Power tool with automatic downshift feature

• US 5,637,968 A
• Filed: 10/25/1993
• Issued: 06/10/1997
• Est. Priority Date: 10/25/1993
• Status: Expired due to Term

• Current Assignee: Stanley Works Limited (Stanley Black & Decker, Inc.)
• Original Assignee: Stanley Works Limited (Stanley Black & Decker, Inc.)
• Inventors: Kainec, Stephen M., Naumann, William L.
• Primary Examiner(s): Sircus, Brian
• Application Number:
  US08/141,783
• Time in Patent Office: 1,324 Days
• Field of Search: 318/432, 318/433, 318/434, 388/937, 173/4-7, 173/217, 173/93.5, 81/467, 81/469, 73/862.23, 73/862.24, 29/407, 29/707
• US Class Current: 318/432
• CPC Class Codes: B23P 19/066 by electrical means
• CPC Class Codes: B25B 23/14 Arrangement of torque limiters or torque indicators in wrenches or screwdrivers couplings for transmitting rotation or clutches F16D; devices for measuring torque per se G01L
• CPC Class Codes: B25F 5/001 Gearings, speed selectors, clutches or the like specially adapted for rotary tools
• CPC Class Codes: G05D 17/02 characterised by the use of electric means
• CPC Class Codes: Y10T 29/49764 with testing or indicating
• CPC Class Codes: Y10T 29/5303 Responsive to condition of work or product

Abstract

A method and apparatus for correcting torque overshoot in power tools wherein torque per angle rate is sensed on each rundown and the speed of the tool is automatically adjusted to maintain torque accuracy on higher torque rate joints while maintaining speed on lower torque rate joints, automatically minimizing tool heating and maximizing job rate. In the setting of threaded fasteners, joint rates are defined as high (hard), medium or low (soft). Two torque points are defined, a first torque point and a second torque point, which are percentages of the target torque, for example 25% and 50% respectively. Two angle values are defined corresponding to the number of degrees of tool spindle rotation measured along the portion of the torque/angle curve between the first torque point and the second torque point on typical linear hard and medium joints. Two final tightening speeds are defined as percentages of full speed corresponding to the tool system requirements for accurate shutoff on the two types of joints, hard and medium. A controller counts the number of angle degrees between the first torque point and the second torque point. The angle counted is compared with the values of hard and medium angles to determine the joint rate. If the angle is less than or equal to the hard angle, the joint is considered hard and the controller immediately downshifts the tool to the hard speed. If the angle is greater than the hard angle but less than or equal to the medium angle, the joint is considered medium and the controller immediately downshifts the tool to the medium speed. If the angle is greater than the medium angle, the joint is considered soft and the speed is not changed.

Claims

1. A method for correcting for torque overshoot in an electric power tool to perform a fastening job wherein the tool is to be shut off at a target torque, said method comprising:

a) defining first and second torque points which are percentages of the target torque;

b) defining first and second angle values corresponding to tool spindle rotation to be measured between the first and second points for high torque rate and medium torque rate fastening jobs, respectively;

c) measuring the angle value between the first and second points during rundown of the tool while performing the fastening job;

d) comparing the measured angle value with pre-defined angle values for high torque rate and medium torque rate fastening jobs; and

e) utilizing the results of the comparison to perform the fastening job.

2. The method of claim 1, wherein said step of utilizing the results of the comparison comprises controlling the speed of the tool as the target torque is reached.

3. The method of claim 1, wherein said step of utilizing the results of the comparison comprises:

a) downshifting the tool to a speed providing accurate shutoff in high torque rate jobs if the measured angle value is less than or equal to the pre-defined angle value for high torque rate fastening jobs;

b) downshifting the tool to a speed providing accurate shutoff in medium torque rate jobs if the measured angle value is less than or equal to the pre-defined angle value for medium torque rate fastening jobs; and

c) maintaining the tool speed when the measured angle value is greater than the pre-defined angle value for medium torque rate fastening jobs.

4. The method of claim 1, wherein said first and second torque points are 25 percent and 50 percent, respectively, of the target torque.

5. A method for correcting for torque overshoot in an electric power tool to perform a fastening job wherein the tool is to be shut off at a target torque, said method comprising:

a) defining first and second torque points which are percentages of the target torque;

b) defining first and second angle values corresponding to the tool spindle rotation measured between the first and second points for high torque rate and medium torque rate fastening jobs, respectively;

c) defining first and second final tightening tool speeds as percentages of full speed corresponding to requirements for accurate tool shut off on high torque rate and medium torque rate fastening jobs, respectively;

d) measuring the angle value between the first and second torque points during rundown of the tool while performing the fastening job;

e) comparing the measured angle value with the first and second defined angle values;

f) downshifting the tool to the first defined final tightening speed if the measured angle value is less then or equal to the first defined angle value;

g) downshifting the tool to the second defined final tightening speed if the measured angle value is less than or equal to the second defined angle value; and

h) maintaining the tool speed when the measured angle value is greater than the second defined angle value.

6. The method of claim 5, wherein said first and second torque points are 25 percent and 50 percent, respectively, of the target torque.

7. A system for correcting for torque overshoot in an electric power tool driven by an electric motor wherein the tool is to be shut off at a target torque, said motor having speed control means operatively associated therewith, said system comprising:

a) resolver means for providing angle information relating to degrees of rotation of said tool;

b) torque transducer means for providing torque information relating to the job being performed by said tool; and

c) controller means connected to said resolver means and to said torque transducer means for utilizing said angle information and said torque information to control the speed of said tool, said controller means comprising means for measuring the angle value between first and second torque points along a torque/angle curve of the job being performed by said tool during rundown of said tool while the job is being performed, means for comparing the measured angle value with predefined angles for high torque rate and medium torque rate jobs and means for utilizing the results of the comparison in connection with controlling said tool during the job.

8. The system of claim 7 wherein said means for utilizing the results of the comparison comprises:

a) means for downshifting said tool to a speed providing accurate shutoff in high torque rate jobs if the measured angle value is less than or equal to a pre-defined angle value for high torque rate jobs;

b) means for changing said tool speed to a speed providing accurate shutoff in medium torque rate jobs if the measured angle value is less than or equal to a pre-defined angle value for medium torque rate jobs; and

c) means for maintaining the tool speed when the measured angle value is greater than the pre-defined angle value for medium torque rate jobs.

9. A system for correcting for torque overshoot in an electric power tool driven by an electric motor wherein the tool is to be shut off at a target torque, said system comprising:

a) means for providing angle information relating to degrees of rotation of said tool;

b) means for providing torque information relating to the job being performed by said tool; and

c) control means connected to said means for providing angle information and to said means for providing torque information for utilizing said angle information and said torque information to control the speed of said tool during fastener rundown and prior to tool shutoff;

said control means including automatic downshift means comprising;

1) means for obtaining the angle information between two predetermined torque points on the torque/angle curve for the job being performed by said tool;

2) means for comparing the obtained angle information to predetermined angle values for high torque rate and medium torque rate jobs; and

3) means for downshifting said tool to one of two final rundown speeds depending upon the results of the angle comparison.