WO2005010464A1

WO2005010464A1 - Method and device for movement sensing

Info

Publication number: WO2005010464A1
Application number: PCT/IB2004/002354
Authority: WO
Inventors: John Laddier De Villiers
Original assignee: Technology Finance Corporation (Pty) Ltd
Priority date: 2003-07-25
Filing date: 2004-07-22
Publication date: 2005-02-03

Abstract

A sensor (12) for sensing movement of a movable member (18) along a movement path (20), the sensor (12) including at least one transducer (24) located in proximity to a possible movement path of the member (18), the transducer (24) being connected in a loop circuit (30). The sensor (12) also includes a signal generator connected to the loop circuit (30), the signal generator being operable to generate a signal in the loop circuit (30) at a frequency which is associated with the characteristics of the transducer (24). The frequency of the loop circuit (30) is variable as a result of a change in the characteristics of the transducer (24) caused by variation in the relative positioning of the member (18) and the transducer (24). The sensor (12) further includes a detection circuit (36) for detecting variation in the frequency of the loop circuit (30).

Description

METHOD AND DEVICE FOR MOVEMENT SENSING

THIS INVENTION relates to movement sensing. More particularly, it relates to a sensor, a sensing arrangement, a braking arrangement and a vehicle. According to the invention, there is provided a sensor for sensing movement of a movable member along a movement path, the sensor including at least one transducer located in proximity to a possible movement path of the member, the transducer being connected in a loop circuit; a signal generator connected to the loop circuit, the signal generator being operable to generate a signal in the loop circuit at a frequency which is associated with the characteristics of the transducer, the frequency of the loop circuit being variable as a result of a change in the characteristics of the transducer caused by variation in the relative positioning of the member and the transducer; and a detection circuit for detecting variation in the frequency of the loop circuit.

When the sensor has more than one transducer, it may include a separate signal generator for each loop circuit. The transducers may then be located in spaced relationship along the movement path, but could also be arranged in abutting relationship.

The transducer may include an inductive element having the characteristic that its inductance changes depending on the relative positioning of the movable member and the transducer. In another embodiment, the transducer may include a capacitive element having the characteristic, that its capacitance changes depending on the relative positioning of the movable member and the transducer. The detection circuit may include a phase-locked loop associated with each loop circuit, the phase-locked loop being operable to detect a change in the frequency of the loop circuit.

The sensor may further include a processor, operable to receive a signal from one or more phase-locked loops when the frequency of the loop circuit changes and, in response, operable to calculate any one of the speed- and direction of movement of the member based on any one of the frequency change, the order- and the interval of the received signals. The movable member may move along a linear movement path. In another embodiment, it may move along an arcuate path, e.g. it may be in the form of a rotor rotating in a constant plane, or helically split washer fashion. It may also be in the form of an off-centre disk on a rotor moving along an eccentric path, or a snail-cam shaped disk, which causes the spacing and/or alignment between a circumference of the disk and the transducer to vary, which variance may be detected by the transducer for providing an indication of the angular position of the rotor.

According to another aspect of the invention, there is provided a sensing arrangement which includes a sensor as hereinbefore described; and a movable member movable along a movement path in proximity to the transducer of the sensor. The movable member may include at least one index formation.

The index formation may be in the form of a tooth formation of a ferrous material. The transducers may then be arranged to interact with the index formation on the movable member, for example the transducers may be spaced such that formations on the movable member moving in the proximity of the transducers influence their characteristics.

For example, the movable member may include an index rotor and the sensor may include at least two transducers, arcuately located about the rotor axis by an angle that does not equal a multiple of half the index pitch, each transducer being disposed to generate a signal upon arcuate movement of an index formation in the proximity of the transducer.

The index formations may be equi-spaced along an arc subtended about the rotor axis by an arc angle, a whole number of index formations, being different from the number of transducers, being disposed along a circumferential arc on the rotor, subtended by the arc angle, so that the spacing between two adjacent transducers and between two adjacent index formations is a fraction of each other. In another embodiment, the sensor may have three transducers for detecting movement and direction of movement.

According to another aspect of the invention, there is provided a braking arrangement, which includes a sensing arrangement as hereinbefore described; and a brake which is selectively actuatable by the sensor when undesired movement of the movable member is detected by the detection circuit of the sensor for braking the movable member. The invention extends to a vehicle which includes a braking arrangement as hereinbefore described, operatively connected to a braking system of the vehicle, for selectively braking at least one wheel of the vehicle when undesired movement of the wheel of the vehicle is detected by the detection circuit. The invention further extends to a method of sensing movement of a movable member, the method including generating an oscillation signal in a loop circuit which includes at least one transducer positioned proximate a movement path of the member, the oscillation frequency of the loop circuit being defined by the characteristics of the transducer; and detecting a change in the oscillation frequency of the loop circuit in response to a change in the characteristics of the transducer caused by variations in the relative positioning of the movable member and the transducer. The invention will now be described, by way of example only, with reference to the following diagrammatic drawings, in which: Figure 1 shows a schematic block diagram of a braking arrangement, in accordance with the invention; Figure 2 shows a schematic block diagram of an embodiment of a sensing arrangement, in accordance with the invention; Figure 3 shows a schematic block diagram of a vehicle braking arrangement in accordance with the invention; Figure 4 shows an axial view of part of another embodiment of a movement sensor in accordance with the invention; Figure 5 shows an axial view of yet another embodiment of a sensor in accordance with the invention; and Figure 6 shows a sectional radial view of the sensor of Figure 4.

Referring to the drawings, reference numeral 10 generally refers to a braking arrangement in accordance with the invention. The braking arrangement includes a sensing arrangement 12 and a brake controller 14. The sensing arrangement 12 includes a sensor 16 (shown in broken lines) and a movable member 18 movable along a movement path, in this case a linear movement path, as indicated by arrow 20. It is to be appreciated that a similar sensing arrangement could be used where the movable member 18 is movable in an arcuate movement path, such as a vehicle wheel, where the sensing arrangement 12 may be used in a hill holding device. The movable member 18 has index formations in the form of ferrous metal teeth formations 22. The sensor 16 includes three transducers 24, 26 and 28, in the form of inductor coils which are connected to three loop circuits 30, 32 and 34, respectively. The loop circuits include signal generators in the form of oscillation circuits (not shown) of which the oscillation frequency is a function of the characteristics of the inductors 24, 26 and 28. In this instance, the inductance of each of the inductors 24, 26 and 28 will change depending on the relative position of each inductor and the teeth formations 22. The oscillation frequency of each loop circuit 30, 32 or 34 will then also change in response to the change in inductance of the associated inductor. The sensor 16 further includes a detection circuit 36 which includes three phase-locked loop circuits (PLL's) 38, 40 and 42, each of which is connected to the loop circuits 30, 32 and 34, respectively. A processor 44 is connected to the outputs of the phase-locked loop circuits 38, 40 and 42. A reference oscillator 52 provides a reference frequency to each of the PLL's 38, 40 and 42 for comparison with the oscillation frequency of each of the loop circuits 30, 32 and 34, respectively.

The braking arrangement 10 further includes a clutch engagement sensor 46 also connected to the processor 44 for sensing when a clutch engagement mechanism of a vehicle for example is engaged, and a gear selection sensor 48 for sensing a gear selection of the vehicle. In Figure 1 , the brake controller 14 is controllably connected to a braking assembly 50 of a wheel of a vehicle. The brake controller is connected to, and controlled by the controller 44.

In use, the loop circuits 30, 32 and 34 oscillate at a frequency of approximately 50MHz. When the position of a tooth 22 changes relative to the inductors 24, 26, or 28, its inductance changes which causes the oscillation frequency of the associated loop circuit 30, 32, or 34 to change. The change in frequency of the loop circuit 30, 32, or 34 is detected by the associated PLL 38, 40, or 42, by comparing the loop circuit's oscillating frequency with the frequency of the reference oscillator 52. A changing frequency thus provides an indication that a tooth 22 is moving in the proximity of the inductor 24, 26, or 28. The relative rate of change of the frequencies in the loop circuits 30, 32, 34 provides an indication of the direction of and speed of movement of the member 18 along the movement path 20.

As soon as the member 18 starts to move relative to the inductors 24, 26, and 28, the frequency in each loop circuit 30, 32 and 34 changes simultaneously. The direction of movement is determined by the increase or decrease in frequency in each of the loop circuits 30, 32 and 34. For example in Figure 1 , if the member 18 moves to the right, the frequency in the loop circuit 30 will increase, the frequency in loop circuit 32 will decrease and the frequency in loop circuit 34 will decrease. If the member 18 moves to the left, the frequency in loop circuit 30 will increase, the frequency in loop circuit 32 will increase and the frequency in loop circuit 34 will decrease- In response to the detection of movement, the gear selection of the vehicle, and the status of the clutch, the processor 44 then activates or deactivates the brake controller 14. For example, if a forward gear is selected and the clutch is engaged, the brake controller 14 would be activated when movement in a reverse direction is detected, thereby preventing the wheel of the vehicle from rolling back in a reverse direction. When the processor 44 subsequently senses the release of the clutch, the brake controller 14 is deactivated and the wheel 50 can move forward in a direction of movement corresponding with the gear selection of the vehicle.

Figure 2 shows another embodiment of the sensing arrangement

12. The same reference numerals have been used to refer to the same or similar components, shown in Figure 1.

In this embodiment, a movable member 19, in the form of a snail- cam shaped disk is rotatable about a rotation axis 21. Upon rotation of the member 19, the relative position between a circumference of the member 19 and the inductor 24, causes the oscillation frequency of the loop circuit 30 to change, which change is detected by the PLL 38. The controller 44 detects the direction and speed of rotation based on the frequency change detected by the PLL 38. It will be appreciated that the circumference of the member 19 could also move along a helical path, split washer fashion.

Figure 3 shows a vehicle braking arrangement 60 which includes a braking arrangement 10 in accordance with the invention, connected to a standard hydraulic braking system of a vehicle.

The braking arrangement 10 includes a sensor 16 and a brake controller 14. The sensor 16 co-operates with a toothed wheel 18 to sense rotational movement of an axle 68 of the vehicle. The processor 44 receives inputs from the sensor 16, a clutch engagement sensor 46 and a gear selection sensor 48 and activates, or deactivates a brake controller 14 in the form of a hydraulic valve which controls hydraulic fluid flowing under pressure from a hydraulic pump 68 towards a brake accessory 64 along a supply line 68.1 and a return line 68.2. The brake accessory 64 in this instance is retro-fitted to the brake master cylinder 62 and operates the brakes 70 of the vehicle when receiving pressurized hydraulic fluid.

Referring to Figure 4 of the drawings, another embodiment of the movement sensor 80 includes a ferrous metal rotor 82 having a rotor axis 84, and defining a plurality of equi-spaced indices in the form of teeth formations 86 on its circumference.

In this embodiment eight inductor transducers 88 protrude from a body 90, and are disposed equi-spaced along an arc subtended about the rotor axis 84 by an arc angle 92. Nine teeth formations 86.1 , 86.2 etc. are disposed along a circumferential arc on the rotor 82, the arc being subtended by the arc angle 92, so that the transducers 88 and the teeth formations 86 are spaced with the pitch between adjacent teeth formations 86 being eight ninths of the pitch between adjacent transducers 88.

In this specification, the term "index pitch" means the angle of arcuate spacing of adjacent indices on a rotor, about a rotor axis, or in the case of linear spacing the spacing of adjacent indices in a straight line.

In an alternative arrangement, to allow larger arcuate spacing of the transducers 88, each transducer 88 may be disposed at an angle, which is a multiple of the tooth pitch, from its position shown in Figure 4 of the drawings, i.e. spaced from the adjacent transducer 88, by a multiple of the tooth pitch plus one eighth of a tooth pitch.

For the purposes of this specification, the term "rotation" means any arcuate movement about an axis, irrespective of the angle of arcuate movement, including arcuate movement through small angles, rotation through 360°, etc. Clockwise rotation of the rotor 82 about the rotor axis 84 causes a tooth formation 86 to come into register with a transducer 88.1. Thereafter, after the rotor 82 has rotated by one eighth of the pitch between two teeth formations 86, a tooth formation 86.2 adjacent the tooth formation 86.1 in a clockwise position, comes into register with a clockwise adjacent transducer 88-2, and so forth, each rotation of the rotor 82 of one eighth of a tooth pitch in a clockwise direction causing a next transducer 88 and a next tooth formation 86 in a clockwise position, to come into register. Likewise, counter clockwise rotation of the rotor 82 results in consecutive teeth formations 86 and transducers 88 in a counter clockwise orientation, to come into register.

Arcuate displacement of a tooth formation 86 in the proximity of a transducer 88 causes an alteration of the electrical properties of each transducer 88, e.g. a change in the inductance of an inductor in the transducer 88. In response to the change in electrical properties, the transducer 88 transmits a signal, in the form of a pulse, e.g. a sine wave profiled pulse or a frequency shifted signal. The signals generated in the transducers 88 are transmitted to a processor (not shown) which includes logic circuitry, where the timing with which pulses are received from individual transducers 88 is used to determine the rotational speed and direction of rotation of the rotor 82, the frequency of signals being associated with the rotational speed, and the order in which pulses are generated in the different transducers being associated with the direction of rotation. The processor generates an output signal containing information regarding the rotational speed and direction of rotation of the rotor 82.

Referring to Figures 5 and 6 of the drawings, a further embodiment of a movement sensor 100 includes a rotor 102 in which a plurality of indices in the form of radial slots 104, are defined. Two proximity transducers 106 are disposed at an angle which does not equal a multiple of half the slot pitch, e.g.

4,25 slot pitches, about a rotor axis 108, so that each transducer 106 detects a slot 104 moving arcuately in the proximity of the transducer 106, as described above. Each transducer 106 generates a signal in the form of a pulse, which is transmitted to a processor. In another arrangement, each transducer 106 may direct an optical beam, such as a laser beam, or the like, in an axial direction towards a radial zone on the rotor 102 where the slots 104 are defined, to detect the presence or absence of a slot 104 in a path of the beam. Other embodiments may include transducers which are typically used in rotation sensors used in Antilock Braking Systems (ABS) in motor vehicles.

In use, rotation of the rotor 102 causes the slots 104 to move arcuately past the transducers 106. Pulse signals are generated in the transducers 106, the timing of which corresponds to the rotational speed of the rotor 102. The pulse signals are transmitted to a processor (not shown) in which an output signal is generated which includes information regarding the rotational speed of the rotor 102.

The accuracy of the sensors 80 and 100 in this embodiment can be improved by the addition of more transducers. Particularly, the embodiment of the rotation sensor 100 shown in Figures 5 and 6 may include three transducers 106, which will enable the rotation sensor 100 to determine the direction of rotation of the rotor 102 even when it is accelerating or decelerating. In the arrangement shown, including only two transducers, the direction of rotation of the rotor can only be determined from the timing of the pulse signals if the indices are not spaced in multiples of the index pitch and if the rotational speed of the rotor 102 is reasonably stable. The invention as illustrated holds the advantage of providing a relatively simple and low cost sensor, which can sense the speed and direction of movement of a movable member with a high degree of accuracy even with very little movement of the movable member. In particular, the embodiments illustrated in Figures 1 and 2 provide a sensing arrangement, in which the sensing accuracy is not primarily dependent on the number of transducers, but rather on the frequency detection accuracy of the detection circuit.

The invention, as illustrated has particular application in so-called hill holding devices in motor vehicles, where small rotational movement of a vehicle's wheels corresponds with movement of the vehicle on an incline.

Because of the accuracy and relative low cost, the illustrated invention has particular application in a wide range of braking systems, such as escalators, lifts, vehicle braking systems, conveyor systems and the like.

Claims

CLAIMS:

1. A sensor for sensing movement of a movable member along a movement path, the sensor including at least one transducer located in proximity to a possible movement path of the member, the transducer being connected in a loop circuit; a signal generator connected to the loop circuit, the signal generator being operable to generate a signal in the loop circuit at a frequency which is associated with the characteristics of the transducer, the frequency of the loop circuit being variable as a result of a change in the characteristics of the transducer caused by variation in the relative positioning of the member and the transducer; and a detection circuit for detecting variation in the frequency of the loop circuit.

2. A sensor as claimed in claim 1 , in which the transducer includes an inductive element having the characteristic that its inductance changes depending on the relative positioning of the movable member and the transducer.

3. A sensor as claimed in claim 1 or claim 2 in which the detection circuit includes a phase-locked loop associated with the loop circuit, the phase- locked loop being operable to detect a change in the oscillation frequency of the loop circuit.

4. A sensor as claimed in claim 3 which includes a processor, operable to receive a signal from the phase-locked loop when the frequency of the loop circuit changes and, in response, to calculate any one of the speed- and direction of movement of the member, based on the order and interval of the received signals.

5. A sensing arrangement which includes a sensor as claimed in any one of claims 1 to 4; and a movable member movable along a movement path running in proximity of the transducer of the sensor.

6. A sensing arrangement as claimed in claim 5, in which the movable member includes at least one index formation positioned to interact with the transducers of the sensor.

7. A sensing arrangement as claimed in claim 6, in which the index formation is in the form of a tooth formation of a ferrous material.

8. A sensing arrangement as claimed in claim 6 or claim 7, in which the movable member includes an index rotor and in which the sensor includes at least two transducers, arcuately spaced about an axis of the rotor by an angle that does not equal a multiple of half the index pitch, each transducer being disposed to generate a signal upon arcuate movement of an index formation in the proximity of the transducer.

9. A sensing arrangement as claimed in claim 8, which includes a plurality of index formations, the index formations being equi-spaced along an arc subtended about the rotor axis by an arc angle, a whole number of index formations, being different from the number of transducers, being disposed along a circumferential arc on the rotor, subtended by the arc angle, so that the spacing between two adjacent transducers and between two adjacent index formations is a fraction of each other.

10. A sensing arrangement as claimed in claim 5, in which the movable member is in the form of a snail cam.

11. A braking arrangement, which includes a sensing arrangement as claimed in any one of claims 5 to 10; and a brake which is selectively actuatable by a sensor of the sensing arrangement when undesired movement of the movable member is detected by the detection circuit of the sensor for braking the movable member.

12. A vehicle which includes a braking arrangement as claimed in claim

11 operatively connectable to a braking system of the vehicle, for selectively braking at least one wheel of the vehicle when undesired movement of the wheel or the vehicle is detected by the detection circuit.

13. A method of sensing movement of a movable member, the method including generating an oscillation signal in a loop circuit which includes at least one transducer positioned proximate a movement path of the member, the oscillation frequency of the loop circuit being defined by the characteristics of the transducer; and detecting a change in the oscillation frequency of the loop circuit in response to a change in the characteristics of the transducer caused by variations in the relative positioning of the movable member and the transducer.