US3825912A

US3825912A - Torque wrench monitor

Info

Publication number: US3825912A
Application number: US00378664A
Authority: US
Inventors: D Wiese; R Sawicki
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1973-07-12
Filing date: 1973-07-12
Publication date: 1974-07-23
Anticipated expiration: 1991-07-23

Abstract

A circuit for providing an indication each time a threaded element has been properly tightened by a power torque wrench. A first switch is actuated upon the initiation of operation of the torque wrench to enable a capacitor to be charged at a predetermined rate. A second switch is responsive to the achievement of a predetermined torque output by the torque wrench to couple the charge across the first capacitor to the base of a transistor through a second capacitor. If the elapsed time between the actuation of the first switch and the actuation of the second switch is greater than a predetermined minimum, the signal coupled to the base electrode of the transistor is sufficient to bias the transistor into conduction to energize a lamp for providing an indication that the bolt has been properly tightened.

Description

United States Patent 1 Wiese et .al.

[ July 23, 1974 TORQUE WRENCH MONITOR [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: July 12, 1973 [21] Appl. No.: 378,664

[52] US. Cl 340/213 R, 340/220, 340/219, 340/267 R, 81/525, 307/272, 328/1 [51] Int. Cl. G081! 23/00 [58] Field ofSearchm; 340/213 R, 220, 419, 267 R, 340/421; 307/254, 27 2, 278, 308; 328/1,

Primary ExaminerJohn W. Caldwell Assistant Examiner-Richard P. Lange Attorney, Agent, or Firm-Howard N. Conkey 57 ABSTRACT- A circuit for providing an indication each time a threaded element has been properly tightened by a power torque wrench. A first switch is actuated upon the initiation of operation of the torque wrench to enable a capacitor to be charged at a predetermined rate. A second switch is responsive to the achievement of a predetermined torque output by the torque wrench to couple the charge across the first capacitor to the base of a transistor through a second capacitor. If the elapsedtime between the actuation of the first switch and the actuation of the second switch is greater than a predetermined minimum, the signal coupled to the base electrode of the transistor is sufficient to bias the transistor into conduction to energize a lamp for providing an indication that the bolt has been properly tightened.

2 Claims, 1 Drawing Figure [56] References Cited UNITED STATES PATENTS 2,512,032 6/1950 Mellert 8l/52.5 3,613,017 10/1971 Howells 328/206 3,664,186 I 5/1972 Kraus 81/525 representing that the threaded element being tightened has been properly tightened thereby.

' In the operation of a power torque wrench with the objective of turning down and tightening a threaded element to a specified torque, one of three possible events will occur: the specified torque will never be obtained, the specified torque will be arrived at too soon indicating that the threaded element has-not been properly turned down by reason, for example, of crossthreading or the cycling of the power torque wrench on a previously tightened element, and the specified torque will-be reached after a predetermined minimum period of time. In the last instance only, the threaded element has been properly tightened. It is the general object of this invention to provide an indication when a threaded element has been properly turned down and tightened by a power torque wrench.

It is another object of this invention to provide for a circuit which generates a signal indicating that a specified torque has been achieved by a power torque wrench after a predetermined minimum period of time following the initiation of the operation-of the power torque wrench;

These and other objects of this invention are accomplished by a timing circuit which is energized upon the initiation of the operation of the power torque wrench, the timing circuit generating a voltage having a magnitude increasing proportional to time. Upon the achievement of a specified torque by the power torque wrench, this voltage is coupled through a capacitor to the base electrode of a transistor. if the elapsed time between the initiation of operation of the power torque wrench and the achievement of the specified torque exceeds a minimum time required for the proper tightening of a threaded element, the magnitude of the pulse coupled to the base electrode of the transistor through the capacitor is of such a magnitude as to bias the transistor into conduction. Conduction of the transistor effects the energization of a lamp to provide an indication that the threaded element has been properly tightened.

The objects of this invention may be best understood by the following description of a preferred embodiment and the single figured drawing which is an electrical I schematic of the circuit of the preferred embodiment for providing an indication when a threaded element has been properly tightened by a power torque wrench.

Referring to the drawing, the circuit for providing an indication when a power torque wrench has properly 'turned down and tightened a threaded element includesa DC power supply comprised of a DC bat- "regulated'voltage is supplied from across the Zener diode 16. Although the DC power source 10 is shown to include a DC battery 12, it is understood that a rectified alternating voltage supply could be substituted therefor.

A normally open switch 18 is series coupled with a relay coil 20 across a Zener diode 16. The normally open switch 18 is mechanically associated with the power torque wrench so as to be closed upon the initiation of operation thereof. A normally open switch 22 is series coupled with a relay coil 24 across the Zener diode 16. The normally open switch 22 is mechanically associated with the power torque wrench and is responsive to the torque output thereof so as to be closed when a specified torque has been reached. A timing circuit includes-a capacitor 26 series coupled with a resistor 28 across the Zener diode 16. A set of normally closed relay contacts 30 are coupled in parallel with the capacitor 26 and are operated by the relay coil 20. A resistor 32 and a set of normally closed relay contacts 34 are series coupled across the capacitor 26. The set of normally closed relay contacts 34 are operated by the relay coil 24.

When both of the

relay coils

20 and 24 are deenergized, the capacitor 26 is short circuited by theset of normally closed relay contacts 30 and, consequently, is

- maintained discharged. When the relay coil 20 is energized, the timing circuit is enabled by the opening of the set of normally closed contacts 30 and the capacitor 26 is charged through the resistor 28 at a predeter mined rate to generate an output voltage proportional to the elapsedtime from the energization of the relay coil 20. Upon a subsequent energization of the relay coil 24, the set of normally closed relay contacts 34 are opened to couple the voltage across the capacitor 26 to an input circuit 36 of a PNP transistor 38 through a capacitor 40.

The input circuit 36 is comprised of a resistor 42 coupled between the capacitor and ground and a diode 44 having its anode coupled to the capacitor and its cathode coupled to the base electrode of the transistor 38. The emitter electrode of the transistor 38 is grounded and the collector electrode thereof is coupled to the cathode of the Zener diode 16 through a relay coil 46.

An indicating lamp 48 and a set of normally open relay contacts ,50 are series coupled across the series circuit comprised of the DC'battery l2 and the on-off .switch 13. The .set of normally open relay contacts 50 are operated by the relay coil 46. I

In operation, the regulated power supply 10 is energized upon the closure of the on-off switch 13. Thereafter, when operation of the power torque wrench is initiated to turn down a threaded element, the switch 18 is closed to energize the relay coil 20. Energization of the relay coil 20 opens the set of normally closed relay contacts 30 and the capacitor 26 begins to charge through the resistor 28. The voltage across the capacitor increases as a function of the elapsed time from the closure of the switch 18. Upon the achievement of a predetermined torque output of the power torque wrench, the switch 22 is closed to energize the relay coil 24. Energization of the relay coil 24 opens the set of normally closed relay contacts 34 to couple the voltage across the capacitor 26 to the series combination of the resistor 32, the capacitor 40, and the resistor 42.

, The resulting pulse coupled to the transistor 38 through the input circuit 36 has a magnitude related to the instantaneous magnitude of the charge on'the capacitor 26 when the set of normally closed relay contacts 34 are opened. The values of the resistor 32 and the capacitor 40 are such that if the elapsed time from the closure of the switch 18 to the closure of the switch 22 is equal to or greater than a predetermined minimum time required for the power torque wrench to properly turn down and tighten the threaded element to the predetermined torque, the magnitude of the charge on the capacitor 26 issuch that the magnitude of the pulse coupled 'to the base electrode of the transistor 38 through the'input circuit 36 biases the transistor 38 into conduction to energize the "relay coil 46. For elapsed times less than the predetermined minimum, the magnitude of the pulse coupled to the base electrode of the transistor is insufficient to bias the transistor 38 into conduction. Capacitor 26 does continue to charge while switch remains open. However, capacitor 40 is of such a value that it charges much faster than capacitor 26. The voltage drop'across capacitor 40 results in a continuously decreasing voltage on the base of transistor 38. Thus if relay coil 46 is not energized immediately after switch 34 opens, it will not be falsely energized later by the charging of capacitor 26. Energization of the relay coil 46 affects the closing of the normally open relay contacts 50 to energize the indicator lamp 48 to provide an indication that thethreaded element has been properly, turned down and. tightened.

If, after the initiation of the operation of the power torque wrench and the resultant closure of the switch 18, the predetermined torque is never achieved, the contact 22 remains in the open position. Consequently, the normally closed relay contacts 34 remain closed and no pulse is coupled to the transistor 38 which remains biased into nonconduction to maintain the indicator lamp 48 deenergized. If, after the initiation of the operation of the power torque wrench and the resultant closure of-theswitch 18, the predetermined torque is achieved before the minimum required elapsed time,

the resultant-pulse coupled to the-base electrode of the transistor 38 when the set of normally closed relay gize the

relay coils

20 and 24, respectively. The resultant closure of the sets of normally closed relay contacts 30 and 34 result in the discharge of the capacitors 26 and 40. The cycle is then repeated upon a subsequent operation of the power torque wrench.

To maintain the indicating lamp 48 energized fora set time period following the energization thereof, a time delay circuit 51 is provided. The time delay circuit 51 is comprised of a resistor 52, a capacitor 54 and a set of normally open relay contacts 56 series coupled between the base'electrode of the transistor 38 and the cathodeof the Zener diode 16. A discharge circuit for the capacitor 54 is comprised of a resistor 58 series coupled with a set of normally closed relay contacts 60 across the capacitor 54. The set of nonnally open relay contacts 56 and the set of normally closed relay contacts 60 are operated by the relay coil 46. When the transistor 38 is biased into conduction by the pulse supplied thereto through the capacitor 40, the resultant energization of the relay coil 46 closes the set of normally open relay contacts 56 and opens the set of nornally closed contacts 60. The capacitor 54 is charged through the resistor 52 at a predetermined rate. The current input to the base electrode of the transistor 38 while the capacitor 54 is charging is sufficient to maintain the transistor 38 in conduction to maintain the lamp 48 energized. After the capacitor 54 is charged,

the transistor 38 is again biased into nonconduction to deenergize the lamp 48. When the transistor 38 is biased into nonconduction, the relay coil 46 is deenergized to open the set of normally open relay contacts 56 and to close the set of normally closed relay contacts 60. Closure of the set of normally closed relay contacts 60 operates to discharge the capacitor 54 through the resistor 58. i

As can be seen-from the foregoing description, a circuit is provided, which gives an indication when a threaded element has been properly turned down and tightened by a power torque wrench as determined by the elapsedtime between the initiation of the operation of the power torque wrench and the achievement of predetermined torque.

The specific details of the power torque wrench and the various switches are not set forth in the foregoing description as those details are well known to one skilled in theart and can take any one of various forms. For example, the power torque wrench may be driven by any of various means such as by an electrical or pneumatic power. The detailed description of a preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art without departing from the scope of the invention.

We claim:

1. A circuit for providing an indication when a threaded element has been properly tightened by a power torque wrench comprising: first and second bistable switch means, each of said switch meanslbeing shiftable between respective first and second states; means responsive to the'initiation of operation of the power torque wrench for shifting the first bistable switch means to itssecond state; a timing'circuit coupled to the first switch means for generating an output voltage having a magnitude related to the elapsed time from the shifting of the firstbistable switch means to its second state, the magnitude of, the voltage being a set value after an elapsed time equal to a minimum time required for the power torque wrench to properly tighten the threaded element; means responsive to the achievement of a predetennined torque by the power torque wrench for shifting the second bistable switch means to its second state; indicating means; and means coupled to the timing circuit and the second bistable switch means for energizing the indicating means when the instantaneous magnitude of the output voltage when the second bistable switch means is shifted to its second state is equal to or greater than the set value, whereby the energization of the indicating means is an indication of the proper tightening of the threaded element by the power torque wrench;

2. A circuit for providing an indication when ,a threaded element has been properly tightened by a power torque wrench comprising: a DC power source; a timing circuit coupled in parallel with the DC power source, the timing circuit including a resistor and a first capacitor coupled in series; a first normally closed switch means coupled in parallel with the first capacitor; means responsive to the initiation of operation of the power torque wrench for opening the first normally closed switch means to enable the first capacitor to be charged by the DC power source to a voltage having a magnitude related to the elapsed time from the opening of the first normally closed switch means, the magni tude of the voltage being a set value after an elapsed time equal to a minimum time required for the power torque wrench to properly tighten a threaded element; a second normally nonconducting switch means, the second normally nonconducting switch means being responsive to a voltage signal supplied thereto having a magnitude equal to or greater than a predetermined bias level for shifting to a conducting state; a second capacitor having one side coupled to the second normally nonconducting switch means; means responsive to the achievement of a predetermined torque by the power to or greater than the set value; indicating means; andmeans responsive to the conduction of the second normally nonconducting switch means for coupling the indicating means in parallel with the DC power source to provide an indication of the proper tightening of the threaded element by the power torque wrench.

Claims

1. A circuit for providing an indication when a threaded element has been properly tightened by a power torque wrench comprising: first and second bistable switch means, each of said switch means being shiftable between respective first and second states; means responsive to the initiation of operation of the power torque wrench for shifting the first bistable switch means to its second state; a timing circuit coupled to the first switch means for generating an output voltage having a magnitude related to the elapsed time from the shifting of the first bistable switch means to its second state, the magnitude of the voltage being a set value after an elapsed time equal to a minimum time required for the power torque wrench to properly tighten the threaded element; means responsive to the achievement of a predetermined torque by the power torque wrench for shifting the second bistable switch means to its second state; indicating means; and means coupled to the timing circuit and the second bistable switch means for energizing the indicating means when the instantaneous magnitude of the output voltage when the second bistable switch means is shifted to its second state is equal to or greater than the set value, whereby the energization of the indicating means is an indication of the proper tightening of the threaded element by the power torque wrench.

2. A circuit for providing an indication when a threaded element has been properly tightened by a power torque wrench comprising: a DC power source; a timing circuit coupled in parallel with the DC power source, the timing circuit including a resistor and a first capacitor coupled in series; a first normally closed switch means coupled in parallel with the first capacitor; means responsive to the initiation of operation of the power torque wrench for opening the first normally closed switch means to enable the first capacitor to be charged by the DC power source to a voltage having a magnitude related to the elapsed time from the opening of the first normally closed switch means, the magnitude of the voltage being a set value after an elapsed time equal to a minimum time required for the power torque wrench to properly tighten a threaded element; a second normally nonconducting switch means, the second normally nonconducting switch means being responsive to a voltage signal supplied thereto having a magnitude equal to or greater than a predetermined bias level for shifting to a conducting state; a second capacitor having one side coupled to the second normally nonconducting switch means; means responsive to the achievement of a predetermIned torque by the power torque wrench for applying the voltage charge on the first capacitor to the second side of the second capacitor to charge the second capacitor and supply a voltage pulse to the second normally nonconducting switch means, the voltage pulse having a magnitude equal to or greater than the predetermined bias level when the magnitude of the voltage on the first capacitor is equal to or greater than the set value; indicating means; and means responsive to the conduction of the second normally nonconducting switch means for coupling the indicating means in parallel with the DC power source to provide an indication of the proper tightening of the threaded element by the power torque wrench.