deviation, and both speeds Compare the commands and select the smaller speed command. Therefore, when the movable die approaches the workpiece, the position control is selected because the speed command based on the position deviation is smaller than that based on the pressure deviation. After that, when the movable mold comes into contact with the workpiece, the speed of the movable mold decreases and the speed command based on the position deviation increases, while the pressure applied to the workpiece rises to the pressure deviation. The speed command based on it is lowered. When both speed commands coincide and the magnitude relationship between the two is reversed, switching from position control to pressure control is performed, and thereafter, while the movable die presses the workpiece, the pressure is Control will be executed.

JP 2006-7296 A

  Patent Document 1 describes that the transition from the position control to the pressure control is continuously and smoothly performed by comparing the speed commands of the position control and the pressure control and selecting the smaller one. . However, in practice, according to this method, the pressure applied to the workpiece increases after the movable mold comes into contact with the workpiece, and the moving speed of the movable mold decreases, and the speed of pressure control and position control is reduced. Switching from position control to pressure control does not occur until the magnitude relationship between the commands is reversed. Therefore, there is a problem that when the movable mold comes into contact with the workpiece, a short-time collision phenomenon occurs and a large impact force is applied to the workpiece.

  Further, in order to perform pressure control (force control for controlling the processing force in a broad sense), it is necessary to accurately detect the pressure or processing force applied to the workpiece from the mold. However, in the conventional method of detecting the shaft torque of a servo motor, which is a power source, accurate pressure or machining force is affected by the viscous resistance force and friction force of the mechanism and the change of motor characteristics. There is also a problem that it is difficult to detect.

  Such a problem may exist not only in a forging machine such as the electric servo press machine disclosed in Patent Document 1, but also in other types of processing machines.

  Accordingly, an object of the present invention is to suppress an impact force when a processing tool such as a movable mold comes into contact with a workpiece in a processing machine that selectively executes position control and force control.

  Another object of the present invention is to improve the accuracy of force control.

  A processing machine according to the present invention includes a power source, a mechanism portion that receives power from the power source and moves to apply force to the workpiece, a structure portion that supports the mechanism portion and the workpiece, and a controller that controls the power source. With. The controller detects a force applied to the workpiece from the mechanism unit, a force control unit for generating a first control command based on a force feedback value from the force detection unit, and a position of the mechanism unit Position detection means, position control means for generating a second control command based on a position feedback value from the position detection means, one of the first control command and the second control command is selected, and the selected control command And automatic selection means for controlling the power source on the basis thereof. The automatic selection means selects the second control command from the position control means while the mechanism portion is approaching the workpiece, compares the force feedback value from the force detection means with a predetermined threshold value, and compares the result. If the force feedback value is smaller than the threshold value, the second control command is still selected, but if the force feedback value is equal to or greater than the threshold value, the first control command from the force control means is selected.

  According to this processing machine, position control is executed while the mechanism portion is approaching the workpiece. Thereafter, when the mechanical unit comes into contact with the workpiece, the force feedback value rises and reaches a threshold value, and switching from position control to force control is performed at the moment of this arrival. By appropriately setting the threshold value, the mechanism unit shifts from position control to force control at the moment when the mechanism unit contacts the workpiece, thereby reducing the impact force caused by the collision between the mechanism unit and the workpiece. it can.

  According to a preferred embodiment, the force control means is configured to perform control so that the force feedback value approaches a predetermined force target value. The threshold value is set lower than the force target value. As a result, when the mechanism portion comes into contact with the workpiece, it is possible to shift from position control to force control earlier than the force feedback value reaches the force target value. Thereby, the impact force caused by the collision between the mechanism portion and the workpiece can be further reduced.

  According to a preferred embodiment, the threshold value is set larger than the force feedback value at the time of non-contact in the vicinity of the force feedback value at the time of non-contact between the mechanism portion and the workpiece. As a result, the position control is shifted to the force control at the moment when the mechanism portion comes into contact with the workpiece, whereby the impact force caused by the collision between the mechanism portion and the workpiece can be further reduced.

  In a preferred embodiment, the force detection means detects a strain generated in the structure portion, and detects a force applied to the workpiece from the strain. The strain generated in the structure part is substantially proportional to the force applied to the workpiece, and is substantially unaffected by changes in the viscous resistance force and frictional force of the mechanism part and motor characteristics. Therefore, the accuracy of force control is improved by detecting the force applied to the workpiece based on the strain generated in the structure portion.

  According to the present invention, in a processing machine that selectively executes position control and force control, an impact force when a processing tool such as a movable mold comes into contact with a workpiece can be suppressed.

  In addition, in order to detect the force applied to the workpiece from the mechanism portion, when the reaction force generated in the structure portion is detected according to the force, the accuracy of force control can be improved.

  Embodiments of the present invention will be described below. Although the present invention can be applied to various processing machines, an embodiment in which the present invention is applied to an electric servo motor as a power source will be described below as an example.

  FIG. 1 shows a schematic structure of an electric servo press according to the present embodiment.

  As shown in FIG. 1, this press machine 10 has an electric servo motor 12 as a power source, and this servo motor 12 is controlled by a controller (not shown in FIG. 1, see FIG. 2). The servo motor 12 may be a rotary motor or a linear motor. When the servo motor 12 is a rotary motor, the rotary shaft of the servo motor 12 is connected to a slide shaft 16 via a motion conversion mechanism (for example, a ball screw, a crank slider, a link mechanism, etc.) 14 that converts a rotary motion into a linear motion. Combined with On the other hand, when the servo motor 12 is a linear motor, the linear motion shaft of the servo motor 12 may be directly coupled to the slide shaft 16. A slide 18 is coupled to the slide shaft 16, and a movable mold 20 is attached to the slide 18. The motion conversion mechanism 14, the slide shaft 16, the slide 18, and the movable mold 20 are mechanisms that move with power from a power source. Further, the fixed mold 22 is disposed so as to face the movable mold 20. The mechanism portion 24 and the fixed mold 22 are supported by the framework, that is, the structure portion 26 of the press 10. The workpiece 28 is set between the movable mold 20 and the fixed mold 22 and is pressed by the movement of the movable mold 20.

  The press machine 10 is further provided with a position detector 30 and a strain detector 32. The position detector 30 is attached to the slide 18 and the structure unit 26, for example, and detects the position of the mechanism unit 24 in the movement direction, for example, the position of the slide 18 in the linear movement direction. Further, the strain detector 32 is, for example, a strain gauge or a load cell attached to the structure unit 26, and the magnitude of the strain of the structure unit 26, in other words, by a controller (not shown in FIG. 1) based on the output signal. Then, the magnitude of the machining force output from the mechanism unit 24 can be measured. Further, although not shown in FIG. 1, a speed detector for detecting the speed of the servo motor 12 is also provided (see FIG. 2). As will be described later, the controller uses the position of the mechanism unit 24 detected by the position detector 30 as a feedback value to control the speed of the servo motor 12, thereby controlling the position of the mechanism unit 24 (hereinafter referred to as "position"). Control). Further, the controller controls the speed of the servo motor 12 using the distortion of the structure portion 26 detected using the strain detector 32, in other words, the machining force output from the mechanism portion 24 as a feedback value. Thus, the machining force is controlled (hereinafter referred to as “force control”).

  Here, it should be noted that in the force control, the strain of the structure portion 26 is detected in order to measure the processing force. Thereby, the control of the processing force with high accuracy can be realized. That is, the mechanism unit 24 receives a torque generated by the servo motor 12 and applies a processing force (compression force) to the workpiece 28. At this time, the reaction force against the machining force is transmitted to the structure portion 26, and the entire force line (the force transmission is indicated by an arrow) forms a closed loop as indicated by the arrow in FIG. There is no escape from the part 26. Therefore, the strain of the structure portion 26 is almost proportional to the processing force, so that the processing force can be obtained with high accuracy by measuring the strain of the structure portion 26. By performing force control using the obtained machining force as a feedback value, highly accurate machining force control is realized. Incidentally, a method of detecting a strain by attaching a strain gauge to the mechanism unit 24 (for example, the motor shaft, the slide shaft 16 or the slide 18) instead of the structure unit 26 may be used. However, the strain of the structure unit 26 is detected. Better. The reason is that it is difficult to accurately measure the processing force by the method of detecting the distortion of the mechanism portion 24. In general, the mechanism portion 24 is higher in rigidity than the structure portion 26 and is caused by a small amount of strain under the same force. Further, it is difficult to incorporate the load cell into the mechanism unit 24 such as the motor shaft or the slide shaft 16. Furthermore, in the method of detecting the torque of the motor shaft, not the strain, in order to measure the machining force, the accurate machining force is affected by the viscous resistance force and frictional force of the mechanism unit 24 and the change in motor characteristics. Is difficult to control.

  FIG. 2 shows a functional configuration of the controller of the press 10 described above.

  As shown in FIG. 2, the controller 50 includes a target setting device 52 and a calculation device 54. The target setting device 52 includes a force target setting unit 60 and a position target setting unit 62. The force target setting unit 60 outputs a target value (hereinafter referred to as “force target value”) for the machining force to the arithmetic device 54. The position target setting unit 62 outputs a target value (hereinafter referred to as “position target value”) regarding the position of the mechanism unit 24 to the arithmetic device 54.

  Not only the position detector 30 and the strain detector 32 shown in FIG. 1 but also a force calculator 56 and a velocity detector 58 not shown in FIG. 1 are associated with the controller 50. The force calculator 56 receives the output signal of the strain detector 32, calculates a value corresponding to the machining force, and outputs the value to the arithmetic unit 54. The speed detector 58 detects the speed of the servo motor 12 (in other words, the movement speed of the mechanism unit 24), and outputs the value of the speed to the arithmetic unit 54. Further, the position detector 30 detects the position of the mechanism unit 24 as described above, and outputs the position value to the arithmetic unit 54. Hereinafter, the machining force, speed, and position values input to the computing device 54 are referred to as “force feedback value”, “speed feedback value”, and “position feedback value”, respectively.

  As can be seen from the configuration of the arithmetic unit 54, the controller 50 has two main feedback control loops. One is a “force loop” for performing force control using a force feedback value, and the other is a “position loop” for performing position control using a position feedback value. One of the two loops is automatically selected by the automatic switching operation by the automatic switch 72.

  The force loop has a subtractor 64 and a force control unit 66. The subtractor 64 inputs a force target value from the force target setting unit 60 and inputs a force feedback value from the force calculator 56, and a deviation between the force target value and the force feedback value (hereinafter referred to as “force deviation”). Calculate The force control unit 66 inputs a force deviation from the subtracter 68, performs a predetermined calculation (for example, PID calculation) on the force deviation, and sets the speed deviation of the servo motor 12 to bring the force deviation close to zero. A first speed command that is a target value is generated. On the other hand, the position loop includes a subtracter 68 and a position control unit 70. The subtracter 68 receives a position target value from the position target setting unit 62 and a position feedback value from the position detector 30, and a deviation between the position target value and the position feedback value (hereinafter referred to as “position deviation”). Calculate The position control unit 70 receives a position deviation from the subtractor 68, performs a predetermined calculation (for example, PID calculation) on the position deviation, and sets a target value for the speed of the servo motor 12 to bring the position deviation close to zero. A second speed command is generated.

  The force loop and the position loop share the automatic switch 72, the subtracter 74, the speed controller 76, and the current controller 78. The automatic switch 72 receives the first speed command and the second speed command, selects one of them, and outputs the selected speed command (hereinafter referred to as “selected speed command”) to the subtracter 74. As one of judgment materials for this selection, the automatic switch 72 inputs a force feedback value. The automatic changer 72 initially selects the second speed command (that is, the position control is enabled and the force control is disabled) in one press working process, and at that time, the force feedback value and The threshold value preset in the automatic switch 72 is compared. As a result of this comparison, initially, the force feedback value is lower than the threshold value (ie, before the movable mold 20 contacts the workpiece 28). At this time, the automatic switch 72 continues to select the second speed command. When the slide 18 descends and the movable mold 20 contacts the workpiece 28, the force feedback value increases and exceeds the threshold value. At this time, the automatic switch 72 switches the selection from the second to the first speed command (that is, switches the control mode from position control to force control).

  The subtracter 74 calculates a deviation (hereinafter referred to as a speed deviation) between the selected speed command from the automatic switch 72 and the speed feedback value from the speed detector 58. The speed control unit 76 inputs a speed deviation, performs a predetermined calculation (for example, PID calculation) on the speed deviation, and is a target value for the excitation current of the servo motor 12 to bring the speed deviation close to zero. Generate a current command. The current control unit 78 inputs a current command from the speed control unit 76 and controls the excitation current of the servo motor 12 according to the current command, thereby bringing the speed of the servo motor 12 closer to the speed command.

  FIG. 3 shows the overall flow of operation and control of the press 10. FIG. 4 shows control logic for switching from position control to force control when the operation in FIG. 3 shifts from lowering to compression.

  As shown in FIG. 3, the pressing process of the press machine 10 includes the following five sub-processes, namely “stationary” in which the slide 18 is stopped at the top dead center, and the slide 18 is lowered. “Descent” approaching the workpiece 28 while the movable mold 20 comes into contact with the workpiece 28, “compression” compressing the workpiece 28 with the movable mold 20 and the fixed mold 22, and the movable mold 20. “Separation” in which the slide 18 ascends after being separated from the workpiece 28 and “stationary” in which the slide 18 stops at the top dead center are successively executed in this order.

  In this press working step, in the initial “still” and “down” sub-steps, the position control (that is, the second speed command) is selected by the automatic switch 72 as the control mode. As shown in FIG. 3, the position target value is constant at the top dead center when “still”, and decreases when “down”, and the position feedback value also changes along with this position target value. In this way, during the initial position control, the automatic switch 72 constantly compares the force feedback value with a predetermined threshold as shown in FIG. Here, the threshold value is set to a value smaller than the force target value (the machining force to be applied to the workpiece 28 in the “compression” sub-process). That is, the threshold value is a force feedback value in the vicinity of a force feedback value (substantially zero) in a state where the movable mold 20 is not in contact with the workpiece 28 in the substeps of “still” and “down”. It is set to a slightly larger value. As a result of the comparison, as long as the force feedback value is smaller than the threshold value, the position control (that is, the second speed command) is still selected. However, as a result of the above comparison, when the force feedback value becomes equal to or greater than the threshold value, the control mode is switched from position control to force control (that is, the selected speed command is changed from the second speed command to the first speed command). Is switched to).

  Therefore, position control is executed while the movable mold 20 is not yet in contact with the workpiece 28 in the sub-steps “stationary” and “down”. Thereafter, when the movable mold 20 comes into contact with the workpiece 28, the force feedback value rises and reaches the above threshold value. When this threshold value is reached, switching from the position control to the force control is performed. Is started. As described above, as soon as the movable mold 20 comes into contact with the workpiece 28, the position control is switched to the force control at an early stage. The impact force due to the collision with the object 28 is further suppressed. In order to reduce the impact force, it is desirable that the threshold value be set as small as possible within a range in which switching malfunction due to signal noise or the like does not occur. Therefore, in the present embodiment, as described above, the threshold value is set to a value slightly higher than that near zero.

  While the control mode shifts to force control and the “compression” sub-process is executed, the force feedback value is controlled to the force target value. Thereafter, for example, when a preset compression time elapses, the control mode is switched again from the force control to the position control by the automatic switch 72, whereby the "lifting" and "resting" sub-steps are performed. become.

  As mentioned above, although embodiment of this invention was described, this embodiment is only the illustration for description of this invention, and is not the meaning which limits the scope of the present invention only to this embodiment. The present invention can be implemented in various other modes without departing from the gist thereof.

1 is a schematic front view of a processing machine (electric servo press machine) according to an embodiment of the present invention. The block diagram which shows the function structure of the controller of the press machine. A time chart showing the overall flow of operation and control of the press. The time chart explaining the logic of the control which switches from position control to force control at the time of the operation mode of the press machine shifting from descent to compression.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electric servo press machine 12 Electric servo motor 14 Motion conversion mechanism 16 Slide shaft 16 Slide shaft 18 Slide 20 Movable mold 22 Fixed mold 24 Mechanism part 26 Structure part 28 Workpiece 30 Position detector 32 Strain detector 50 Controller 52 Target setting unit 54 Arithmetic unit 56 Force calculator 58 Speed detector 60 Force target setting unit 62 Position target setting unit 64 Subtractor 66 Force control unit 68 Subtractor 70 Position control unit 72 Automatic switch 74 Subtractor 76 Speed control unit 78 Current controller

Claims (5)

A power source (12); a mechanism portion (24) that receives power from the power source and moves to apply force to the workpiece (28); and a mechanism portion (26) that supports the mechanism portion and the workpiece. And a processing machine (10) comprising a controller (50) for controlling the power source,
The controller (50)
Force detection means (32, 56) for detecting a force applied to the workpiece from the mechanism portion;
Force control means (64, 66) for generating a first control command based on a force feedback value from the force detection means;
Position detecting means (30) for detecting the position of the mechanism unit;
Position control means (68, 70) for generating a second control command based on a position feedback value from the position detection means;
Automatic selection means (72 to 78) for selecting one of the first control command and the second control command and controlling the power source based on the selected control command;
The automatic selection means (72 to 78) selects the second control command from the position control means while the mechanism is approaching the workpiece, and a force feedback value from the force detection means. When the force feedback value is smaller than the threshold value as a result of the comparison, the second control command is still selected, and as a result of the comparison, the force feedback value is equal to or greater than the threshold value. If so, select the first control command from the force control means,
A processing machine characterized by that. The processing machine (10) according to claim 1,
The force control means (64, 66) generates the first control command so as to bring the force feedback value close to a predetermined force target value;
The processing machine, wherein the threshold is set lower than the force target value. In the processing machine according to claim 1,
The threshold value is set larger than the force feedback value at the time of non-contact in the vicinity of the force feedback value at the time of non-contact between the mechanism portion (24) and the workpiece (28). Processing machine. The processing machine according to claim 1, wherein
The processing machine characterized in that the force detection means (32, 56) detects a strain generated in the structure portion and detects the force from the detected strain. A power source (12), a mechanism portion (24) that receives power from the power source and moves to apply a machining force to the workpiece (28); and a structure portion (26) that supports the mechanism portion and the workpiece. In a method for controlling a processing machine (10) comprising:
Detecting the position of the mechanism part;
Generating a first control command based on the detected position;
Detecting the machining force output from the mechanism unit;
Generating a second control command based on the detected force;
Selecting one of the first control command and the second control command, and controlling the power source based on the selected control command;
In the selecting step, the second control command from the position control unit is selected while the mechanism unit is approaching the workpiece, and the detected processing force is compared with a predetermined threshold value. As a result of the comparison, if the detected machining force is smaller than the threshold value, the second control command is still selected, and if the detected machining force is equal to or greater than the threshold value as a result of the comparison, Selecting the first control command from the force control means;
A method for controlling a processing machine.

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