GB2170009A

GB2170009A - Speed and direction sensing apparatus

Info

Publication number: GB2170009A
Application number: GB08600167A
Authority: GB
Inventors: Robert Paul Page; Stuart Ian Howarth
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1985-01-22
Filing date: 1986-01-06
Publication date: 1986-07-23
Also published as: GB8600167D0; GB8501517D0; DE3601197A1; FR2576419A1; JPS61170658A

Abstract

A speed and direction sensing apparatus for a rotary shaft includes a disc for mounting on the shaft, the disc has first and second series of teeth 11, 12 formed on its periphery and an eddy current type sensor 13 responsive to the passage of the teeth. The teeth 11 of the first series are wider than the teeth 12 of the second series and the teeth 12 of the second series are spaced from one tooth of the first series by a space equal to the width of the teeth of the second series and from the next adjacent tooth by a space equal to the width of a tooth of the first series. The signals from the sensor are passed to a flip flop and the output of the flip flop is a waveform having a 1/1 mark space ratio when the shaft is rotated in one direction and waveform having mark space ratios of 1/2 and 2/1 when the shaft rotates in the opposite direction. <IMAGE>

Description

SPECIFICATION Speed and direction sensing apparatus This invention relates to an apparatus for providing an indication of the speed and direction of rotation of a rotary shaft.

It is well known in the art to utilize a disc or wheel driven by the shaft and to provide irregularly spaced teeth on the disc or wheel the passage of which is sensed by a sensor. From the signal provided by the sensor it is possible to determine the direction of rotation of the shaft. An example of such an apparatus is to be found in British Patent Specification 1591376. It is also well known in the art to provide a series of regularly spaced teeth on the disc or wheel and to use a sensor to sense the passage of the teeth, the output signal of the sensor providing an indication of the speed of the shaft.

United States specification 4370614 discloses a system in which the speed and direction of rotation of a shaft can be determined by providing a series of regularly spaced teeth on a disc or wheel driven by the shaft and by using a pair of sensors which sense the passage of the teeth, the sensors being spaced by a distance which is effectively equal to one quarter of the pitch of the teeth. The signals provided by the sensors are then processed to provide an indication of the direction of rotation of the shaft and the signal provided by one of the sensors can be utilized to provide an indication of the speed of rotation of the shaft. This system however requires the provision of two sensors which require careful adjustment relative to each other and to the disc.

The object of the present invention is to provide an apparatus for providing an indication of the speed and direction of rotation of a rotary shaft in a simple form.

According to the invention an apparatus for the purpose specified comprises a disc adapted to be coupled to the shaft so as to rotate therewith, first and second series of marking elements on said disc, the elements of each series being equiangularly spaced and alternately arranged with the elements of the other series about the axis of rotation of the disc, the elements of one series being unequally spaced relative to the adjacent elements of the other series, a sensing device for providing electrical signals indicative of the passage of the elements past the device and means for processing said signals to provide an indication of the speed and direction of rotation of the disc.

In the accompanying drawings: Figure 1 is a developed view to an enlarged scale of a toothed disc and a sensing device, Figures 2 and 3 are curves indicating the output of the sensing device when the disc is rotated in opposite directions from the position shown in Figure 1, Figures 4, 5 and 6 show three types of pulse signal which can appear at the output of a processing stage for the output of the sensing device, and Figure 7 is a circuit diagram for processing the signals shown in Figures 4, 5 and 6.

An application for the apparatus exists in a vehicle transmission system in which it is required to know for the purpose of control of the transmission, the direction of rotation of the output shaft of the gearbox forming part of the transmission and also the forward speed of the vehicle.

The main element of the sensing device comprises a disc which is coupled to the output shaft of the gearbox and Figure 1 illustrates a developed view of the periphery of the disc. The disc is provided with two series of teeth. The teeth of the first series are referenced 11 and are equiangularly spaced about the periphery of the disc. The teeth of the second series are referenced 12 and are again equiangularly spaced about the periphery of the disc. The teeth of the two series are alternately arranged but the spacing between one tooth of one series and the adjacent teeth of the other series is unequal. In addition, the teeth of the first series are wider than the teeth of the second series and it is arranged that the widths of the smaller and larger spaces is equal to the widths of the smaller and larger teeth.

Associated with the disc is an eddy current type sensing device 13 which provides an electrical signal when the edges of the teeth pass the device. In Figure 1 the sensing device is shown to be located opposite a space defined between a pair of teeth. In addition, marked on Figure 1 are arrows indicating the direction of rotation of the disc relative to the sensing device, the arrow F indicating forward rotation of the disc and the arrow R reverse rotation.

If the disc is moved in the forward direction from the position shown in Figure 1, the forward edge of one of the teeth 11 will first pass the sensing device followed by the trailing edge of the tooth and then the leading edge of the following tooth 12. The output signal from the device 13 will therefore be as shown in Figure 2. If on the other hand the disc is rotated in the reverse direction then the first edge to pass the sensing device 12 will be the leading edge of a tooth 12 followed by the trailing edge of the same tooth and then the leading edge of the following tooth 11. The output will therefore be as shown in Figure 3. From Figure 2 it will be seen that the rising edges of the pulse signal are equispaced the reason for this being that the gaps between the teeth reflect the width of the teeth.From Figure 3 it will be seen that the interval between the rising edges of the pulses is unequal. This fact can be used to determine the direction of rotation of the disc.

In order to process the signals obtained from the sensing device 13, the signals are first passed to a flip flop circuit to be described, which changes its state at the receipt of a rising signal from the sensing device. The output of the flip flop therefore when the disc is rotating in the forward direction will be as shown in Figure 4 and the mark space ratio will be unity. When the disc is rotating in the reverse direction two types of signal as shown in Figures 5 and 6 can be obtained depending upon which rising edge is first received by the flip flop.The mark space ratio of the signal shown in Figure 5 is 1/2 and the mark space ratio of the signal shown in Figure 6 is 2/1. In order to provide a reliable indication of the direction of rotation it is therefore necessary to supply the signals from the flip flop to a circuit which can distinguish between the signals and provide an appropriate output signal or signals. The circuit is shown in Figure 7, the circuit also illustrating the flip flop which receives the signals provided by the sensing device.

Referring to Figure 7 the circuit includes positive and negative supply lines 14, 15 for connection to a source of d.c. supply, the supply voltage in the particular example, being 12 volts. The circuit input 16 is connected to the sensing device and a resistor R1 is connected between the supply line 14 and the circuit input. The circuit input is also connected to the clock terminal of a "D" type flip flop IC1 which has its D input connected to its inverted Q output terminal. The supply terminal of the flip flop is connected to the supply line 14.

The non-inverted output terminal Q of the flip flop is connected by way of a resistor R4 to a comparator IC2 the purpose of which is to ensure that an output pulse of 12 volts will be obtained. The output of the comparator IC2 is connected to the supply line 14 by way of a resistor R5 and to one end of a resistor R6 the opposite end of which is connected to one plate of a capacitor C1, the other plate of which is connected to supply line 15. The capacitor C1 has an appreciable capacitance value and the capacitor becomes charged to a level depending upon which of the wave forms shown in Figures 4, 5 and 6 appears at the output of the comparator IC2. The wave form shown in Figure 4 since it has an equal mark space ratio will cause the voltage across the capacitor C1to assume approximately 6 volts.The wave form shown in Figure 5 will cause the voltage across the capacitor to assume approximately 3 volts and the wave form shown in Figure 6 will cause the voltage across the capacitor to assume approximately 9 volts. The remaining portion of the circuit shown in Figure 7 is for distinguishing the various voltages and also for providing an indication of when the disc is at rest.

The voltage appearing across the capacitor is applied to two comparators IC3 and IC4 the common collector outputs of which are connected together. Each comparator is provided with a reference voltage source comprising adjustable potentiometer chains respectively and the reference source to comparator IC4 is adjusted so that the output of comparator IC4 will be low when the d.c. voltage across capacitor C1 is greater than about 8 volts. The reference voltage of comparator IC3 is adjusted so that its output will be low when the voltage across the capacitor C1 is less than about 4 volts. Thus unless the voltage across the capacitor is between 4 and 8 volts the combined output of the two comparators will be low.

When the output is high a transistor TR1 is turned on causing the illumination of a light emitting diode D1 indicating that the disc is rotating in the forward direction. When the combined output of the comparators IC3, IC4 is low this means that the disc is rotating in the reverse direction but it may also indicate that the disc is at rest. It is therefore necessary to determine whether the disc is at rest and this is achieved by the remaining portion of the circuit shown in Figure 7.

The input terminal 16 is connected by way of a capacitor C2 which in conjunction with a resistor R7, constitutes a differentiating circuit. The junction of the capacitor and resistor are connected to the base of a transistor TR2 and a diode D2 is connected between the base and the supply line 15. The transistor will therefore only be switched on when positive spikes are present on its base. The emitter of the transistor is connected to supply line 15 and the collector is connected to the supply line 14 by way of a pair of resistors R8, R9 connected in series with the junction of the resistors being connected to one plate of a capacitor C3 the other plate of which is connected to the supply line 15. When transistor TR2 is in a nonconducting state capacitor C3 will be fully charged by way of resistor R9 but when transistor TR2 conducts the capacitor will be partially discharged.The voltage across the capacitor C3 is sensed by a further comparator IC5 which has a reference voltage applied to it by means of a suitable potentiometer network. The potentiometer network is adjusted so that the output of the comparator is low when the capacitor C3 is fully charged i.e. when the disc is not rotating. In practice the disc must rotate at a so-called transition speed at which the voltage across the capacitor C3 is reduced sufficiently, before the comparator output becomes high. The comparator IC5 is provided with feedback which provides hysteresis.

The output of the comparator IC5 is connected by way of a resistor to the supply line 14 and to the inputs of a NAND gate IC6 the output of which is used to control the conduction of a transistor TR3 which when conducting causes illumination of a light-emitting diode D3 indicating that the disc is at rest.

To obtain a signal of reverse rotation the combined output of the comparators IC3 and IC4 is connected to the input terminals of a NAND gate IC7 the output of which is connected to one input of a further NAND gate IC8. The other input of this gate is connected to the output of the comparator IC5 and the output of the NAND gate IC8 will therefore be low when the disc is rotating in the reverse direction. The output of the NAND gate IC8 is connected to the input terminals of a further NAND gate IC9 the latter being used to control the conduction of a transistor TR4 which when conducting causes illumination of a light emitting diode D4, the diode being illuminated when the disc is rotating in the reverse direction.

The circuit provides visual indication of when the disc is rotating in the forward direction by illumination of diode D1, when the disc is at rest by illumination of the diode D3 and when the disc is rotating in the reverse direction by illumination of the diode D4. Whilst the diodes may be provided for visual in spection, the transmission control system would be provided with appropriate signals.

The output of the comparator IC2 is a waveform of one of the three types seen in Figures 4, 5 and 6.

The intervals between the positive going edges of each of the waveforms are the same, as also is the case with the negative going edges, and depend only upon the speed of rotation of the disc. All that is required therefore is to measure the time interval between two adjacent positive going edges and this can be achieved by using the positive going edges to clear and start a counter 17 which counts the pulses produced by a suitable clock 18, the count value being loaded into a suitable latch 19 before the count value is cleared. The value of the count loaded into the latch will correspond to the average speed of the disc between two positive going edges.

Instead of using the circuit shown in Figure 7 the output pulse train from the sensor can be fed to an input of a microprocessor which input is capable of detecting both positive and negative going edges.

When the disc is rotating in the forward direction the positive going edges of the pulses as seen in Figure 2 are equally spaced and using the clock of the microprocessor it is possible to provide a speed signal If the disc is rotating in the reverse direction the positive going edges are unequally spaced. However, if the reverse rotation of the disc is sensed the microprocessor can be made to respond to the negative going edges of the pulses which are equally spaced.

Within the memory of the microprocessor is a bit which is called NEGATIVE FLAG and if this bit is set to "1" the processor responds to the negative going edges and when it is cleared to '0' it responds to the positive going edges.

Let it be assumed that from rest the shaft starts to rotate in the reverse direction so that the pulse train seen in Figure 3 is supplied to the input of the processor. The "Negative Flag" will not be set and so the processor responds to the positive going edges 0, 2, 4, 6 etc. Using the clock it records the times at which the aforesaid edges occur and calculates three periods as follows: Time for edge 2 - Time for edge 0 = Old Period (OP) Time for edge 4 - Time for edge 2 = Period (P) Time for edge 6 - Time for edge 4 = New Period (NP) It then checks if OP + NP P 2 = In the case of reverse rotation this is not true but if the disc had been rotating in the forward direction it would have been true as can be determined from Figure 2.The processor in this case assumes that the disc is rotating in the reverse direction and the "NEGATIVE FLAG" is set to "1". However, the periods which are now stored relate to the wrong direction of rotation and hence a "WAIT FLAG" in the memory is set and the values of Period and Old Period are set to an arbitorily chosen maximum value which corresponds to the lowest speed at which disc rotation can be detected. As soon as all three periods have been updated with actual values the "WAIT FLAG" is removed and speed calculation is carried out.

This process is repeated every time there is a change in the direction of the disc.

In order to calculate the speed the value of 1/Period is used for forward rotation and -1/Period for reverse rotation.

If the disc is rotating at a constant speed then OP = NP and a check for the direction of rotation could be effected comparing NP with P. During periods of acceleration and deceleration it is assumed that the acceleration or deceleration is constant over the three periods. In practice exact equality between periods is unlikely and since it is difficult to describe the function "approximately equal to" in software, in practice the 'Period' is checked for lying between

Claims

1. An apparatus for providing an indication of the speed and direction of rotation of a rotary shaft comprising a disc adapted to be coupled to the shaft so as to rotate therewith, first and second series of marking elements on said disc, the elements of each series being equiangularly spaced and alternately arranged with the elements of the other series about the axis of rotation of the disc, the elements of one series being unequally spaced relative to the adjacent elements of the other series, a sensing device for providing electrical signals indicative of the passage of the elements past the device and means for processing said signals to provide an indication of the speed and direction of rotation of the disc.

2. An apparatus according to Claim 1 in which said marking elements are in the form of teeth and said sensing means produces rising and falling signals as the edges of a tooth pass the sensing device.

3. An apparatus according to Claim 2 in which the teeth of the first series are wider than the teeth of the second series, the wider spaces between the teeth have the same width as the teeth of the first series and the narrower spaces between the teeth have the same width as the teeth of the second series;

4. An apparatus according to Claim 3 including a flip flop connected to receive the signal produced by the sensing device, and responsive only to alternate changes of signal, the output of said flip flop being one of three alternative pulse signals, the first being a pulse signal having a 1/1 mark space ration being obtained when the shaft is rotated in one direction and the second and third pulce signals being alternative signals which can be obtained when the shaft is rotated in the opposite direction, the mark space ratios being 2/1 and 1/2 respectively.

5. An apparatus according to Claim 4 including a first capacitor which is charged to a value determined by the mark-space ratio.

6. An apparatus according to Claim 5 including first and second comparators responsive to the voltage across said capacitor, said comparators having their outputs connected together and to a first indicator means, the reference voltages applied to said comparators being such that said indicator means is rendered operative when the mark-space ratio is substantially 1/1.

7. An apparatus according to Claim 6 including a second capacitor, means for charging said second capacitor, a transistor which when conductive acts to discharge said second capacitor, circuit means responsive to the output of said sensing means and acting to turn said transistor on at said alternate changes of signal, a third comparator responsive to the voltage across said second capacitor, reference voltage means for supplying a reference voltage to said second comparator whereby the output of said second comparator will be low when the shaft is at rest, and second indicator means responsive to the output of the second comparator and which is rendered operative when said shaft is at rest.

8. An apparatus according to Claim 7 including third indicator means responsive to the output of said first and second comparators and said third comparator and which is rendered operative when said shaft is rotating in the other direction.

9. An apparatus according to Claim 4 including a counter responsive to said alternate changes of signal at the output of said flip flop, a clock for providing pulse signals to said counter and a latch into which the count value of said counter is loaded before the counter is cleared, said count value being indicative of the speed of rotation of the shaft.

10. An apparatus according to Claim 3 including microprocessor means operative to initially check the times between alternate changes of signal from the sensing means to determine whether the most recent period between the alternate changes of signal is substantially equal to the average of the previous two periods and if it is to compute the speed of the shaft from the value of the period and if it is not to determine the period between the other changes of signal and compute the speed therefrom.

11. An apparatus for providing an indication of the speed and direction of a rotary shaft substantially as hereinbefore described with reference to the accompanying drawings.