GB2068127A - Measuring movement - Google Patents

Abstract

Apparatus for measuring movement e.g. of scratching of patients suffering from itching diseases generates a movement-detection signal and measures a cumulative total of time intervals during which the magnitude of the movement-detection signal exceeds a predetermined threshold value. An electromagnetic stepper motor (11) has an arm (14) extending from its rotor (13), such that scratching motion rotates the rotor. Electrical signals are generated in the coils (12) of the stepper motor (11) and compared with a reference voltage by a monostable circuit (17). During intervals when the signals are greater than the reference voltage, an actuator (19) holds a sprung restraining arm off the balance wheel of a watch so that the watch records the cumulative total of scratching time. In other arrangements the criterion for recorded motion may be frequency and other movements e.g. vehicle cab vibrations may be measured. <IMAGE>

Description

SPECIFICATION Apparatus and method for measuring movement The present invention relates to an apparatus for and method of measuring movement, and is concerned in particular but not exclusively with the measurement of patient movement caused by scratching.

Many diseases are accompanied by a sensation in the patient of itching, and it is a requirement in assessing the nature of the disease, and the effectiveness of its treatment, to be able to measure the extent of itch which is caused. The investigation of itch has been hindered by the lack of an objective measurement of this sensation, as assessment has generally relied upon a patient's subjective impression of the sympton. An alternative approach has been to measure scratch which is the usual consequence of itch. Scratch has been assessed during sleep in itchy skin diseases using closed circuittelevision, action potentials from forearm electrodes, and vibration transducers attached to the bed.

A simpler method of measurement of itch has been proposed by R. Felix and Sam Shuster and has been described in a paper by these authors entitled "A new method for the measurement of itch and the response to treatment" published in the British Journal of Dermatology (1975) 93,303. This method was to take an automatic watch with date facility and to remove the escapement consisting of the balance and pallets. This modification meant that if the rotor was moved in either direction, the hands of the watch would rotate rapidly to dissipate the energy created in the main spring bythe movementofthe rotor. In such an arrangementthe rate at which the hands of the watch are carried around is very high and a 24 hour count on the dial may be completed in a few minutes.Because of this, the date indicator was used to tell how many times the 24 hour count has been completed. The method of calibration used was to attach the modified watch to a rotating turn table which rotated at a fixed rate of rotation, and to plot a graph showing number of rotations of the turntable against number of meter units recorded on the date indicator. Thereafter a translation of date meter units into movements was obatined by noting the number of meter units against the graph and deriving from the graph a supposed number of equivalent movements. It has been found that the use of modified self-winding watches to measure scratching movements as set out above has several limitations in practice.These include inadequate sensitivityto respond to all scratch movement (the detector is very insensitive due mainly to its mass and relatively large bearing surface), and, because of the mass of the pendulum, a marked position sensitivity so that the detector does not respond to movement in all planes (dead points occur where the detector fials to respond to certain angles of movement).

Furthermore, the response of the previous system was related to the velocity of the scratch movement so that the response to vigorous scratching was greaterthan the response to mild scratching. In consequence, calibrating these previous meters on a rotating table at constant velocity was an invalid method of calibration. Other points are that the output from the modified watches was in arbitrary units, thereby making comparisons between groups difficult, and also overall sensitivity varied according to the grade of watch movement.

Considering furtherthe problem of calibration in the previous method, the principle of detection of movement was the measurement of the kinetic energy acquired by the rotor of the modified watch during the scratch movement. This energy could either be transferred direct to the geartrain of the watch (slow movement) or stored in the spring (fast movement) and then released to the gear train. In addition to the difficulty of dead points mentioned above, inaccuracies may arise due to over-run by the geartrain arising from inertia ofthe system. This is an important error becuse of its cumulative nature.

The number of turns of the hands recorded may vary considerably according to the type of movement of the watch. For example a movement in one direction may not complete a turn of the rotor, but the following reverse movement may complete the turn.

Alternatively a single movement in one direction may through inertia produce a complete turn of the rotor. The problem of over-run arises essentially because there is no reservoir of energy stored in the main spring.

In contrast to the irregular nature of the scratching movements being measured, the movements used for calibration were regular. On the calibration curve the number of rotations of the turn-table were represented byx and the number of meter units by y.

Whilst a curve could of course be plotted of number of rotations on the turn-table against meter units, this was only valid for the particular set of conditions on the tu rn-table. For example if a patient were to scratch slowly for 1 minute this might record x' meter units. The same patient scratching quickly for 1 minute might record a number of meter units greaterthan x', and the same patient scratching very quickly might in some circumstances record less than x' meter units. Thus no reliable relationship exists between the number of units of movement calculated by comparing the meter units with the calibration curve, and the actual scratching movements which gave rise to the count on the meter.

It is one object of the present invention, in connection with its aspect relating to measurement of scratching movements by patients, to provide a simple and robust movement meter capable of providing a measurement which can be reliably related to the amount of scratching movement which has occurred. However it will be appreciated that in its broader aspect, the invention is applicable to fields other than detection of scratching movements.

According to the present invention there is provided apparatus for measuring movement comprising detection means for detecting movement having a characteristic beyond a predetermined threshold value or in a predetermined range ofvalues, and output means for measuring a cumulative total of time elapsed during time intervals when movement is detected by the detection means beyond the said value or in the said range.

According to the present invention in a second aspect there is provided apparatus for measuring movement comprising a rotor rotatably mounted on a base, the rotor having its centre of gravity spaced from its axis of rotation for producing rotary movement of the rotor during translational movement of the base, detection means for deriving an electrical movement-detection signal produced by disturbance of a magnetic field by rotation of the rotor, and output means for producing in response to the electrical movement-detection signal an output signal representative of a parameterofthe movement of the base.

The invention has particular application where the said parameter of the base movement is a cumulative total oftime elapsed during time intervals when movement of the base is detected, by the detection means, having a characteristic (for example in repetitive movement an amplitude and/or frequency) beyond a predetermined threshold value or in a predetermined range of values. The invention is further particularly applicable where the said time intervals are intervals when the magnitude ofthe electrical movement-detection signal is greaterthan a predetermined threshold, although by way of example the apparatus may be made to respond in other examples in relation to movement giving rise to a movement-detection signal having a frequency above or below a frequency threshold or in a frequency range.

The invention has particular application in the field of measurement of patient movement caused by scratching. In such an application the said base may comprise a housing for the rotor provided with a strap for fastening the base to an arm or leg of the patient.

There is also provided in accordance with the invention, a method of measuring movement of a subject (usually human) under examination comprising the steps of detecting subject movement having a characteristic beyond a predetermined threshold value or within a predetermined range of values, and measuring a cumulative total of time elapsed during time intervals when subject movement is detected beyond the said value or within the said range. In particular, the said characteristic may comprise the amplitude and/or frequency of a repetitive movement.

The method may include the steps of attaching to a subject's body a base on which is rotatably mounted a rotor, deriving a movement-detection signal produced by rotation of the rotor during patient movement, and measuring a cumulative total of time elapsed during time intervals when the magnitude of the movement-detection signal exceeds a predetermined threshold level. In one form, the method may include the steps of generat ing a signal representative of the passage of real time, and summing the value of the real time signal during the said time intervals. In an alternative form the method may include the steps of generating a movement-record signal during the said time inter vals and summing of the value of the movement record signal to give a measure of the said cumula tive total of time elapsed.

The various method aspects of the invention set out above are particularly applicable in measuring patient movement during scratching, but are also applicable in the broader field of measurement of movement other than patient movement, for examplea measurement of vibration in vehicle cabs, and other industrial applications.

Considering now preferred features of the invention in both the apparatus and method aspects, it is preferred that the said rotor is constituted by a rotor of an electro-magnetic stepper motor formed with an extension extending from the axis of rotation to provide the required arrangement of centre of gravity, and that the said detection means for deriving an electrical movement-detection signal is constituted at least in part by the coils of the stepper motor. Thus the steppermotorin such an application is used as a generator and the said electrical movementdetection signal is obtained from output terminals of the stepper motor during rotation of the rotor of the stepper motor.

By a stepper motor is meant an electro-magnetic rotary device capable of use as a motor or a generator which when used as a motor provides rotation of the rotor in discrete steps in response to passage of electric current through motor drive coils.

When such a motor is used as a generator, rotation of the rotor produces discrete electrical output pulses from the coil connections as the rotor moves through discrete steps of movement. The use of a stepper motor in the present invention is particularly advantageous in that the rotor is at least partially locked to the said discrete positions by the effect of the motor coils when at rest, and therefore only moves in response to movement of the base when the base movement exceeds a threshold level set by the mechanical and electrical arrangements of the motor. This effect prevents continued spinning of the rotor after the initiating movement of the base has ceased.The said threshold levels referred to above may constitute the electromagnetic threshold setty the motor itself, or may comprise further higherthresholds set in relation to the amplitude and/or frequency of the electrical output signals of the stepper motor.

According to the present invention in a particularly preferred aspect there is provided apparatus for measuring repetitive movement comprising a rotor rotatably mounted on a base, the rotor having its centre of gravity spaced from its axis of rotation for producing rotary movement of the rotor during translational movement of the base, detection means for deriving an electrical movement detection signal produced by disturbance of a magnetic field by rotation of the rotor, and output means for producing in response to the electrical movement-detection signal an output signal rep resentative of a cumulative total of time elapsed dur ing time intervals when the magnitude of the electri cal movement-detection signal is greater than a pre determined threshold value.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. lisa block circuit diagram of apparatus for detecting movement embodying the present invention; Fig. 2 is a plan view of a physical embodiment of the movement measuring apparatus shown in Fig. 1, the apparatus being housed in a watch casing, and the view showing the apparatus with the watch case back removed; Fig. 3 is a diagrammatic side view of a rotor for use in the apparauts of Figs. 1 and 2; Figs. 4 and 5 are diagrammatic representations respectively of a solenoid device for controlling movement of a balance wheel (of the apparatus shown in Fig. 2), and of the point of contact of the control arm of the device;; Figs. 6 and 8 are circuit diagrams showing examples of means of carrying out the block circuit diagram of Fig. 1; Fig. 7 is a calibration graph suitable for use with the apparatus shown in the preceding figs; Figs. 9 and 10 are plan and side views respectively of a modified movement detector suitable for use in the apparatus of the preceding figures; Fig. 11 is a circuit diagram showing use of the detector of Figs. 9 and 10; and Fig. 12 shows exemplary outputs of the movement detector of Figs. 9 and 10.

Referring firstly to Figures 1 and 2, an electromagnetic stepper motor 11 has conventional stepper motor coils 12 and a rotor 13 with an arm 14 extending from the axis of rotation of the rotor at right angles to the axis. The stepper motor is mounted on a printed circuit board housed in a casing 15 conveniently provided by a casing of a wristwatch. Thus the rotor 13 is rotatably mounted relative to the printed circuit board, and to the casing 15.

The stepper motor 11 is used as a generator to produce electrical signals in response to rotary movement of the rotor 13 which occurs when the watch casing 15 is moved by the wearer of the casing. The output signals from the stepper motor 13 are fed to a high gain amplifier 16 which passes the amplified signals to a retriggerable monostablecir- cuit 17. An example of the signal produced by the amplifier 16 is shown in an inset wave form 1 in Figure land constitutes a movement-detection signal produced by detection means comprising, in this embodiment, the amplifier 16 and the output elements of the stepper motor 11.

There is also fed to the retriggerable monostable circuit 17 a reference voltage from an adjustable voltage reference circuit 18, the reference voltage V ref being shown in an insetwave form 2 in Figure 1. The monostable circuit 17 is arranged to produce an output signal of uniform pulses in response to the movement detection signal 1 when the amplitude of this signal exceeds a variable pre-determined threshold level set by the reference voltage of V ref.

An example of the output signal from the retriggerable monostable circuit 17 is shown in the inset wave form 3 in Figure 1.

The output of the monostable circuit 17 is fed to an actuator indicated generally by the reference numeral 19 and having a coil 20 in parallel with a capacitor 24 of 47 to 100 ssF. The actuator is also shown diagrammatically in Figure 4, the coil 20 being mounted on the circuit board and being arranged to move a spring arm 22 when driven by current through the coil 20. As has been mentioned, the base 15 is consituted by the casing of a conventional wrist watch and certain elements of the wrist watch remain in the casing and are used in the apparatus for measuring movement. As shown diagrammatically in Figure 5, the balance wheel 23 of the watch remains in the casing 15, and a spring arm 22 is arranged to touch lightly against the balance wheel 23 when the spring arm 22 is at rest.When the actuater coil 20 receives current from the monostable circuit 17, the coil 20 effects movement of the spring arm 22 to hold the spring arm off the balance wheel 23 while the current flows. The wrist watch casing 15 contains all the normal components of the watch so that when the spring arm 22 is held off the balance wheel 23 by the actuator coil 20, the watch runs normally and passage of real time is recorded by the watch. When no current passes through the actuator coil 20, the spring arm 22 prevents normal operation of the watch and no time is recorded.

Reference will now be made to Figure 6 which shows by way of example a circuit diagram showing one way of putting into effect the block circuit diagram of Figure 1. The circuit of Figure 6 is composed of nine resistors indicated by reference characters R1 to R9, three capacitors indicated by reference characteris C1 to C3, and two amplifying elements Al and A2 which may for example be elements manufactured by motorola/National under the code number 1776. The numbered terminals shown in the Figure in relation to the amplifying elements Al and A2 are the code numbered terminals of the elements 1776.

The elements forming the circuit of Figure 6 are connected as shown between an input terminal 25 (indicated in Figure 1 as an input terminal 25 of the amplifier 16), and an output terminal 26 (indicated in Figure 1 as an input terminal 26 ofthe actuator 19).

The capacitor C3 in Figure 6 may conveniently constitute the capacitor 24 shown in Figure 1. Drive vol tages to the circuit of Figure 6 are provided at terminals 27 to 32, the potential at terminals 27,28 and 29 being +Ve and the potential at terminals 30, 31 and 32 being -Ve. On Figure 6 there are shown suitable values for the components, the numbers against the resistors being in ohms (for example 100k = 100k ohm). The resistor R6 is an adjustable 1k ohm resistor. By way of example the voltage +Ve may be 1.5 volts and the voltage -Ve may be 1.5 volts. The characteristics of the cells providing the voltages should for example be capable of providing a quiescent current of 5 microamps for 0.12 mA/hours per day and a current of 500 microamps for 1 hour per day, ie 0.5mA/hours per day.This gives a total of 0.62 mA/hours per day so that using say a 75 mA/per hour cell, the total number of days running time would be 4.3 months. Similarly the voltage providing the voltage -Ve should for example be capable of providing a quiescent current of 7 microamps giving a total of 0.1 68mA/hours per day, and an operating current of 500 microamps for 1 hour per day, i.e.

0.5 mA/hours per day, giving a total of 0.668 mA/hours per day. Using for example a 75mA/h hour cell the total days running time would be 4 months.

Relating the exemplary circuit of Figure 6, to the block circuit diagram of Figure 1, a summing point is formed at the junction of the resistor R7 and the capacitor C1 which is the equivalent of the feeding of the wave forms 1 and 2 in Figure 1 to the retrigger able monostable circuit 17. The second stage of the circuit of Figure 6, commencing at the input to the amplifying device A2, will not trigger unless the positive output from stage 1 exceeds the negative potential at the R7/C1 junction. The voltage preset by the variable resistor R6 and the fixed resistor R5 adds a DC level to the AC signal from stage 1 arriving atthe summing point of the junction C1/R7.The overall sensitivity of the apparatus can be adjusted by choosing an appropriate length of arm 14 on the rotor 13 (as shown in detail in Figure 3) and a fine variation of the sensitivity can be achieved by raising or lowering the base line of the input signal to stage 2 of the circuit of Figure 6 by varying the variable resistor R6. Increasing the reference voltage Vref by changing the variable resistor R6 decreases the sensitivity.

When the level of the movement detection signal (1) exceeds the reference Vref threshold of the wave form (2), the monostable circuit 17 is triggered and will remain on until the movement detection signal (1) falls below the reference voltage Vref. The pulse width of the output from the monostable circuit 17 is very short and is therefore running at a high frequency. There are several output pulses produced for every one input pulse that exceeds the reference voltage Vref. This means that hysteris is and therefore accumulative error of the system is negligible.

The output at the terminal 26 is fed to the actuator 20 which in turn controls the running state of the balance wheel 23. Thus the actual time during which movement of the watch casing is taking place is stored and is displayed directly on the watch. The graph in Figure 7 shows the correlation factor between the scratch time occurring in medical use of the apparatus, and the machine time recorded by the watch. The factor in the example shown is 0.9995 Conveniently the motor used may be a small two pole stepper motor used as an AC generator, and the output of the stepper motor is amplified by the gain amplifier 16. The effect of the monostable circuit 17 is to compare the amplified output of the stepper motor with a reference voltage which acts as a threshold for the level or degree of movcment amplitudeto be monitored.If the movement detection signal exceeds the threshold voltage, then stage 2 of the circuit is triggered for the duration that the input is above the threshold.

The effect of the capacitor C3 on the output of stage 2 of the circuit in Figure 6 (capacitor 24 in Figure 1) is to integrate the output pulses from the retriggerable monostable circuit 17 and to drive the actuator 19 to control the balance on the mechanical watch.

Figure 8 shows a circuit diagram of a modification of the circuit of Figure 6 for use with a L.C.D. watch.

Only stage 2 of the circuit of Figure 6 is shown in Figure 7, and the modification consists of the removal of the 100 micro F capacitor C3 and insertion of a diode D1 between the output of the amplify ing device A2 and an output terminal 33. The output at the terminal 33 may be connected to drive the oscillator of the L.C.D. watch and a quartz analogue watch may be controlled in the same way. The diode D1 is normally forward biased and the watch oscil lator is inhibited. When the reference voltage Vref is exceeded, stage 2 of the circuit of Figure 8 is triggered and the diode DR is reversed biassed. In this state the watch oscillator runs and reel time is recorded on the watch.

Practical point to be noted in the construction of the embodiments described include the following.

Where the movement measuring apparatus is to be used for measuring leg limb movements in patients,, the detector stepper motormust be very firmly mounted and the arm of the motor rotor must be soldered to the motor piniont as the thrust of a human leg during patient movement is powerful enough to dislodge these mounting points unless special care is taken. Similarly the batteries must be very firmly mounted.

Of the versions described the most accurate and reliable have been found to be the all electronic L.C.D. and quartz analogue versions, the main reason being that the mechanical watch version relies upon the balance wheel being capable of starting from any position. The electronic versions do not have this problem. A factor against the L.C.D. watch version is the difficulty in setting the watch to time when compared to the simple pattern system on a mechanical watch. Overall the movement measuring apparatus described provides a cheap and very sensitive means for detecting movement and vibration.

When used in the medical field for measurement of scratch movement on patients, the apparatus is capable of measuring scratch movement in a widely varying range direction and velocity, and is responsive to scratch movement in all planes. Calibration is simply achieved by setting the comparator threshold voltage. The instrument provides a direct recording of the cumulative time spent moving by the patient.

In such use, before the patient goes to sleep the movement meters (which are little largerthan a wrist watch) are attached to each wrist and ankle with a rubber strap and a "velcro" fastener. The meters are removed on waking. The time the meters are worn and the elapsed time on each meter are recorded.

Most patients are able to perform this simple procedure unaided. The sensitivity of the limb meters can be assessed by measuring their response to simulated mild scratching for 1,2 and 3 minute periods (for example in a number of normal subjects). There is found to be a direct relationship between the duration of scratching and the recorded time on the limb meter.

A number of modifications of the apparatus shown are also possible. For example the apparatus may be used to permitthe measurement of vibration. Also the output from the detecting and measuring circuits can be stored in analogue form to be read later on a central reader. This would dispense with the need to link the meter to a watch, and would make the worn apparatus even smaller. Where the apparatus is used for measuring vibrations, for example in industrial applications, the circuitry can be modified to count and store the number of times a predetermined vibration rate and/or amplitude are encountered.

It is to be appreciated that in the embodiments described, the time elapsed is measured by the movement of the hands, and not by the date change mechanism described with regard to the prior art.

Indeed the change of sensitivity of the watch during the date change operation is such that the movement measuring apparatus should not be used during the date change part of the watch operation.

There will now be described a modified embodiment of the invention, with reference to Figures 9 to 12 of the accompanying drawings. The modification consists of the replacement of the stepper motor and elongated arm shown in Figures 1,2 and 3 (which in the previous embodiment constituted the movement detection means), by a different form of movement detection means in which a quantity of mercury is used as an electrically conductive medium and is sealed in a container in which it is movable to bridge various electrical contacts, upon the movement of the detection means which is to be detected.

Referring to Figures 9 and 10 a predetermined quantity of mercury 34 is sealed between two circular, equal diameter, plates 35 of non-conductive material, and a circumferential outer wall 36 made of steel shim. Close to the outer perimeter of the discs 35 are mounted a series of brass rods 37 which extend between the plates 35 perpendicular thereto.

The rods 37 are isolated from one another by the plates 35, but are wired together by two wires 38 and 39 each of which is connected to alternate pins around the perimeter of the device. Thus the pins are wired together in sequences 1-3-5-7-9 etc and 2-4-6-8-10 etc. Therefore any individual rod 37 is not connected to the immediately adjacent rods. The amount of mercury 34 sealed into the container is carefully calculated, by empirical testing, to arrive at a suitable sensitivity of the detector. If the amount of mercury is too large or too small, the sensitivity of the detector is greatly reduced.

Referring to Figures 11 and 12, the detector, which is referred to generally as 11', is mounted in the lower half of a potential divider formed by a resistor 40 and leads 41 42 and 43. If an AC or DC signal is applied across input terminals 43 and 44 of the potential divider, an output taken atterminals45 and 46 will vary with movement of the mercury 34 in the detector 11'.

Figure 12 shows diagrammatically two forms of output which may be obtained. The detector may be regarded as working in one of two modes. Thus the detector may be regarded as producing a varying resistance depending upon the position of the mercury 34 around the perimeter of the detector 11', so that the voltage across the detector 11' varies. In another mode, due to the poor contact between the mercury and the contactors, noise of varying amplitude and duration is produced upon movement of the mercury. In either mode, an output signal is obtained which may be fed, if necessary with further processing, to the circuits shown in the preceding Figures, by substituting the movement detector 11' for the movement detector 11 previously shown.

Claims (19)

1. Apparatus for measuring movement comprising detection means for detecting movement having a characteristic beyond a predetermined threshold value or in a predetermined range of values, and output means for measuring a cumulative total of time elapsed during time intervals when movement is detected by the detection means beyond the said value or in the said range.

2. Apparatus according to Claim 1 in which the said characteristic consists of an amplitude and/or frequency of a repetitive movement.

3. Apparatus according to Claim 1 or 2 in which there is provided a rotor rotatably mounted on a base, the rotor having its centre of gravity spaced from its axis of rotation for producing rotary movement of the rotor during transational movement of the base, and in which the said detection means is arranged to detect the said movement by deriving an electrical movement-detection signal produced by disturbance of a magnetic field by rotation of the rotor, and the output means is arranged to produce in response to the electrical movement-detection signal an output signal representative of a cumulative total of time elapsed during time intervals when base movement is detected, by the detection means, having a characteristic beyond a predetermined value or in a predetermined range of values.

4. Apparatus according to Claim 3 in which the said time intervals are intervals when the magnitude ofthe electrical movement-detection signal is greaterthan a predetermined threshold.

5. Apparatus for measuring movement comprising a rotor rotatably mounted on a base, the rotor having its centre of gravity spaced from its axis of rotation for producing rotary movement of the rotor during translational movement of the base, detection means for deriving an electrical movementdetection signal produced by disturbance of a magnetic field by rotation of the rotor, and output means for producing in response to the electrical movement-detection signal an output signal representative of a parameter of the movement of the base.

6. Apparatus according to Claim 5 in which the said parameter of the base movement is a cumulative total of time elapsed during time intervals when base movement is detected, by the detection means, having a characteristic beyond a predetermined threshold value or in a predetermined range of values.

7. Apparatus according to Claim 6 in which the said characterisitc consists of an amplitude and/or frequency of a repetitive movement.

8. Apparatus according to Claim 6 or7 in which the said time intervals are intervals when the magnitude of the electrical movement-detection signal is greater than a predetermined threshold.

9. Apparatus for measuring repetitive movement comprising a rotor rotatably mounted on a base, the rotor having its centre of gravity spaced from its axis of rotation for producing rotary movement of the rotor during translational movement of the base, detection means for deriving an electrical movement detection signal produced by disturbance of a magnetic field by rotation of the rotor, and output means for producing in response to the electrical movement-detection signal an output signal representative of a cumulative total of time elapsed during time intervals when the magnitude of the electrical movement-detection signal is greater than a predetermined threshold value.

10. Apparatus according to any of Claims 3 to 9 in which the said rotor is constituted by a rotor of an electromagnetic stepper motor formed with an extension extending from the axis of rotation to provide the required arrangement of centre of gravity, and in which the said detection means for derving an electrical movement-detection signal is constituted at least in part by the coils of the stepper motor.

11. Apparatus according to any preceding Claim adapted to be secured to a limb of a subject whose movements are being examined, in which the said base comprises a housing for the rotor provided with fastening means for fastening the base to a limb of the subject.

12. A method of measuring movement of a subject under examination, comprising the steps of detecting subject movement having a characteristic beyond a predetermined threshold value or swithin a predetermined range of values, and measuring a cumulative total of time elapsed during time intervals when subject movement is detected beyond the said value or within the said range.

13. A method according to Claim 12 in which the said characteristic comprises the amplitude and/or frequency of a repetitive movement.

14. A method according to Claim 9 or 10 including the steps of attaching to a subject's body a base on which is rotatable mounted a rotor, deriving a movement-detection signal produced by rotation of the rotor during subject movement, and measuring a cumulative total of time elapsed during time intervals when the magnitude of the movementdetection signal exceeds a predetermined threshold level.

15. A method according to Claim 12, 13 or 14 including the steps of generating a signal representative of the passage of real time, and summing the value of the real time signal during the said time intervals.

16. A method according to Claim 12, 13 or 14 including the steps of generating a movementrecord signal during the said time intervals and summing the value of the movement-record signal to give a measure of the said cumulative total of time elapsed.

17. A method according to Claim 12, 13, 14, 15 or 16 when consisting of a method of measuring patient movement during scratching.

18. Apparatus for measuring movement substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of measuring movement of a subject under examination substantially as hereinbefore described with reference to the accompanying draw ings.