Putting a new spin on measurement.
From the Latin word "torquere" meaning to twist, torque is a force to be reckoned with - and not just for tightening fasteners in automobile engines. Torque invades our everyday life, and without even thinking about it, we rotate or use products that rotate hundreds of times a day. The challenge in the past has been to monitor and measure torque accurately and economically in the manufacturing environment. Many attempts to control torque have been tried, including nondirect systems which monitor the levels of electric power drawn by a motor.
Now, a torque-sensing technology that is low in cost, accurate, reliable with low maintainability, and with a simplistic design can be integrated into existing equipment or compatible with new. The compact TorqStar series of noncontact torque sensors from Lebow Products, Troy, MI, a Siebe Group Co, includes both inline rotary and reaction-type sensors. TorqStar technology is said to provide an all-encompassing solution to the many torque monitoring and measuring challenges that have faced manufacturers and industrial users in the past. Its accuracy is reported to be within [+ or -] 0.5% of the full sensing scale.
In application, torque generated by the initial rotation of the sensor and tool, motor or other device, is measured and compensation offsets can be set prior to any work load being applied. Then, depending on the type of man/machine interface used, tolerance limits may be programmed into controllers, or display units set to provide readout to the operator. As torque encountered approaches and reaches these preset limits, the appropriate action can be taken. For example, the controller of an automated nut runner will shut down rotation and retract the spindle when the correct tightening has been achieved, a visual or audible alarm may be activated if proper torque, either under or over is not reached. The TorqStar can also be adapted to fit within the holder of a rotating cutting tool, or as part of an electric motor output shaft, as a component of a nut runner, or hand-held screw driver.
The potential applications for TorqStar sensors is enhanced when the torque measuring units are coupled with position or speed encoders, or rotation counters. In thread assembly operations such as bolted joints or bottle capping, these combined technologies deliver not only accurate and consistent tightening torque, but can also be used to detect cross threading or oversize male or undersize female threads where the preset force may be reached too early in the process as compared to the angle, and the torque signature does not correspond to its programmed setting.
Operationally, TorqStar does not use fancy formulas or intricate calculations. The two mechanical components of the TorqStar are a stainless steel shaft, diametrically sized for the appropriate torque range and a metal ring which fits tightly on the shaft. One journal on the shaft is machined with a precise taper on which the ring is assembled. The ring is made from a magnetoelastic titanium nickel material, producing no magnetic force when at rest. As soon as any rotational force is placed on the shaft, the slightest distortion of the shaft in either direction will be transmitted to the ring, resulting in an expansion of the ring and creating a magnetic flux.
TorqStar uses a flux gate magnetometer (FGM) strategically placed around the magnetoelastic ring to measure and convert the magnetic force to an electrical signal. The electrical signal is then relayed to the second part of the electronics package, an amplifier that boosts the signal and transmits it to machine and system controls, display units, or other network controllers. TorqStar enclosures are made to block any outside noise interference - other sources of magnetic force, including machinery and motors, and the earth's magnetic field.
Another critical element of the magnetoelastic/FGM technology is its speed performance, surpassing that of strain gages, and how it affects output consistency and reliability of the process. Typical strain gages provide a response time frequency in the range of 1 msec. Magnetoelastic sensors respond in the frequency of 0.1 msec for instantaneous and seamless reading that helps control the torque and process to tighter tolerance levels.
For process control and monitoring, TorqStar offers consistent, predictable outcome of the operation. The useful life expectancy of cutting tools can be optimized as their torque, increasing with use, can be monitored to accurately predict when wear and dullness will result in a bad part or broken tool. Similarly, in drilling and tapping operations, an incorrect torque reading for either operation may indicate a dull tool or the possibility of a wrong tool size being used.
For more information from Lebow Products, Troy, MI. http://www.lebow-siebe.com
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|Title Annotation:||TorqStar series of noncontact torque sensors from Lebow Products|
|Publication:||Tooling & Production|
|Date:||Jan 1, 1998|
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