Screw tightening system, controller, and non-transitory storage medium

Patent metadata

Field	Value
Publication number	US-12440933-B2
Application number	US-202318163395-A
Country	US
Kind code	B2
Filing date	Feb 2, 2023
Priority date	Feb 28, 2022
Publication date	Oct 14, 2025
Grant date	Oct 14, 2025

Abstract

A screw tightening system includes an actuator including a driver bit that rotationally drives a screw and a motor coupled with driver bit, and a controller that controls actuator. Controller includes an acquirer that acquires torque values of a torque generated in a motor, a calculator that calculates a standard deviation of the torque values in a temporary tightening period, and a determiner that determines that there is an abnormality when a ratio of the standard deviation to a reference standard deviation exceeds a first threshold value.

First claim

What is claimed is:

1. A screw tightening system comprising:
an actuator including a driver bit configured to rotationally drive a screw, a motor coupled with the driver bit, a driver configured to drive the motor, and a load sensor configured to detect an axial load on the driver bit; and a controller configured to control the actuator,
wherein:
the driver is configured to calculate a torque value of a torque generated in the motor,
the controller includes:
an acquirer configured to acquire torque values of the torque from the driver,
a calculator configured to calculate a standard deviation of the torque values acquired in a temporary tightening period from when the screw engages with a screw hole until when the screw is seated in the screw hole, and
a determiner configured to determine that there is an abnormality when a ratio of the standard deviation to a reference standard deviation exceeds a first threshold value, and

the determiner is configured to determine that there is an abnormality when the ratio does not exceed the first threshold value and the axial load detected by the load sensor exceeds a second threshold value.

2. The screw tightening system according to claim 1 , wherein the controller further includes a commander configured to command the motor to stop when is the determiner determines that there is an abnormality.

3. The screw tightening system according to claim 1 , wherein
the acquirer is configured to acquire the torque values at a predetermined cycle from the driver, and
the calculator is configured to start calculation of the standard deviation when the torque value is acquired a first predetermined number of times or more in the temporary tightening period.

4. The screw tightening system according to claim 3 , wherein the calculator is configured to calculate the standard deviation by using the torque values acquired for all number of times from a start of the temporary tightening period to a present time.

5. The screw tightening system according to claim 3 , wherein the calculator is configured to calculate the standard deviation by using the torque values for a latest second predetermined number of times.

6. The screw tightening system according to claim 1 , wherein the reference standard deviation is calculated based on the torque values acquired by the acquirer for all number of times in the temporary tightening period when the screw is considered to be normally tightened to the screw hole.

7. The screw tightening system according to claim 1 , wherein the reference standard deviation is an average value of standard deviations each of which is calculated based on the torque values acquired by the acquirer for a predetermined number of times in the temporary tightening period when the screw is considered to be normally tightened to the screw hole.

8. The screw tightening system according to claim 1 , wherein the determiner is configured to select one from a plurality of reference standard deviations depending on at least one of a size of the screw, a material of the screw, and a material of the screw hole.

9. The screw tightening system according to claim 1 , wherein the determiner is configured to select one from a plurality of first threshold values depending on at least one of the size of the screw, the material of the screw, and the material of the screw hole.

10. A controller configured to control an actuator including a driver bit configured to rotationally drive a screw, a motor coupled with the driver bit, and a driver configured to drive the motor and calculate a torque value of a torque generated in the motor, the controller comprising:
an acquirer configured to acquire torque values of the torque from the driver; a calculator configured to calculate a standard deviation of the torque values acquired in a temporary tightening period from when the screw engages with a screw hole until when the screw is seated in the screw hole; and a determiner configured to determine that there is an abnormality when a ratio of the standard deviation to a reference standard deviation exceeds a first threshold value,
wherein:
the actuator includes a load sensor configured to detect an axial load on the driver bit and
the determiner is configured to determine that there is an abnormality when the ratio does not exceed the first threshold value and the axial load detected by the load sensor exceeds a second threshold value.

11. A non-transitory storage medium configured to store a control program which when accessed and executed by one or more processors of a computer that is connected to an actuator including a driver bit configured to rotationally drive a screw, a motor coupled with the driver bit, a driver configured to drive the motor and calculate a torque value of a torque generated in the motor, and a load sensor configured to detect an axial load on the driver bit, is configured to cause the one or more processors to:
acquire torque values of the torque from the driver,
calculate a standard deviation of the torque values acquired in a temporary tightening period from when the screw engages with a screw hole until when the screw is seated in the screw hole,
determine that there is an abnormality when a ratio of the standard deviation to a reference standard deviation exceeds a first threshold value, and
determine that there is an abnormality when the ratio does not exceed the first threshold value and the axial load detected by the load sensor exceeds a second threshold value.

Assignees

• Omron Tateisi Electronics Co

Inventors

• Biwaki Shu
• Liu Zhiqiang
• Murai Masahiro
• Tsuchihashi Yuki

Classifications

• B25B23/147

  specially adapted for electrically operated wrenches or screwdrivers · CPC title

• B23P19/066 Primary

  by electrical means · CPC title

• G05B2219/45091

  Screwing robot, tighten or loose bolt · CPC title

• B25J9/1679

  characterised by the tasks executed · CPC title

• G05D17/02

  characterised by the use of electric means · CPC title