In the art of testing torque wrenches, it is common practice to provide special machines in and with which torque wrenches to be tested and/or calibrated (adjusted) can be easily and conveniently engaged and that operate to direct operating forces onto and through the wrenches in an accurate and prescribed manner and that enable the operators of the machines to determine the accuracy of and to adjust or calibrate the wrenches.
Torque wrenches that can be tested and calibrated in such machines vary widely in details of construction. Such wrenches characteristically include elongate lever arms with front and rear ends; hand grips at the rear ends of the lever arms; work-engaging heads projecting radially from the other or front ends of the lever arms; and, force-indicating means that serve to advise the operator of the wrenches of the torsional forces conducted by the heads onto related work. The work-engaging heads for such wrenches are, most often, polygnal members that are engageable in polygonal openings in work parts or related tools, such as drive sockets.
At the time of manufacturing torque wrenches, their forceindicating means are calibrated, adjusted and set so that the wrenches are accurate when first put to use. During normal use of such wrenches, they tend to become maladjusted and must be periodically tested for accuracy and recalibrated when that is required.
To effectively test and calibrate torque wrenches, the prior art has provided several different kinds of torque wrench calibrating machines in and with which torque wrenches can be easily and conveniently engaged and that function to operate the wrenches in a prescribed manner and to accurately indicate those forces that are directed onto and through the wrenches. Those forces that are indicated by the calibrating machines (called calibrating forces) are compared with those forces that are indicated by the force-indicating means of the wrenches (called calibrated forces). If the calibrating and calibrated forces are not the same, the force-indicating means of the wrenches are suitably adjusted and set so that they are the same.
In the past, torque calibrating machines of the character referred to above were rather simple mechanical devices with input shafts with which the tool-engaging heads of wrenches to be tested were engaged and that included force-indicating means that operated to indicate the torsional forces directed by the wrenches onto the shafts. The wrenches were manually turned to effect testing thereof. Due to the inability of skilled operators of those old machines to accurately apply forces onto and through the wrenches, the dependability and accuracy of those old machines was determined to be wanting. That is, the forces manually applied to the wrenches were often misdirected and shakely, wobbly or otherwise unsteady.
As a result of the above, new, more accurate and dependable torque calibrating machines have been developed and are now in use. These new machines include electromechanical load cell transducers with which the work-engaging heads of wrenches to be tested are drivingly coupled; stop means that engage the handles of the wrenches in a prescribed manner; and, drive means to deliver work forces onto and through the wrenches in a steady and prescribed manner. In some instances, the drive means operate to pivot the arms of the wrenches about the pivotal axes of their work-engaging heads to torque the transducers and in which case the transducers are reaction parts for the wrenches. In other instances, the stop means engaging the handles of the wrenches and the drive means operate to rotate the tranducers, in which case the wrenches are reaction parts for the transducers. For practical reasons, it is preferred that the wrench lever arms be held stationary and that the transducers be rotated. In either case, when testing wrenches with such calibrating machines, parts of both the wrenches and the machines are yieldingly biased and are, in effect, spring-loaded. As a result of the spring loading of parts, the assemblies of parts tend to vibrate, reciprocate, recoil or otherwise work in an adverse fashion if steps are not taken to prevent such working of parts. To this end, the prior art has resorted to the use of manually driven gear transmissions characterized by manually-engageable hand wheels or cranks at their work-input ends and the output ends of which are suitably mechanically coupled with those parts of the machines that direct forces onto and through the wrenches. The transmissions afford great mechanical advantage to the operator of the machines and enables the operators to apply great forces into and through the machines and the wrenches related thereto in a slow, positive and steady fashion.
In addition to the foregoing, the transmissions include screw gears with follower nuts at their power output ends and that serve to lock the transmissions when the screw gears are not turned and to thereby prevent those parts worked upon and biased by the transmission from reciprocating and/or recoiling in a manner that is likely to adversely effect operation of the machines.
While those calibrating machines of the prior art that include transducers and transmissions of the general character referred to above are highly effective and dependable when put to careful and proper use, there is no sense of feel between the input and output ends of the transmissions and no sense of the forces directed onto and through the transducers. As a result, the forces directed onto and through the transducers can easily and quickly exceed the structural and functional limits of the transducers, causing irreparable damage thereto. Such damage to the transducers, however slight, renders the machines defective and/or undependable and is seldom noticed until such time as the transducers are themselves tested by other, separate and independent testing equipment.
As a result of the susceptibility of the above-noted kinds of calibrating machines to be damaged by over-stressing the transducers thereof, those who own and maintain such calibrating machines have found it to be necessary that access to and use of those machines be restricted and carefully monitored in order to avoid the likelihood that unskilled and careless hands will cause irreparable and costly damage to the machines.
As a result of the foregoing, the testing and calibrating of torque wrenches is, most often, a specialized activity that is slow and inconvenient to perform and that often fails to attain full potential use of the calibrating machines.