Controlling load ratio induced shut-down conditions in numerical control devices

• US 10,088,828 B2
• Filed: 10/21/2015
• Issued: 10/02/2018
• Est. Priority Date: 10/24/2014
• Status: Active Grant

• Current Assignee: Okuma Corporation
• Original Assignee: Okuma Corporation
• Inventors: Kawai, Yoichi
• Primary Examiner(s): Ali, Mohammad
• Assistant Examiner(s): Booker, Kelvin
• Application Number:
  US14/919,040
• Publication Number:
  US 20160116900A1
• Time in Patent Office: 1,077 Days
• CPC Class Codes: G05B 19/4062 Monitoring servoloop, e.g. overload of servomotor, loss of feedback or reference
• CPC Class Codes: G05B 2219/37429 Temperature of motor
• CPC Class Codes: G05B 2219/42281 If estimated temperature rise of motor is too high, inhibit motor

Abstract

A numerical control device with a function to prevent a problem caused by a rapid stop of a processing operation due to a motor overheating during processing. A temperature comparator obtains a load ratio T/Tmax or Tw/Tmax which is a ratio of the motor temperature T or predicted temperature Tw to a maximum allowable temperature Tmax stored in a storage device. When the load ratio T/Tmax or Tw/Tmax is over a threshold Tp stored in a storage, the device is placed in an alarm mode to shutdown the power supply to the motor after the processing program is executed to the end of a sequence block or the end of the processing program.

Claims

1. A numerical control device comprising:

an NC command generator that outputs a positional command by executing a processing program;

a position controller that receives inputs of the positional command and a positional feedback from an encoder sensing a position of a movable element of a motor, obtains a speed command based on the received inputs, and outputs the speed command;

a speed controller that receives inputs of the speed command and a speed feedback from the encoder, obtains a current command based on the received inputs, and outputs the current command;

a current controller that receives inputs of the current command and a current feedback, obtains an inverter drive command based on the received inputs, and outputs the inverter drive command;

an inverter circuit that controls the motor in accordance with the inverter drive command;

a motor temperature sensor that senses a temperature of the motor or calculates a temperature of the motor based on the current command or the current feedback; and

a power supply controller that

calculates a load ratio that is a ratio of the motor temperature sensed or calculated by the motor temperature sensor to a predetermined maximum motor allowable temperature, and

controls to shutdown a power supply to the motor after allowing the NC command generator to execute the processing program to an end of a sequence block or an end of the processing program when the calculated load ratio is over a predetermined threshold.

2. The numerical control device according to claim 1, wherein the threshold is set to a lower value when a time period required for one cycle of the processing program is longer.

3. The numerical control device according to claim 1, further comprising a display that displays the load ratio calculated by the power supply controller.

4. A method comprising:

outputting a positional command by executing a processing program by an NC command generator;

receiving inputs of the positional command and a positional feedback from an encoder sensing a position of a movable element of a motor, obtaining a speed command based on the received inputs, and outputting the speed command;

receiving inputs of the speed command and a speed feedback from the encoder, obtaining a current command based on the received inputs, and outputting the current command;

receiving inputs of the current command and a current feedback, obtaining an inverter drive command based on the received inputs, and outputting the inverter drive command;

controlling the motor in accordance with the inverter drive command;

sensing a temperature of the motor or calculating a temperature of the motor based on the current command or the current feedback; and

calculating a load ratio that is a ratio of the sensed or calculated motor temperature to a predetermined maximum motor allowable temperature, and shutting down a power supply to the motor after allowing the NC command generator to execute the processing program to an end of a sequence block or an end of the processing program when the calculated load ratio is over a predetermined threshold.

5. A numerical control device comprising:

an NC command generator that outputs a positional command by executing a processing program;

a position controller that receives inputs of the positional command and a positional feedback from an encoder sensing a position of a movable element of a motor, obtains a speed command based on the received inputs, and outputs the speed command;

a speed controller that receives inputs of the speed command and a speed feedback from the encoder, obtains a current command based on the received inputs, and outputs the current command;

a current controller that receives inputs of the current command and a current feedback, obtains an inverter drive command based on the received inputs, and outputs the inverter drive command;

an inverter circuit that controls the motor in accordance with the inverter drive command;

a motor temperature sensor that senses a temperature of the motor or calculates a temperature of the motor based on the current command or the current feedback; and

a cut depth controller that

calculates a load ratio that is a ratio of the motor temperature sensed or predicted by the motor temperature sensor to a predetermined maximum motor allowable temperature, and

controls to reduce a cut depth commanded by the processing program when the calculated load ratio is over a predetermined threshold.

6. The numerical control device according to claim 5, wherein the threshold is set to a lower value when a time period required for one cycle of the processing program is longer.

7. The numerical control device according to claim 5, further comprising a display that displays the load ratio calculated by the cut depth controller.

8. A method comprising:

outputting a positional command by executing a processing program by an NC command generator;

receiving inputs of the positional command and a positional feedback from an encoder sensing a position of a movable element of a motor, obtaining a speed command based on the received inputs, and outputting the speed command;

receiving inputs of the speed command and a speed feedback from the encoder, obtaining a current command based on the received inputs, and outputting the current command;

receiving inputs of the current command and a current feedback, obtaining an inverter drive command based on the received inputs, and outputting the inverter drive command;

controlling the motor in accordance with the inverter drive command;

sensing a temperature of the motor or calculating a temperature of the motor based on the current command or the current feedback; and

calculating a load ratio that is a ratio of the sensed or calculated motor temperature to a predetermined maximum motor allowable temperature, and controlling to reduce a cut depth commanded by the processing program when the calculated load ratio is over a predetermined threshold.