GB2207506A - Apparatus for measuring shaft torsion - Google Patents

Abstract

A sensor arrangement 11, 12, 14 responsive to relative angular positions of two locations on a shaft 10 to provide, on a line 17, filtered pulses whose frequency are proportional to speed and torsion respectively of the shaft 10. A counter 21 is responsive to the pulses on line 17 and to a reference frequency from a clock 20 to provide a count value corresponding to the product of torsion and time. A counter 22 is responsive to the reference frequency to provide a time count value. Cyclically recurring pulses on line 17 e.g. once per shaft revolution as determined by a counter 18 and output over a line 31 cause registers 24, 25 to store the most recent cumulative values from the counter 21, 22 respectively. When it calculates shaft torsion, a control means 27 reads the register values and resets registers and counters. In a similar arrangement, the counter 18 and its associated register 23 are responsive to the pulses on line 17 to provide values corresponding to speed of the shaft 10. <IMAGE>

Description

"APPARATUS FOR MEASURING SHAFT TORSION" It is known, for example, from GB-A-2133885A to measure torsion on a shaft by means of pulses from a sensor arrangement which is responsive to angular positions of two axially spaced locations on the shaft. The sensor arrangement generates pulse trains whose frequency is proportional to the shaft speed and which has a pulse width corresponding to the shaft torsion. The pulse widths are, for a given shaft cross-section, proportional to the torque thereon. The duration of the pulses is determined by the magnitude of a high frequency count over a predetermined number of the pulses.

Where a count corresponding to the pulse duration is to be read into a computer for subsequent use, that count is previously read into a buffer register which is then accessed by the computer. If the count is read into the buffer register at predetermined intervals, to await subsequent accessing by the computer, the value in the buffer may be out of date when accessed by the computer. The present invention provides an apparatus by means of which a count value in a buffer register continues to be updated to a time substantially immediately before being accessed for subsequent use or display.

According to the invention an apparatus for measuring torsion of a shaft comprises means for generating a train of pulses having a first frequency corresponding to the shaft speed and a pulse duration corresponding to the shaft torsion, means for generating a second, reference frequency, means for counting the number of pulses on one of said frequencies occurring during a predetermined number of pulses of the other of said frequencies, a latchable register for storing the value in said counting means, said register being responsive to cyclically occurring pulses of said one frequency to update the value stored therein, and means for periodically reading the value in said register, whereby the value read from said register on each occasion is a recently updated value.

In a particular embodiment said means for reading the value in said register comprises means for generating signals which successively: stop transfer to said register of a value from said counting means; clear the value in said counting means after the value in said register has been read and clear the value in said register.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a block diagram of an apparatus for measuring shaft torsion, Figure 2 is a pulse chart showing an operation of the arrangement of Figure 1, Figure 3 is a diagram on a filter circuit forming part of the arrangement of Figure 1, and Figure 4 is a pulse chart showing operation of the circuit of Figure 3.

As shown in Figure 1 a shaft 10 carries discs 11, 12 which are drivingly connected to axially spaced positions on the shaft 10. The discs 11, 12 are identical are of magnetic material and are each provided with sixteen equi-angularly spaced teeth. A variable reluctance sensor 14 is positioned to one side of the discs 11, 12 and as the shaft 10 rotates the senor 14 provides, on a line 15, a train of pulses whose frequency is proportional to the speed of the shaft 10 and whose pulse duration corresponds to the duration of each alignment of apertures in the discs 11, 12. The pulses on the line 15 are applied to a filter circuit 16, later to be described and shown in detail in Figure 3. Filtered pulses from the circuit 16 are applied on a line 17 to the clock input CK of a dual four-bit counter 18 of a type commercially available under the designation 74 HC 393.

The signal on line 17 is also applied to one input of an AND gate 19 whose other input is a pulse train from a 6MHZ clock 20. The output of the gate 19 is connected to the clock terminal of a counter 21 which is identical with the counter 18. The 6MHZ pulses are also applied to the clock terminal of a third counter 22 identical with the counters 18 and 21.

Three eight-bit registers 23, 24, 25 of the type commercially available under the designation 374 have their enable terminals connected through a line 26 to a LATCH output of a programmable logic circuit 27 of the type commercially available under the designation PAL16R4. Clock pulses for the circuit 27 are provided by the 6MHZ clock 20.

The positive-going edge of a signal at the QD output of the counter 18 is applied on a line 30 to the circuit 27 to initiate the LATCH signal on line 26. The positive-going edge on line 30 occurs only every sixteenth of the pulses on line 17, that is once every revolution of the shaft. The effect is that assuming a constant torsion of the shaft 11 during a sampling interval, asymmetry of the discs 11, 12 or tolerance errors between them are cancelled out.

The cumulative values in the registers 23, 24, 25 are transferred to an input data bus 28 of a computer 29.

At varying intervals determined by its programmed operation the computer 29 sequentially reads out the contents of the registers 23, 24, 25. In such a reading operation the computer 29 first generates a signal pulse on a line 40 to the output control connection OC of the register 23. The pulse on line 40 is also applied to the circuit 27 which responds by inhibiting the LATCH signal on line 26 thereby preventing further transfer of count values to the registers 23, 24, 25. After an interval sufficient for the contents of register 23 to have been transferred on the bus 28 to the computer 29 the latter generates a second signal pulse on a line 41 to the output control OC of the register 24 to cause the contents of the latter to pass via the bus 28 to the computer 29.Finally the computer 29 generates a signal pulse on a line 42 to the output control OC of the register 25 and to the circuit 27. The circuit 27 responds to the end of the pulse on line 42 by generating a CLEAR signal on the line 30 thereby clearing the values in the counters 18, 21, 22.

Pulses on line 17 are applied to the circuit 27 by of a line 43, and the first of these pulses following the pulse on line 42 ends the CLEAR signal on line 30 and initiates a LATCH pulse on line 26. Since each of the counters 18, 21, 22 has been reset, the values in the counter 23, 24, 25 are all reset to zero. At the end of the CLEAR signal on line 30 the counters 18, 21, 25 recommence operation.

The above sequence is indicated in Figure 2, the figures in brackets being those of the corresponding features of Figure 1 in which the indicated conditions are present.

It will be seen that the value in the register 23 corresponds to the total angular rotation of the shaft between times of access by the computer 29. The value in register 24 is a product of the shaft torsion and the time between successive access by the computer 29 and the value in register 25 is proportional to the time between successive occasions of computer access.

The computer 29 may therefore determine both shaft speed and torsion from the values in the registers 23, 24, 25 and may calculate the torque on the shaft 10 from the torsion value and the dimensions of the shaft.

As shown in Figure 3 the filter circuit 16 includes an exclusive OR gate 50 and an AND gate 51 each of which has one input connected to the line 15. The other input of the gate 50 is connected to the line 17. The output of the gate 50 is connected to the clear terminal CL of a four-bit counter 52 whose QD output is connected to the second input of the gate 51 and to an inverting input of an AND gate 53. The other input of the gate 53 is connected to the line 17. The outputs of the gates 51, 53 are connected to inputs of an OR gate whose output is connected to the input of a D-type flip-flop 55. A 1.5MHZ generator 56 is connected to the clock terminal CK of the flip-flop 55, whose Q output is connected to the line 17. The generator 56 is connected to one inverting input of a NAND gate 57, the other inverting input of that gate being connected to the QD output of the counter 52. The output from the gate 57 is connected to the clock terminal of the counter 52.

Figure 4 shows the signals on lines 15 and 17 and at locations indicated in Figure 3. Since the circuit 16 as a whole effects, in a manner to be described, a delay between the input signal on line 15 and the output signal on line 17, the signal at X exists when one only of the input or output signals is present.

In the absence of a signal on line 17 a pulse on the line 15 will thus result in a high level signal at X.

The counter 52 thereby starts and produces a signal at Y after a delay T corresponding to a predetermined number of pulses from the generator 56. The signal at Y is applied through the gate 57 to stop further incrementing of the value in the counter 52. The signal at Y combines with that on the line 15 to give a high level signal at P. The resulting high level signal at R sets the Q output of the flip-flop 55 high.

The signal on line 17 thus starts at a time T after that on the line 15. The signal on line 17 causes the signal at X to go low, clearing the counter 52 until the end of the pulse on line 15. During a pulse on line 15 the signal at S occurs only in the absence of a signal at P and in the presence of a signal on line 17.

The signal at R and consequently the signal on line 17 is thus equal in duration to the sum of the durations of the signals at P and S.

In the event of a noise signal occurring during one of the pulses on line 15, as shown at N1 in Figure 4, or during an interval between those pulses, as shown at N2, the signal at X will go high and the counter 52 will start. Providing the duration of either noise signal is less than the time T the signal at X will become low before the signal at Y is generated.

Claims (6)

1. An apparatus for measuring torsion of a shaft, comprising means for generating a train of pulses having a first frequency corresponding to the shaft speed and a pulse duration corresponding to the shaft torsion, means for generating a second, reference frequency, a first counter for counting the number of pulses of one of said frequencies occur ring during a predetermined number of pulses of the other of said frequencies, a first latchable register for storing the value in said first counter, said register being responsive to cyclically occurring pulses of said other frequency to update the value stored therein, and control means for periodically reading the value in said register, whereby the value read from said register on each occasion is' a recently updated value.

2. An apparatus as claimed in Claim 1 in which said means for reading the value in said register comprises means for generating signals which successively: stop transfer to said register of a value to said counting means; clear the value in said counting means after the value in said register has been read, and clear the value in said register.

3. An apparatus as claimed in Claim 1 or Claim 2 in which said one frequency is said second, reference frequency and said other frequency is said first frequency.

4. An apparatus as claimed in any preceding claim which includes a second counter responsive to said reference frequency, and a second latchable register responsive to said cyclically occurring pulses to store updated values from said second counter, said control means periodically reading the values in said first and second registers.

5. An apparatus as claimed in Claim 5 in which said control means includes means for calculating a torsion value from the values in said first and second registers.

6. An apparatus for measuring torsion on a shaft, substantially as hereinbefore described with reference to the accompanying drawings.