GB2107880A

GB2107880A - Torque measuring

Info

Publication number: GB2107880A
Application number: GB08226686A
Authority: GB
Inventors: Iv John Simpson League
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1981-10-13
Filing date: 1982-09-20
Publication date: 1983-05-05
Also published as: FR2514500B1; JPS5875039A; SE8204912D0; BE893972A; IN156682B; IT8223721A0; SE8204912L; DE3235122A1; GB2107880B; NL8203122A; FR2514500A1; IT1153232B

Abstract

Disclosed are a non-contact method and apparatus for measuring the torque of a rotating shaft. Four non-contact proximity magnetic sensors (A, B, C and D) in a horizontal plane are used on the outside of a coupling spacer (32) connecting rotating shafts (20, 22) and having symmetrical dotted patterns (34, 36). Their signals are translated into a measurement of torque. Two of the sensors (A, C) are at one end of the spacer, diametrically opposite each other relative to the centre-line of one shaft (20), and the other two (B, D) are at the other end of the spacer, diametrically opposite each other relative to the centre-line of the other shaft (22). Horizontal and vertical centre-line displacements of the coupling are compensated for without the need of adding corrective signals to or rebiasing sensing circuitry. <IMAGE>

Description

SPECIFICATION Torque measuring The present invention relates to torque measuring and more particularly to a method and apparatus for the non-contact measurement of the torque of a shaft.

By measuring the torque of a rotating shaft of a coupling between driving and driven equipment it is possible to calculate the efficiency of the equipment during operation. Such readings can also be used to detect power surges in such equipment and notify operators of necessary changes in operating conditions before such surges can damage the driving or driven equipment. Further, the readings can be used to determine when maintenance is necessary.

The prior art has attempted to measure such torque by various methods. One such attempt proposes a device wherein an additional sleeve is fitted on the coupling to compensate for movement of the coupling. While this has produced satisfactory measurement of torque, the additional sleeve tends to raise the price of the coupling and also increases the weight of the coupling. Strain gauges using slip rings have also been used, but these tend to wear out quickly and require frequent replacement if they are to be relied upon for accurate measurements. It has also been proposed to place a signal transmitter inside the coupling. However, since couplings do not operate in ideal environments, frequently the transmitters would fail, necessitating shutting down the equipment and disassembling the coupling to replake the transmitter. This results in expensive downtime.

According to the present invention from one aspect, there is provided apparatus for measuring the torque of a rotating shaft, the apparatus comprising: (a) a slotted pattern around the said shaft to rotate therewith; (b) a plurality of non-contact pick-ups mounted in a horizontal plane and in close proximity to and on opposite sides of said slotted pattern relative to the centre-line of the said shaft, said pick-ups being adapted to provide signals resulting from rotation of the slotted pattern with the said shaft; (c) circuit means for analysing the said signals and translating said signals into a signal representing the torque of the said shaft; and (d) means for displaying said torque signal as a direct measure of the torque.

According to the present invention from another aspect, there is provided a method for measuring the torque of a rotating shaft using a non-contact sensor which senses rotation of the shaft to produce an alternating signal dependent on such rotation, which method includes the step of producing from the said signal a further signal dependent on such rotation by sensing zero crossover points of the first-mentioned signal to substantially compensate for centre-line movement in a horizontal direction of the said shaft.

According to the present invention from another aspect, there is provided a method for measuring the torque of a rotating shaft using first and second non-contact sensors on respective sides of a coupling which includes the said shaft to produce first and second cyclically varying signals each dependent on the rotation of the shaft, in which method the said signals are combined to substantially cancel equal and opposite phase shifts thereof due to movement of the centre-line of the said shaft in a vertical direction to produce a signal in which such movement is substantially compensated for.

According to the present invention from another aspect, there is provided a method for measuring the torque of a rotating shaft, the method comprising the steps of: (a) providing a slotted pattern around the said shaft which rotates therewith; (b) sensing signals generated from the rotation of the said pattern by means of passive, noncontact pick-ups; and (c) analysing the said signals to transform them to a measure of the said torque.

The present invention will now be described, by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial plan view in section of a coupling Figure 2 is a block diagram of sensor circuitry associated with the coupling; Figure 3 is a schematic diagram of the sensor circuitry; Figure 4 shows waveforms occurring in the sensor circuitry; and Figure 5 is a graphic representation of the automatic compensation for centre-line movement of the coupling which the sensor circuitry provides.

Referring to Figure 1, a coupling generally designated 10 comprises hubs 12 and 14 having outwardly extending gear teeth 1 6 and 1 8 respectively. Hubs 12 and 14 are respectively mounted on a driving shaft 20 and a driven shaft 22 by conventional means such as keyways, not shown. Operably engaging the outwardly extending gear teeth 1 6 and 18 respectively of hubs 12 and 14 are outwardly extending gear teeth 24 and 26 respectively of sleeves 28 and 30 respectively. Sleeves 28 and 30 are operably connected by a spacer 32 by conventional means such as bolts, not shown. The twist produced in the spacer 32 between the sleeves 28 and 30 is in direct proportion to the torque transmitted from the driving shaft 20 to the driven shaft 22.

Error signals caused by shaft centre-line movement in the horizontal and/or vertical direction also appear as torque signals and must be eliminated to obtain a true torque value.

As shown in Figure 1, two symmetrical slotted patterns 34 and 36 are cut into the surface of spacer 32 and extend circumferentially around the outside surface of spacer 32. Each slotted pattern comprises 65 teeth on a pitch diameter of 20.64 cm.

Mounted in a substantially horizontal plane are four passive magnetic pick-ups A B, C and D, the pick-ups A and C being in close proximity to the pattern 34 and the pick-ups B and D being in close proximity to the pattern 36. The pick-ups A C and B, D are approximately 1.5 mm from the slotted patterns 34 and 36 respectively. Mounting can be in any conventional manner, such as a cylinder to encircle the outside of spacer 32.

Rotation of spacer 32 causes slotted patterns 34 and 36 to induce an A-C signal in each of passive magnetic pick-ups A C and B, D. Each probe signal is increased by a respective amplifier 38 of a respective probe circuit 42 (see Figure 3).

It is to be understood that each pick-up has an identical probe circuit 40 to that shown for A in Figure 3. In each case, the amplified signal is transmitted to a voltage comparator 42 of the probe circuit 40. The output of each comparator 42 is a square-wave signal which switches at the identical zero crossover point as the A-C signal from the respective pick-up, the signals from pickups B, C and D being likewise amplified and shaped.The square wave signal from each comparator 42 is then fed to a respective diode 43 where the bottom portion is clipped off, the output voltage being reduced to a lower operating level through a respective voltage divider comprising resistors R1 and R2, the output points of the probe A, B, C and D circuits at the respective voltage dividers being designated Al, Bi, Cl and Dl. NAND gates 54 and 55 acting as inverters serve to change the phases of the signals from points Al and C1 of the probe A and probe C circuits respectively, as is seen in the timing diagram of Figure 4.The signal from gate 54 and the signal from the point B1 of the probe B circuit are combined in a NAND gate 44 and the signal from gate 55 and the signal from the point D1 of the probe D circuit are combined in a NAND gate 46, buffer circuits 50 to 53 providing signal conditioning which serves to isolate and protect the low level logic gates 54, 44, 55 and 46.

The combined signals from probes A and B output from gate 44 and the combined signals from probes C and D output from gate 46 and fed to a NAND gate 48. The output of gate 48 is shown in the timing diagram before any vertical shift has occurred as signal E of Figure 4. The same output is shown as signal El of Figure 4 after a vertical shift has occurred at the driven or load end of the spacer shaft 32. Note that the average value of the waveform E is equal to the average value of the waveform El for 360 electrical degrees of rotation, that is, for one full tooth rotation. Thus, it can be seen that the error caused by vertical shaft movement at the driven end has been cancelled or eliminated. This is also true for vertical shaft movement at the drive end.

The output of gate 48 is a signal which has had any component induced by horizontal or vertical movement of the coupling centre-line eliminated, and is a signal convertible to the true torque applied to the coupling. Such conversion can be accomplished in conventional signal averaging circuitry such as shown in Figure 3.

Movement of the coupling centre-line in a horizontal direction will cause the amplitude of each induced A--C signal to vary as is shown in Figure 5. These amplitude variations will cause the phase of the output signal to vary if compensation is not provided. Only the zero cross-over point of the A--C signal remains the same since the operating frequency remains the same. Each voltage comparator 42, Figure 3, functions as a zero cross-over detector and a pulse converter to translate the A-C signal produced by the respective probe into a squarewave signal directly proportional to the frequency or angular rotation of the spacer 32.

Referring to Figure 5, any ascending vertical movement of the shaft 20 will cause the A-C signal induced in sensor probe A to be phase shifted in a positive or leading direction for clockwise rotation of the shaft. Conversely, the identical signal induced in sensor probe C mounted diametrically opposite probe A will be shifted in phase in a negative or lagging direction.

This phase lead at probe A exactly equals the phase lag at probe C in magnitude and when these two signals are combined in NAND gate 48, the positive and negative phase shifts cancel. This phenomenon also occurs between probe B and probe D when shaft 22 ascends or descends in the vertical direction. The unwanted error signal caused by vertical centre-line movement is therefore eliminated and the true torque signal directly proportional to shaft twist remains.

Claims

1. Apparatus for measuring the torque of a rotating shaft, the apparatus comprising: (a) a slotted pattern around the said shaft to rotate therewith; (b) a plurality of non-contact pick-ups mounted in a horizontal plane and in close promixityto and on opposite sides of said slotted pattern relative to the centre-line of the said shaft, said pick-ups being adapted to provide signals resulting from rotation of the slotted pattern with the said shaft; (c) circuit means for analysing the said signals and translating said signals into a signal representing the torque of the said shaft; and (e) means for dispiaying said torque signal as a direct measure of the torque.

2. Apparatus according to claim 1 , wherein there is another shaft with which the firstmentioned shaft is coupled, there being another such slotted pattern around the other shaft to rotate therewith and a further plurality of such non-contact pick-ups mounted in a horizontal plane and in close proximity to and on opposite sides of the said other slotted pattern relative to the centre-line of the said other shaft the said circuit means being arranged for analysing the signals provided by the said other pick-ups in producing the said torque signal.

3. Apparatus according to claim 1 or 2, wherein the or each slotted pattern comprises a plurality of teeth.

4. A method for measuring the torqe of a rotating shaft using a non-contact sensor which senses rotation of the shaft to produce an alternating signal dependent on such rotation, which method includes the step of producing from the said signal a further signal dependent on such rotation by sensing zero cross-over points of the first-mentioned signal to substantially compensate for center-line movement in a horizontal direction of the shaft.

5. A method according to claim 4, wherein the shaft is in a coupling, being coupled to another shaft with a coupling spacer between the shafts, there being another such sensor which senses rotation of the other shaft to produce another alternating signal, dependent on the rotation of the other shaft, which method includes the step of producing from the said other signal another further signal dependent on rotation of the said other shaft by sensing zero cross-over points of the said other alternating signal to substantially compensate for centre-line movement in a horizontal direction of the said other shaft.

6. A method for measuring the torque of a rotating shaft using first and second non-contact sensors on respective sides of a coupling which includes the said shaft to produce first and second cyclically varying signals each dependent on the rotation of the shaft, in which method the said signals are combined to substantially cancel equal and opposite phase shifts thereof due to movement of the centre-line of the said shaft in a vertical direction to produce a signal in which such movement is substantially compensated for.

7. A method according to claim 6, wherein the said shaft is in a coupling, being coupled to another shaft with a coupling spacer between the shafts, there being third and fourth such sensors on respective sides of the coupling to produce third and fourth cyclically varying signals each dependent on the rotation of the said other shaft, in which method the third and fourth signals are combined to substantially cancel equal and opposite phase shifts thereof due to movement of the centre-line of the said other shaft in a vertical direction to produce a signal in which such moment is substantially compensated for.

8. A method for measuring the torque of a rotating shaft, the method comprising the steps of: (a) providing a slotted pattern around the said shaft which rotates therewith; (b) sensing signals generated from the rotation of the said pattern by means of passive, noncontact pick-ups and (c) analysing the said signals to transform them to a measure of the said torque.

9. Apparatus for measuring the torque of a rotating shaft, substantially as herein described with reference to the accompanying drawings.

10. A method for measuring the torque of a rotating shaft, substantially as herein described with reference to the accompanying drawings.