Servo motor control unit for press-forming machine

• US 20060012326A1
• Filed: 06/28/2005
• Published: 01/19/2006
• Est. Priority Date: 06/28/2004
• Status: Active Grant

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Okita, Tadashi, Iwashita, Yasusuke, Kawamura, Hiroyuki
• Granted Patent: US 7,049,775 B2
• Time in Patent Office: Days
• US Class Current: 318/645
• CPC Class Codes: B30B 15/0094 Press load monitoring means B30B15/281 takes precedence
• CPC Class Codes: B30B 15/148 Electrical control arrangements
• CPC Class Codes: G05B 19/416 characterised by control of velocity, acceleration or deceleration G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/41202 Structure, compensation circuit after comparator in loop
• CPC Class Codes: G05B 2219/42087 Speed and force loop
• CPC Class Codes: G05B 2219/42092 Position and force control loop together

Abstract

A servo motor for driving a die is provided with position and speed detectors. Further, a pressure sensor for detecting the pressure applied to a workpiece is provided. In the servo motor control unit, the smaller one of the speed command obtained by feedback control of the position and the speed command obtained by the pressure feedback control is selected as an output of a comparator. Based on the speed command output from the comparator, feedback control of the speed is performed and the servo motor is driven. In the state where the die does not press against the workpiece, a pressure error is large, the speed command by pressure control becomes large, and the speed command by position control becomes small. Therefore, position control is performed. When the workpiece is pressed, the position error increases, and the pressure error decreases, a speed command by pressure control is employed and pressure control is performed.

Claims

1. A servo motor control unit for a press-forming machine comprising a position detector for detecting a position of a die fastening member of said press-forming machine or a servo motor for driving said die fastening member, a speed detector for detecting a speed of said servo motor, a position control processing part for preparing a speed command from a position error comprised of a difference between a position command and a position feedback, and a speed control processing part for preparing a torque command from a speed error comprised of a difference between the speed command and a speed feedback, said servo motor control unit adapted to drive said servo motor based on the prepared torque command to machine a workpiece,

wherein said servo motor control unit further comprises:

a pressure detector for detecting an actual pressure applied to said workpiece;

a pressure control processing part for preparing a speed command from a pressure error comprised of a difference between a pressure command and the actual pressure;

a comparing means for comparing the speed command output from said position control processing part with the speed command output from said pressure control processing part; and

a switching means for selecting, based on the results of comparison at said comparing means, one of the speed command output from said position control processing part and the speed command output from said pressure control processing part and transferring the selected speed command to said speed control processing part.

2. The servo motor control unit according to claim 1, wherein said switching means designates a direction of pressing against said workpiece as positive, selects the smaller speed command between the speed command output from said position control processing part and the speed command output from said pressure control processing part as an actual speed command, and transfers the selected speed command to said speed control processing part.

3. The servo motor control unit according to claim 1, wherein said comparing means compares an absolute value of the speed command output from said position control processing part with an absolute value of the speed command output from said pressure control processing part, and said switching means selects the speed command with the smaller absolute value between the speed command output from said position control processing part and the speed command output from said pressure control processing part as an actual speed command and transfers the selected speed command to said speed control processing part.

4. The servo motor control unit according to claim 1, wherein said comparing means compares an absolute value of the speed command output from said position control processing part with an absolute value of the speed command output from said pressure control processing part, and said switching means selects the speed command output from said position control processing part when the absolute value of the speed command output from said position control processing part is smaller than the absolute value of the speed command output from said pressure control processing part, selects the speed command output from said pressure control processing part after it is detected that the absolute value of the speed command output from said pressure control processing part becomes smaller than the absolute value of the speed command output from said position control processing part, and transfers the selected speed command to said speed control processing part.

5. The servo motor control unit according to claim 1, further comprising a means for detecting an actual acceleration of said servo motor and correcting the torque command by a torque corresponding to the detected acceleration.

6. The servo motor control unit according to claim 1, wherein the position command and pressure command are simultaneously given from a host control unit.

7. The servo motor control unit according to claim 1, wherein said press-forming machine is adapted so that one die fastening member reciprocates by a predetermined stroke and that the other die fastening member operates as a die cushion, said servo motor is a servo motor for driving said die fastening member operating as the die cushion, and said switching means has a feed forward means for adding a feed forward control amount obtained based on the differentiated value of said position command to an actual speed command when selecting the speed command output from said pressure control processing part as the actual speed command.

8. A servo motor control unit for a press-forming machine comprising a position detector for detecting a position of a die fastening member of said press-forming machine or a servo motor for driving said die fastening member, a speed detector for detecting a speed of said servo motor, a position control processing part for preparing a speed command from a position error comprised of a difference between a position command and a position feedback, and a speed control processing part for preparing a torque command from a speed error comprised of a difference between the speed command and a speed feedback, said servo motor control unit adapted to drive said servo motor based on the prepared torque command to machine a workpiece,

wherein said servo motor control unit further comprises:

a pressure detector for detecting an actual pressure applied to said workpiece;

a pressure control processing part for preparing a torque command from a pressure error comprised of a difference between a pressure command and the actual pressure;

a comparing means for comparing the torque command output from said speed control processing part with the torque command output from said pressure control processing part; and

a switching means for selecting and outputting, based on the results of comparison at said comparing means, one of the torque command output from said speed control processing part and the torque command output from said pressure control processing part.

9. The servo motor control unit according to claim 8, wherein said switching means selects and outputs, from between the torque command output from said speed control processing part and the torque command output from said pressure control processing part, the torque command giving the smaller pressure applied to the workpiece as an actual torque command.

10. The servo motor control unit according to claim 8, wherein said comparing means compares an absolute value of the torque command output from said speed control processing part with an absolute value of the torque command output from said pressure control processing part, and said switching means selects and outputs, from between the torque command output from said speed control processing part and the torque command output from said pressure control processing part, the torque command with the smaller absolute value as an actual torque command.

11. The servo motor control unit according to claim 8, wherein said comparing means compares an absolute value of the torque command output from said speed control processing part with an absolute value of the torque command output from said pressure control processing part, and said switching means selects the torque command output from said speed control processing part when the absolute value of the torque command output from said speed control processing part is smaller than the absolute value of the torque command output from said pressure control processing part, selects the torque command output from said pressure control processing part after it is detected that the absolute value of the torque command output from said pressure control processing part becomes smaller than the absolute value of the torque command output from said speed control processing part, and outputs the selected torque command as an actual torque command.

12. The servo motor control unit according to claim 8, further comprising a means for detecting the actual acceleration of the servo motor and correcting the torque command by a torque corresponding to the detected acceleration.

13. The servo motor control unit according to claim 8, wherein the position command and pressure command are simultaneously given from a host control unit.

14. The servo motor control unit according to claim 8, wherein said die fastening member driven by said servo motor moves in the vertical direction, and said comparing means corrects the torque command output from said speed control processing part by a gravity offset value corresponding to the gravity load applied to said servo motor and compares the corrected torque command and the torque command output from said pressure control processing part.