Method for measuring torque using angle sensors – ifm

It is difficult to measure torque on a rolling shaft, and there are several ways to do it. The most common method is to derive the torque from the energy required by the rolling shaft. In general, this means measuring the current of the motor that drives the rolling shaft. This is sketchy but inaccurate, as the current consumption is related to other factors such as speed, supply voltage, bearing condition, and temperature.

A more accurate approach would be to use strain gauges to measure the deformation on the shaft, perhaps using a surface acoustic wave (SAW) device. While this method is accurate, it requires either a sliding ring or a wireless method to transmit the strain gauges on the shaft to the outside world.

Method for measuring torque using angle sensors – ifm

Method for measuring torque using angle sensors – ifm

Strain gauges often have a large temperature coefficient and have a poor habit of loosening in harsh situations. Measuring torque in the test chamber with strain gauges or SAW devices is generally fine, but it is not suitable for many industrial applications.

The torque of the engine is measured by changing, so that the torque on the shaft is measured by measuring the phase displacement between two "multi-speed" resolvers mounted on the shaft and kept in a straight line with the shaft. Following the rolling of the shaft, two signals are generated per resolver, one in a sinusoidal curve and the other in a cosine curve.

If the loaded torque is zero, the signal from the two resolvers appears to have zero phase displacement. With the loading torque, it appears that the phase of one output signal is displaced in relation to the other. The phase displacement and the loaded torque are directly shared. If a multi-speed resolver is used with a large number of cycles, only a small change is required to cause significant phase shifts.

This makes this skill very sensitive and suitable for measuring changes in less than 1 degree or even less than 0.1 degrees. Two resolvers (one inside the other) can be placed on a special flexible shaft or concentrically and the inside and outside of the shaft can be connected by a strong torsional tension spring.

With the development of sensor skills, more and more resolvers will be replaced by increasingly modern inductive encoder solutions. Inductive encoders operate on the same inductive principle as resolvers, but they use a printed circuit board instead of a wire-wound transformer structure. This is important to help minimize the size, weight and cost of inductive encoders, together with maximizing their measurement performance. In addition, the inductive encoders offer an easy-to-use electrical interface – a DC power input and a serial data output.

Because inductive encoders are designed with the same underlying physical properties as resolvers, they offer the same operational advantages. They are flat and have a large hole in the middle, like a resolver, without the need for a slip ring. Inductive encoders can be used to measure torque and affirm viewpoints.

Because all the electronic components of the inductive encoder are already in its stator, there is no need to specify and supply the electronic components separately. The inductive encoder is also capable of supplying up to 4 million counts per revolution, so that even a small change in viewpoint can be used to achieve a very high resolution torque measurement. The thermal coefficient of an inductive encoder is smaller than that obtained by strain gauge placement. Any dynamic distortion due to the high angular velocity of the shaft can be eliminated when the same clock signal is used to trigger the readings of both encoders.

With inductive encoders, there is no risk of damage to the equipment in the event of overloading or torque shocks. This skill also offers two types of measurement – viewpoint and torque, which are less expensive than measuring torque with strain gauges. Measuring torque with viewpoint sensors may be an old skill, but with the participation of modern inductive encoders, the use of sensing physics for viewpoint measurement has been revitalized, and this method of sensing torque and viewpoint is also very useful.

Method for measuring torque using angle sensors – ifm

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