GB2218814A - Process and device for measuring a torque applied to a formed member e.g. shaft - Google Patents

Abstract

Torque on a shaft 1 is determined by generating two sets of cyclically-varying measured values (e.g. as represented by triangular waveforms in Figure 3) whose difference is related to the torque which can thus be determined during rotation. A determination can also be effected during torque-loaded stationary conditions of the shaft. The values may be generated by using toothed wheels 2,3 and proximity sensors 5, 6 or, alternatively, annular coded magnetic tapes and co-operating sensing elements. <IMAGE>

Description

PROCESS AND DEVICE FOR MEASURING A TORQUF APPLIED TO A FORMED MEMBER The invention relates to a process and a device for measuring a torque applied to a formed member, especially a shaft, by which a torque-dependent signal is generated.

It is already known to use proximity sensors which cooperate with a sensed element attached to the rotating shaft and by which the displacement in time of the two maxima determined in the course of one rotation serve as a measure for the angle of rotation of the shaft and for determining the resulting torque.

The disadvantage of the prior art processes and devices is that they provide acceptable results only if applied to rotating or rapidly rotating shafts. If the shaft is stationary, no usable signal is generated even if there exists a torque. Such methods and devices cannot be used for machines and devices where even in the stationary condition overloading, for instance during starting, may occur.

It is therefore the object of the invention to propose a process and devices for carrying out the process which generate reliable and evaluatable results both in the case of rotating and at least temporarily stationary shafts in a torque-loaded condition.

The invention provides a process for measuring a torque applied to a formed member, especially a shaft, by which a torque- dependent signal is generated, wherein for generating the signal, two cyclic lines of measured values which change continuously in the course of one rotation are produced in two axially and/or radially spaced regions of the torque-loaded formed member, with the difference between the two measured values determined at the same time being determined as the signal analog to the torque applied.

By producing lines of measured values which are cyclic relative to the rotary motion and measuring the difference between the two measured values determined at the same time, it is possible to obtain evaluatable signals in all operating conditions, i.e. also in the stationary or slowly rotating conditions. However, it is important to select cyclic curves from whose course the angular displacement may be deduced. In a preferred embodiment, two actually identical cyclic lines of measured values are used.

In accordance with the invention, the line of measured values takes the form of a cyclic triangular signal which is dependent on the rotary motion, but it is also possible to generate a sinusoidal signal which is dependent on the rotary motion.

A first device in accordance with the invention for providing a solution and carrying out the process comprises axially and/or radially spaced sensor elements and two sensed elements associated with the formed member, with the sensor elements associated with the formed member being designed as proximity sensors and the sensed elements as toothed discs and with the tooth shape, in respect of distance and overlap in the case of rotation relative to the sensor element, being designed to match the desired cyclic line as a function of the rotary motion. In an alternative embodiment, annular magnetic tapes holding a periodically recurring signal in a coded form are associated with the formed member, with the sensed elements being designed correspondingly for recording the rotary positions of the two tapes.

The process in accordance with the invention will be explained with the help of the device illustrated diagrammatically in the drawings.

In the drawings: Figure 1 shows a measuring device having toothed discs and proximity sensors axially arranged on a shaft representing the formed member; Figure 2 illustrates a toothed disc; Figure 3 is a graph of the values measured by the sensors (sensor voltage) against time at a certain speed; Figure 4 is a graph similar to Figure 3 but showing the measured values at a different speed; and Figure 5 is a detail of a graph similar to Figure 3 or Figure 4 illustrating the value calculation at the inversion points.

The device as illustrated in Figure 1 consists of the shaft 1 whose rotation represents the value for measuring the torque applied. A housing 4 is supported and fixed on the shaft 1. The housing 4 remains stationary even if the shaft 1 therein rotates. On the shaft 1, two axially spaced toothed discs 2, 3 are arranged so as to be non-rotating relative to the shaft.

The two toothed discs 2, 3 are of identical design.

As can be seen from Figure 2, the toothed discs 2, 3 comprise circumferentially distributed teeth 7 separated by gaps 8. The toothed discs 2, 3 are fixed on the shaft 1 in equal phases. In the housing 4, each toothed disc 2, 3 is associated with one of two proximity sensors 5, 6. The two proximity sensors 5, 6 generate a voltage corresponding to the position of approach to a tooth 7.

The shape of the teeth 7 and gaps 8 in respect of their distance from the respective sensor 5, 6 and in respect of their overlap with the sensor 5, 6 is such that in the case of rotation, there exists a cyclic voltage line such as the triangular line illustrated in Figure 3.

Depending on the magnitude of the torque applied, the two toothed discs 2, 3 rotate relative to each other. The position of rotation as determined by the sensors 5, 6 results in two value curves which are displaced relative to each other and whose vertical distance from one another, while being recorded simultaneously, is a measure for the angle of rotation. However, the curve displacement in terms of time is speed-dependent. To eliminate the speed and to be able to make measurments in the stationary condition as well, it is necessary to measure the vertical displacement which is independent of the speed and is determined exclusively by the angle of rotation of the two toothed discs relative to each other.

The difference between the two values measured simultaneously corresponds to the torque applied.

Figure 3 shows the signals for a certain speed with a constant torque.

Figure 4 shows the signals at half the speed, but with the same torque as in Figure 3. In spite of different speeds and thus different time intervals between the signals, the vertical distance and thus the angle of rotation remain the same with the same torque.

These rotation-dependent signals are evaluated by computer.

The voltage values of the two curves M1 and M2 correspond to the input value Mlt and the output value M2t measured by the proximity sensors 5, 6 simultaneously at discreet time intervals.

By taking into account the inversion points in the areas A, C, E, the calculation is carried out using the difference between the two voltage values Mlt and M2t.

The sign is determined by taking into account the sign of the gradients of the curves

Where SGN is the signum or inclination function.

In a simplified method, it is possible to do without the areas B and D because as compared to A, C and E they are very small (given in the figure in a magnified form).

This results in the following calculation specification: M = K (M2 T M1) T where T equals 2 /

with K = adaptation factor (voltage value:torque) M2 - M1 = difference between values measured simultaneously T r sign correction and "fading out" of areas B and D.

With the same gradient sign, T = +1 or -1. The correct sign for M is determined in this way.

With a different sign, T = O, i.e. 1 , in respect of magnitude, T moves towards the value "infinity".

This means that the determined value of M also moves towards "infinity".

If the nagnitude of M is calculated towards the value "infinity", the value is not evaluated, because the signal lines are in the area B or D.

The sign of T evaluates whether both lines are "rising" or "falling". With this calculation it is determined automatically whether the torque applied is positive or negative. This system only uses the linear lines of M1 and M2 and suppresses the regions of transition B and D.

By using a more complex evaluating calculation (see Figure 5) it is also possible to use the areas B and D for measuring purposes. For this purpose, the line M is modified in the area of transition in such a way that a calculation becomes possible by subtraction of the two values M1 and M2 and by an additional sign-determining term.

For the purpose of this calculation and during the transition from the areas A and C into areas B and D, the last value of M2 has to be stored in area A and C respectively in the evaluation unit.

Now a value M2X is introduced for which the following applies: if SGN

M2 equals the actual value M2X . .

Upon the first occurrence of SGN dM1 not being equal to SGN dM2 , dt dt the value M2X = M1t (M2 at time t) is retained.

Only when SGN

as the continuously changing value, becomes equal to M2 . For the purpose of the calculation it is assumed that SGN (o) = 1.

M = K (M2 + R - Mi) X S where R = 2 (M 2X - M 2) and S = SGN (|M2 |-| M2X|) SGN dM2 dt with R = correction of value M2 for the calculation in the areas of transition B, D S = definition of sign.

This equation applies to the entire area (A,B,C,D,E,...).

The correction of value M2 by value R is illustrated in Figure 5.

Claims (9)

1. A process for measuring a torque applied to a formed member, especially a shaft, by which a torquedependent signal is generated, wherein for generating the signal, two cyclic lines of measured values which change continuously in the course of one rotation are produced in two axially and/or radially spaced regions of the torque-loaded formed member, with the difference between the two measured values determined at the same time being determined as the signal analog to the torque applied.

2. A process according to Claim 1, wherein the two lines of measured values are actually identical.

3. A process according to either one of Claims 1 and 2, wherein a cyclical triangular signal which is dependent on the rotary motion is generated to represent the line of measured values.

4. A process according to either one of Claims 1 and 2, wherein a sinusoidal signal which is dependent on the rotary motion is generated to represent the line of measured values.

5. A device for carrying out the process according to any one of Claims 1 to 4, comprising two sensor elements and two sensed elements associated with the formed member on which the applied torque has to be measured, the sensor elements being spaced at an axial and/or a radial distance, wherein the sensor elements associated with the formed member are proximity sensors and the sensed elements are toothed discs and in respect of distance and overlap in the case of rotation relative to the sensor element, the shape of the teeth of the discs is designed to match the desired cyclic line as a function of the rotary motion.

6. A device for carrying out the process according to any one of Claims 1 to 4, wherein annular magnetic tapes holding a periodically recurring signal in a coded form are associated with the formed member, and sensing elements are designed correspondingly for recording the rotary positions of the two tapes.

7. A device according to either one of Claims 5 and 6, wherein the shaft is itself the formed member.

8. A process for measuring a torque substantially as hereinbefore described with reference to the accompanying drawings.

9. A device for measuring a torque substantially as hereinbefore described with reference to and as shown in the accompanying drawings.