Position control apparatus

• US 6,457,964 B1
• Filed: 08/18/2000
• Issued: 10/01/2002
• Est. Priority Date: 08/19/1999
• Status: Expired due to Term

• Current Assignee: Toshiba Machine Company Limited
• Original Assignee: Toshiba Machine Company Limited
• Inventors: Yamaguchi, Yutaka, Nishizawa, Makoto, Yamazaki, Takashi, Suzuki, Masamitsu, Furuno, Takahiro
• Primary Examiner(s): HEITBRINK, TIMOTHY W
• Application Number:
  US09/640,909
• Time in Patent Office: 774 Days
• Field of Search: 425/150, 425/542, 264/40.5
• US Class Current: 425/150
• CPC Class Codes: B29C 2945/7602 Torque
• CPC Class Codes: B29C 2945/76033 Electric current or voltage
• CPC Class Codes: B29C 2945/7612 rotational movement
• CPC Class Codes: B29C 2945/7623 clamping or closing drive means
• CPC Class Codes: B29C 2945/76525 Electric current or voltage
• CPC Class Codes: B29C 2945/76568 Position
• CPC Class Codes: B29C 2945/76742 movable
• CPC Class Codes: B29C 2945/76943 compare with thresholds
• CPC Class Codes: B29C 45/80 of relative position of mould parts
• CPC Class Codes: B29C 45/84 Safety devices B29C45/7626 takes precedence

Abstract

In a position control apparatus, the rate and the torque of the servomotor are monitored, wherein when it is detected that the servomotor is locked, the torque is limited, so that renewal of a command position to be supplied to the servomotor driving unit is stopped.

Claims

1. A position control apparatus comprising:

a servomotor for driving a movable part of a motor-driven injection molding machine;

position command means for renewing a position command value of the movable part, the position command value being output in a predetermined cycle in accordance with a positional error between a present position of the movable part and a target position of the movable part;

limiting means for limiting a current value supplied to the servomotor, when the positional error between the present position of the movable part and the target position of the movable part is equal to or greater than a predetermined value or a rotation rate of the servomotor is equal to or smaller than a predetermined value; and

means for stopping a renewal of the position command value or extending a renewal cycle thereof, when the current value is limited.

2. A position control apparatus comprising:

a servomotor for moving a movable mold of a motor-driven injection molding machine to a fixed mold thereof;

a servomotor driving unit;

a command position setting unit for setting a command on a command position of the movable mold, a command rotation rate of the servomotor and a command current value of a current supplied to the servomotor; and

a command position control unit for controlling the servomotor driving unit in accordance with the command set by the command position setting unit, said servomotor driving unit comprising;

means for detecting a positional error between a present position of the movable mold and the positional command;

means for detecting a rate error between a present rotation rate and the command rotation rate of the servomotor;

a rate feedback control portion for outputting a limit torque command, when the positional error is equal to or greater than a predetermined value and the rate error is equal to or smaller than a predetermined value; and

a current control portion for supplying a torque limit current to the servomotor, when a current, flowing through the servomotor while the limit torque command is output, exceeds a predetermined value,

wherein when the torque limit current is supplied to the servomotor, renewal of the command position supplied from the command position setting unit to the servomotor driving unit is stopped.

3. A position control apparatus comprising:

a servomotor for moving a movable mold of an injection molding machine to a fixed mold thereof;

a servomotor driving unit;

a command position control unit for renewing in every unit time a target position of the movable mold based on a moving rate and a present position of the movable mold and supplying a command position to the servomotor driving unit;

a command position setting unit for supplying a moving position, the moving rate and a limit torque value of the movable mold to the command position control unit,

said servomotor driving unit including a current output portion, an output current value detecting sensor, a current feedback control portion for controlling the current output portion so that an output current value coincides with a current command value, a rate detecting sensor for detecting a servomotor rotation rate, a rate feedback control portion for controlling the current feedback control portion so that the servomotor rotation rate coincides with a rotation rate command value, a movable mold position sensor, and a position control portion for controlling the rate feedback control portion so that the present position of the movable mold coincides with a position command value thereof,

wherein when a torque limit current is supplied to the servomotor, renewal of the command position supplied from the command position control unit to the servomotor driving unit is stopped.

4. A position control apparatus according to claim 3, wherein:

the command position control unit includes means for stopping renewal of the positional command in every time unit by a limit torque output signal output from the servomotor driving unit; and

the servomotor driving unit includes means for limiting the output current value by the limit torque value and means for outputting the limit torque output signal in a case where the output current is limited by the limit torque value, and for stopping renewal of the command position supplied to the servomotor driving unit, when an output torque of the servomotor reaches the limit torque value while the movable mold is moving.

5. A position control apparatus according to claim 3, wherein the rate feedback control portion has means for outputting a limit torque output signal for supplying to the current feedback control portion a command for limiting a current command to a limit torque.

6. A position control apparatus according to claim 3, wherein the rate feedback control portion has means for outputting a limit torque output signal to the command position control unit in order to supply a limit current command value calculated from a limit torque command value to the current feedback control portion.

7. A position control apparatus according to claim 3, wherein the command position control unit has means for stopping renewal of the command position in every time unit, in a case where torque commands transmitted from the servomotor driving unit coincide, and the servomotor driving unit has means for converting an output current to torque and transmitting the torque to the command position control unit.