GB2527819A

GB2527819A - Rotation transducer

Info

Publication number: GB2527819A
Application number: GB1411877.2A
Authority: GB
Inventors: Michael Baker
Original assignee: Moog Controls Ltd
Current assignee: Moog Controls Ltd
Priority date: 2014-07-03
Filing date: 2014-07-03
Publication date: 2016-01-06
Also published as: GB201411877D0

Abstract

A rotation transducer 100 to measure turn count and angle of rotation, and a method to measure rotation of a shaft 114. The rotation transducer has two rotating members, the second 106 driven by the first 104. Each member is configured to rotate at a different rate, therefore out of phase (figure 2), and each has an associated sensor 108, 110 to measure its position. A controller 132 reads signals from the position sensors to determine the phase difference between the first and second members, and consequently the number of turns made by the first member. The phase difference may be calculated by subtracting the first sensor reading from the second. The controller may calculate the phase difference at a predetermined position of the first member. The first and second members may be gears with a different number of teeth, be in direct contact with each other, or connected with a belt, a chain or another gear. The position sensors may be magnetic or optical. A further first and second sensor, with further controller may be included to provide an additional measure of number of turns of the first member.

Description

Rotation transducer The present invention is concerned with a rotation transducer. More specifically, the present invention is concerned with a shaft count and rotational position transducer for non-volatile shaft count and accurate measurement of shaft position.

Measurement of shalt count and degree or rotation is desirable in a wide range of technical fields. For examp'e, in the aircraft control surface actuation field the high lift system (HLS) comprises a drive shaft extending along each wing. These shafts are configured to deploy the high lift surfaces (slats and flaps) to adjust the aerodynamic properties of the wing in flight. It is very important that the shafts deploy simultaneously, as unequal aerodynamic properties can detrimentally affect the aircraft's flight. As such. transduccrs arc used to measure the shaft count and position of each shaft. It can therefore be confirmed that the shafts are rotating in unison.

In the HLS field in particular. the requirement is that the sensor must be able to mcasurc a shaft count of up to 160 turns and angular position in ally givcn turn to an accuracy of 20 degrees. This requirement is typical of other technical fields. The sensor must also he non-vo'atile (i.e. its position and count must he absolute), because in the event of interruption ol the electrica' supply, any electronic shalt count system may he inadvertently reset. A resolver or RVDT simply attached directly to the shaft would be volatile because it would require an attached electronic memory of some description to "remember" how many turns have been made (only the angular position of the shaft in the present turn would be non-volatile). Prior art solutions involve the usc of a gearbox to convert the range of motion of the shaft (many turns) into a single turn of the transducer. This is achieved by using a gearbox between the shaft and the resolver or RVDT. The gearbox will reduce the movemeni ol the shall hy (in the above example) over 160:1 and as such the entire range of movement can he detected within a single turn of thc rcsolvcr or RVDT, making thc systcm non-volatilc.

Evidently the gearbox adds cost and complexity to the system, and the model of resolver or RVDT which can measure to the required degree at the output to the gearbox is expensive. Further, gearhoxes can add e.g. backlash which reduces accuracy. Further, two devices are required if redundancy is needed (e.g. in aircraft applications) which adds further complexity and cost.

What is required is an inexpensive and robust non-volatile means of measuring the S position of a shaft through a high number of turns to a high degree of accuracy.

It is the aim of the present invention to provide such a device.

According to a first aspect of the invention there is provided a rotation transducer comprising: a first rotating member: a second rotating member configured to be driven by the first rotating member; a first sensor arranged to sense a position of the first rotating member; and, a second sensor arranged to sense a position of the second rotaling member; in which the first and second rotating members are configured to rotate out of phase; a controller configured to read and process readings from the first and second sensor; which controller is configured to determine the number of turns undergone by the first member by using the readings from the first and second sensors to determine the phase difference between the first and second members.

Advantageously, the present invention provides a non-volatile position transducer for a rotational input connected to the first member. The transducer can both count turns (by determining phase difference) and sense the absolute position of the input (by interrogating the first sensor). Therefore, unlike prior art systems which require a gearbox and a highly sensitive sensor to eliminate volatility, the present invention requires no gearbox (other than the first and second members) and two relatively low sensitivity sensors.

For a prior art system requiring an accuracy of N degrees over M turns, the resolver or RVDT would require a resolution of 1/NxM. hi the present invention, with the two members having a phase lag of 1/M, two sensors having a resolution of N/360 is sufficient. This results in a much lighter, robust, and simpler system.

Furthermore, because the second member is unloaded, reliability of the transducer is S high. There is little or no backlash, and wear between the members is very low.

Preferably the first and second members are gears having an unequal number of teeth.

Advantageously this gives a consistent and predictable phase difference, and because the second member is unloaded results in a reliable transducer. Preferably the first member has T teeth and the second member has T+1 or T-1 teeth.

The first and / or second sensors may bc magnetic position sensors configured to read a magnetic pattern on the first and / or second member respectively. Alternatively the first and / or second sensors are optical position sensors configured to read an optical IS pattern on (lie first and / or second member respectively. In both cases, die use of "non-contact" sensors increases the reliability of the transducer as both members are not thaded by the sensors.

Preferably the first and second members are in direct engagement. This produces a compact and robust system.

Alternatively, the first and second members may be in indirect engagement via an intermediate drive arrangement.

For example. the first and second members are gears, and the intermediate drive arrangement comprises at least one intermediate gear engaged with the first and second members. This reduces the amount of phase difference still further, advantageously making a transducer which can detect an even higher number of turns.

The intermediate drive arrangement may comprise at least one flexible member engaged with the first and second member. The flexible member may he a belt or chain.

Preferably the controller is configured to determine the phase difference from the reading from the second sensor at a predetermined position of the first member sensed by the Iirst sensor. Alternatively the controller is configured to determine the phase difference by subtracting the reading from the first sensor from the reading from the S second sensor.

The transducer may comprise a further first sensor arranged to sense a position of the first rotating member; and, a further second sensor arranged to sense a position of the second rotating member, for redundancy. As such, the transducer may comprise a further controller configured to read and process readings from the further first and further second sensor; which further controfler is configured to determine the number of turns undergone by the first member by using the readings from the further first and further second sensors to deternñne the phase difference between the first and second members.

According to a second aspect of the invention there is provided a method of measuring the rotation of a shalt comprising the steps of: providing a first rotating member; providing a second rotating member configured to he driven by the first rotating member; in which the first and second rotating members are configured to rotate out of phase; providing a first sensor arranged to sense a position of the first rotating member; and, providing a second sensor arranged to sense a position of the second rotating member; connecting a shaft to be measured to the first rotating member; and.

determining the number of turns undergone by the shaft by determining the phase difference between the first and second members using readings from the first and second sensors.

A rotation transducer according to the present invention will now be described with reference to the accompanying figures in which: Figures 1 shows a first rotation transducer according to the present invention; Figures 2a to 2j show part of the transducer of Figure 1 in a variety of angular positions throughout a single rotation; and, Figures 3a to 3c shows sensor readings from the transducer of Figure 1 throughout several rotations.

Turning to Figure 1, a transducer 100 comprises a housing 102, a first rotating member 104 and a second rotating member 106. Each rotating member 104, 106 comprises a sensor 108, 110 proximate thereto.

The first rotating member 104 is a spur gear comprising a disc 112 mountcd on a shaft 114 for rotation about an axis Xl. and a set of 9 radially projecting teeth 116 extending from the disc 112. The teeth 116 are not shown in Figure 1. but are visible in Figures 2a to 2j.

The second rotating member 106 is a spur gear comprising a disc 118 mounted on a shalt 120 for rotation about an axis X2, and a set of 10 radially projecting teeth 122 extending from the disc 118. The teeth 122 arc not shown in Figure 1, but arc visible in Figures 2a to 2j.

Each rotating member 104, 106 has a magnetic code 124. 126 applied to an annular region of the discs 112, 118 rcspcctivdy. Each code 124, 126 comprises a plurality of radially extending magnetic lines laser wnttcn into thc material of thc respective member 104, 106. During manufacture, a laser changes (very locally) the magnetic properties of the subject material. The lines are uneven-they vary in thickness and separation to the extent that the absolute position of the member 104, 106 can be determined by reading a series of adjacent lines. The magnetic code is "pseudo-random'.

The first sensor 108 is configured to sense the magnetic properties of the first rotating member 104. The second sensor 110 is configured to sense the magnetic properties of the second rotating member 106. Both sensors 108, 110 are connected via respective data links 128, 130 to a micro-controller 132. Before use, the sensors 108, 110 and microcontroller 132 are calibrated to learn the pseudo-random pattern of the codes 124, 126 and thereby detect the absolute position of the members 104, 106. The microcontroller can report the absolute rotational position of each member using data S from the sensors 108. 110.

The first and second rotating members 104, 106 are meshed as shown in Figures 2a to 2j such that rotation of the first rotating member drives rotation of the second rotating member. The shaft 114 is driven by the member for which rotation is to be measured (for example a direct drive from the drive shaft of an aircraft high lift system). The shaft 120 is simply present to support rotation of the second rotating member 106, and is not externally connected (making the second rotating member 106 a vernier gear in this embodiment).

Turing to Figures 2a to 2j, the operation of the transducer 100 is described in more detail. Throughout Figures 2a to 2j. one tooth (labelled as 116' and 122') is shaded to provide an indication of the degree of rotation.

Moving from Figure 2a to 2j, the first member 104 undergoes a 360 degree rotation about axis Xl in a clockwise direction. Because the first member 104 is drivingly connected to the second member 106. the second member 106 also rotates. Because the second member 106 has one tooth more than the first member 104, the second member rotates by 9/10 of the rotation of the first member (i.e. 324 degrees).

The second member 106 is therefore out of phase with the first member. If clockwise rotation of the first member continues, the first and second members 104. 106 would not both return to the position of Figure 2a until 10 turns of the first member 104.

Turning to Figures 3a and 3h. the output from the microcontroller 132 is shown on the Y axis for a series of 9 360 degree tunis of the first member 104. The Y axis represents the amount of rotation the respective member has undergone, assuming a resolution of 1/10 of a revolution (36 degrees). For Figure 3a, the graph represents a data signal S 108 from the microcontroller 132 indicative of the degree of rotation of the first member 104, and for Figure 3b, the graph represents a data signal 5110 from the microcontroller 132 indicative of the degree of rotation of the second member 106.

In each case, the signals S 108, SI 10 climb with rotation in 36 degree increments until returning to zero after a full revolution. The amount of rotation of the input shaft 114 S (and hence the first member 104) is visible on the X-axis of Figures 3a to 3b. with each vertical dashed line representing one turn.

As can be seen in Figure 3a, for each turn of the first member the signal S108 from the microcontroller 132 reports a full rotation from the first sensor 108. Similarly for Figure 3b, the signal 5110 from the microcontroller 132 reports the rotation of the second member 106 hut with a phase lag compared to the first member. In other words because the second member 106 rotates more slowly than the first member 104 (on account of the second member 106 having more teeth), the sensor 110 detects a full revolution progressively later than the sensor 108. This phase difference results in the signals S108, S110 showing 9 rotations of the second member 106 for 10 rotations of the first member 104 (it will be noted that only 9 peaks of signal S108 and 8 peaks of signal SI 10 are visible in Figures 3a and 3h).

Figure 3c is representative of the phase lag of the second member 106 compared to the first member 104, and is measured when the first member 104 is at top dead centre (TDC-i.e. at. the position shown in Figure 2a). The phase lag PL is the signal Sll0 when the first member 104 passes TDC (i.e. when S108 drops from maAimum to zero). At the position shown in Figure 2a, the phase lag of the second member 106 is it its maximum (at time zero in this example, signal SilO represents a full rotation of the second member 106 has just occured). After the first rotation of the first member (referring to Figure 2j) the second member 106 has rotated less than ihe first member 104. As such, the recorded phase lag PL has decreased. This continues throughout 10 turns of the first member 104 at which point the members 104, 106 are in phase before the phase lag PL jumps hack to the maximum.

The signals S108 and 5110, and the phase lag PL can he used to measure the turn count and absolute position of the input connected to the shaft 114. The transducer can determine the number of turns that the shaft has undergone (between 0 and 10) by examining the phase lag PL. which is indicative of the number of revolutions of the shaft 114. The absolute position of the shaft 114 within that revolution can be determined by examining the signal S108. Even in the event of an electrica' intcimption to the micro-controller 132, when operation resumes, the phase lag of the S second member 106 and the absolute position of the first member 104 are not affected.

The phase lag can be deteimined by reviewing the absolute positions of the two members. As such, the transducer is non-volatile.

The above example is capable of sensing up to 10 turns at an accuracy of 36 degrees (the resolution of the signal S 108 is 1/10 turn). Therefore two relatively inexpensive sensors can produce an overall accuracy of 1/100 in a non-vcAatilc manner. A prior art system would use a gearbox on the shaft to reduce the rotation by 10:1 (to make the system non-volatile by limiting the range of motion of the sensor to one rotation) and would therefore require at least one much more expensive and delicate resolver or RVDT with all accuracy of 3.6 degrees.

It is noted that in the above example. the phase lag is measured at TDC of the first member 104, hut this does not need to he the case. It is envisaged that the phase lag PL could he calculated by the microcontroller 132 at any position of the first member 104.

For the example discussed in the introduction, for 160 turn 20 degree resolution, a gearbox driven resolver or transducer with an accuracy of 1/3200 would he required.

With the present invention, a first gear with 160 teeth, and a second with 159 would be required, with two sensors having an accuracy of 1/18 of a turn (20 degrees).

Variations fall within the scope of the present invention.

The members 104, 106 have the ability to accommodate further sensors. For example.

in one embodiment a second set of sensors are positioned diametricafly opposite the first set 108, 110. The second set arc connected to a separate micro-controller for redundancy.

Other types of sensors could be used to detect rotation of the members 104, 106. For example, resolvers, potentiometers or RVDTs could be mechanically coupled to the members 104, 106. Optical sensors could he used to detect a pattern on the members 104, 106. Potentiometers could also be used.

The first and second member may be connected in alternative manners to provide the required phase lag. For example: * The second member may have a lower number of teeth than the first member.

This would still produce a detectable phase lag (but the second member would rotate faster than the first, creating a "reverse lag" or phase advance).

* The first and second members 104, 106 may he rollers having a different diameter. The rollers would he frictionally coupled.

* An intermediate member or drive transfer means may he provided between the first and second member. For example: o A belt drive may extend between two spaced apart first and second members. The belt may he a smooth belt, or a timing (toothed) belt; o A chain may extend between two spaced apart first and second members having different numbers of teeth; o A drive train comprising one or more inteimediate gears or rollers may he provided being engaged with the first and second members to transfer rotation. This would further gear movement of the second member, which would significantly increase the number of turns which the transducer can count, as the phase lag would be made even smaller.

o A rack may he provided being simultaneously engaged by the first and second members.

Claims

Claims 1. A rotation transducer comprising: a first rotating member: a second rotating member configured to be driven by the first rotating member; a first sensor arranged to sense a position of (lie first rotating member; and, a second sensor arranged to sense a position oldie second rotating member; in which the first and second rotating members are configured to rotate out of phase; a controller configured to read and process readings from the first and second sensor; which controller is configured to determine the number of turns undergone by the first member by using the readings from the first and second sensors to determine the phase difference between the first and second members.
2. A rotation transducer according to claim 1, in which the first and second members are gears having an unequal number of teeth.
3. A rotation transducer according to claim 2, in which the first member has T teeth and the second member has T+l orT-l teeth.
4. A rotation transducer according to any preceding claim, in which the first and I or second sensors are magnetic position sensors configured to read a magnetic pattern on the first and / or second member respectively.
5. A rolalion lransducer according to ally ol claims 1 to 3. in which the lirsi anti I or second sensors are optical position sensors configured to read an optical pattern on the first and I or second member respectively.
6. A rotation transducer according to any preceding claim, in which the first and second members are in direct engagement.
7. A rotation transducer according to any of claims 1 to 5, in which the first and second members are in indirect, engagement via an intermediate drive arrangement.
8. A rotation transducer according to claim 7, in which the first and second members are gears. and the intermediate drive arrangement comprises at least one intermediate gear engaged with the first and second members.
9. A rotation transducer according to claim 7, in which the intermediate drive arrangement comprises at least one flexible member engaged with the first and second member.
10. A rotation transducer according to claim 9. in which the flexible member is a belt or chain.12. A rotation transducer according to any preceding claim in which the controller is configured to determine the phase difference from the reading from the second sensor at a predetermined position of the first member sensed by the Iirst sensor.13. A rotation transducer according to any of claims I to 11 in which the controller is configured to determine the phase difference by subtracting the reading from the first sensor from the reading from the second sensor.14. A rotation transducer according to any preceding claim comprising: a further first sensor arranged to sense a position of the first rotating member; and.a further second sensor arranged to sense a position of the second rotating member.15. A rotation transducer according to claim 14 comprising: a further controller configured to read and process readings from the further first and further second sensor; which further controller is configured to determine the number of turns undergone by the first member by using the readings from the further first and further second sensors to determine the phase difference between the first and second members.16. A method of measuring the rotation of a shaft comprising the steps of: S providing a first rotating member; providing a second rotating member configured to be driven by the first rotating member; in which the first and second rotating members are configured to rotate out of phase; providing a first sensor arranged to sense a position of the first rotating member; and, providing a second sensor arranged to sense a position of the second rotating member; connecting a shaft to be measured to the first rotating member; and, determining the number ol (urns undergone by the shaft by determining (he phase difference between the first and second members using readings from the first and second sensors.17. A rotation transducer and a method of measuring as described herein, with reference to, or in accordance with, the accompanying drawings.