COMBINED MOTOR DRIVE AND CONTROL DEVICE

Abstract: An electronic system comprises a power amplifier (1) with antiphase outputs for driving an actuator/transducer assembly. An error conditioning and converter stage (2) provides input to the power amplifier (1). A transducer excitation function generator (3) provides periodic signals of controlled amplitude and phase for combination with the input signals to the power amplifier (1). An input signal converter circuit (4) transforms the position command supplied to the system to a suitable form for feeding a summation circuit, which derives a position error signal. A pre-amplifier (5) takes the position measurement signal and supplies it to a second input of the summation circuit.

Description: COMBINED MOTOR DRIVE AND CONTROL DEVICE The present invention relates to means for driving and controlling an electric motor Particularly, but not exclusively the invention relates to means for driving and controlling a linear electromagnetic motor, which comprises an integral position measurement system providing information on the output movement produced and enabling servo position control. A motor of this type is described in a prior GB Patent Application 9517603.8. The control electronics required by such motors must provide power drive to the device, in order for it to produce mechanical output power, and must simultaneously provide precision excitation signals for the integral position measurement system In addition a means of extracting and signal conditioning the resultant position signal and for implementing the servo control loop is required. The performance, efficiency, and cost of manufacture of systems employing such actuators is critically dependent on the concept and design ofthe associated drive and control electronics. Figure 1 of the accompanying drawing shows a linear motor and integral position measurement system of the type to which this invention is particularly relevant, and figures 2a, 2b and 2c show the equivalent circuit or electrical schematic representations ofthe motor. The figures show the motor to consist basically of two or four inductive circuit elements which are connected in a half bridge according to figures 2a and 2b or full bridge configuration as in figure 2c. DC or quasi-static DC drive voltage is applied across the bridge in combination with a superimposed steady state AC excitation signal to provide energization for the position measurement function The resultant position signal appears as a single ended output at the node of the half bridge circuit or as a differential output at the mid point of the full bridge configuration. Imbalance of the bridge is bought about by movement of the magnet and pole piece assembly - which creates differential incremental changes in the inductance of the windings. As described in GB Patent application 9517603.8, interconnection of the windings is arranged such that the forces produced on the magnet assembly by current flow in the coils contribute in unison, whilst the incremental changes in inductance are lumped according to their sign in the relevant arms ofthe half bridge or full bridge circuits The present invention sets out to provide a combined power drive, transducer excitation and signal conditioning system and position control loop, which performs simultaneously to maximise the overall electromechanical efficiency of the system and to realise the capabilities ofthe integral position measurement ofthe actuator According to the invention there is provided an electronic system, comprising a power amplifier with antiphase outputs for driving the actuator/transducer assembly, a pre¬ amplifier for receiving output signals from the actuator/transducer assembly, an input command signal, and an excitation and signal conditioning circuit which functions to combine the outputs of the pre-amplifier, the input command signal, and a periodic excitation signal to provide input signals to the power amplifier for driving the actuator/transducer assembly. The excitation and signal conditioning circuit may comprises an error conditioning and converter stage, which provides input to the power amplifier and a transducer excitation function generator, which provides periodic signals for combination with the input signals to the power amplifier. Preferably the excitation and signal conditioning circuit includes a stage which transforms the input command signal supplied to the system to a suitable form for feeding a summation circuit, which derives a position error signal; and that the pre¬ amplifier supplies the actuator/transducer output signal to a second input of the summation circuit. The power amplifier may be a switching power amplifier The input command signal may be converted to a proportional AC signal before being compared with a position feedback signal, alternatively the actuator/transducer output signal may be converted to a proportional DC signal and compared directly to the input command signal. The input signals provided to the power amplifier are preferably in the form of a pulse- width modulated representation which may be modified by adding a digital advancing/retarding technique to achieve a synchronous perturbation component The error conditioning and conversion circuit may also comprise a synchronous detector, for demodulating incoming position error information using a synchronous reference signal provided by the said transducer excitation function generator, a servo loop compensation stage, for receiving a signal from the synchronous detector and responding to the DC component thereof by providing the compensation necessary for the desired position control loop characteristic; a converter stage, for converting a compensated DC error signal received from the servo loop compensation stage to a PWM signal, having period T; and a digital modulator for applying advance and retard to the PWM signal received from the converter stage, to produce a modulation having a period 2T. The power amplifier may also be a linear amplifier and substantially sinusoidal perturbation signals may be employed to energise the actuator transducer assembly. Preferably the excitation and signal conditioning circuit includes a stage which converts the input command signal to balanced complementary DC reference signals which are proportional in amplitude to the input command signal and a first synchronous demodulator which receives respective signals from the amplifier and also receives a synchronous reference potential and produces DC outputs in proportion to the synchronous component of the AC energising signal in the respective amplifier outputs. The excitation and signal conditioning circuit may also comprise first summing means for summing the respective outputs ofthe said first synchronous demodulators with the said balanced complementary DC reference signals to form error signals and compensators for performing control loop compensation on the respective error signals associated with the synchronous perturbation component of the power amplifier output. In a first and second preferred embodiment of the invention, the transducer excitation function generator and power amplifier are implemented using switching techniques, this offering high efficiency and drive power, and the signal conditioning processes are hybrid - that is they employ mixed analogue and switching technology. In two further embodiments of the invention, a linear power amplifier is employed and steady state sinusoidal or near sinusoidal transducer excitation is used. In these embodiments much ofthe signal processing is linear although certain hybrid techniques are utilised. These further embodiments offer the potential for greater precision of performance ofthe overall system, but lack the benefits of efficiency, compactness and relatively low cost of manufacture ofthe preferred embodiments. The invention will be further described by way of these exemplary embodiments and with reference to the accompanying drawings in which: Figure 1 is a cross sectional diagrammatic view of a combined linear electric motor and position measurement system with which the present invention can be used; Figures 2a, 2b and 2c show electrical schematic circuits ofthe system of figure 1 , Figure 3 is an overall block schematic diagram of the electronic system in accordance with the present invention arranged for achieving power drive, position measurement and position control ofthe motor of figure 1; Figure 3 a is an overall block schematic diagram of a first preferred embodiment of the electronic system in accordance with the present invention employing a switching power amplifier and digitally derived transducer excitation signals Figure 3b is an overall block schematic diagram of a second preferred embodiment of the electronic system in accordance with the present invention employing a switching power amplifier and digitally derived transducer excitation signals Figure 4 is a schematic representation of a switching implementation of the power amplifier of figures 3a and 3b, for providing power drive and transducer excitation for the system of figure 1; Figure 5 is a timing diagram showing the means for achieving transducer excitation in the electronic systems of figures 3 a and 3b by the use of digital modulation of the power amplifier input signal; Figure 6a is a block schematic diagram showing the principal sub-systems of the error signal conditioning and converter stage ofthe embodiment of figure 3 a, Figure 6b is a block schematic diagram showing the principal sub-systems of the error signal conditioning and converter stage ofthe embodiment of figure 3b, Figure 7 is a block schematic diagram showing the principal sub-systems of a motor energization and position control system defining a third embodiment ofthe invention Figure 8 is a block schematic diagram showing a motor energization and position control system defining an alternative functional arrangement of the embodiment of figure 7 In the general system block diagram of figure 3 an actuator/sensor unit such as that depicted in figure 1 is shown being driven by a power amplifier 1. A single ended position signal e3 and/or differential position signals e4, s derived from the actuator/sensor unit are fed to a pre amplifier 5 which includes a signal converter circuit An input signal converter stage 4 produces a proportional version e6 of the input command signal ein, and the output of the pre-amplifier and signal convener stage 5, es, is subtracted from this. The difference, the position error signal η , is fed to a signal conditioning and conversion stage 2. In this stage the position error signal e7 is demodulated if necessary, compensated, and converted to a signal suitable for feeding to the power amplifier 1. Compensated position error information and synchronous transducer energization are combined in the output of stage 2, the synchronous reference e r ef and digital modulation signals DMOD required in the various embodiments ofthe invention for this purpose being provided by an excitation function generator stage 3. Figure 3 a is a block schematic of a first preferred embodiment of the invention, in which an actuator/sensor unit such as that depicted in figure 1 is shown being driven by a switching power amplifier 1. Single ended position signals e3 or differential position signals e4 , e5 derived from the actuator/sensor unit are fed to the pre amplifier and signal converter stage 5 a . In this first preferred embodiment of the invention, the output of stage 5 a is an AC signal, proportional to the position signal e3 or to the differential position signals e4, es . It may be a filtered version of these signals as shown by the path Pl comprising a pre amplifier 5 a ι and filter 5a2, or it may simply be an amplified version of the signals e3 5 or e4, es as shown by path P2 which features only the pre amplifier 5 a ι . In order for the DC position command signal ein of figure 3 a to be compared with the position feedback signal e8 a , it is converted to a synchronous AC signal eόa This is the function ofthe input signal converter stage 4 a which performs conversion of ej n to a synchronous AC signal eόa using reference signal eref provided by the excitation function generator 3 a . In stage 4 a , signal chopping or multiplying techniques are employed to produce an AC signal proportional in magnitude to the input ei n and proportional in phase to the sign of ein- The frequency of the resultant AC position command signal eόa is equal to that of the position feedback signal e8 a , and the phase, as determined by the synchronous reference e r ef is arranged such that effective differencing of the AC position command signal eόa and the AC position feedback signal e8a can be performed by the summation stage 6 a . The resultant output e7 a of the summation stage 6 a of figure 3a is thus a synchronous AC signal expressing in magnitude the degree of position error yielded by the control loop, and in phase, relative to the reference signal e r ef, the sign of the position error As shown in figure 3a, the position error signal is then fed to the signal conditioning and converter stage 2a, the function of which is to demodulate the AC position error signal, to provide a position error signal suitably compensated for achieving closed loop stability in the position control system, to convert this signal to a pulse width modulated (PWM) representation suitable for driving the switching amplifier 1, and finally to modify this PWM representation such as to add a synchronous perturbation component which serves as energization for the position measurement function of the sensor/actuator unit of figure 1. The block diagram of figure 6a shows the principal sub-systems of the signal conditioning and conversion stage 2 a and of the input signal convener stage 4 a appropriate to the first preferred embodiment of the invention Incoming position error information e7 a is demodulated by the synchronous detector 2 a ι using the synchronous reference signal eref provided by the transducer excitation function generator 3 a (see figure 3), and the resultant signal is fed to the servo loop compensation stage 2&. This stage responds to the DC component of the demodulated signal providing the compensation necessary for the desired position control loop characteristic. Following this, the compensated DC error signal is converted to a pulse width modulated (PWM) signal of period T by converter stage 2 a 3. This signal in turn feeds digital modulator 2 4 which applies synchronous advance and retard to the T period PWM signal to produce a 2T period modulation The necessary digital control signals for this digital modulation. DMOD, are provided by the excitation generator 3 a . In this first preferred embodiment of the invention, the input position command signal ein is converted to a synchronous AC signal in order for it to be summed with the transducer position signal This is shown in figure 6a where the input signal converter stage 4 a is seen to comprise an input buffer amplifier 4 a \ which feeds a chopper or multiplier stage 4-^2 The chopper stage uses reference signal eref to multiply or to chop the input command signal ein to produce an AC signal eόa which is proportional in magnitude to ejn , but modulated by eref such as to allow effective summation of eόa with the position feedback signal e8a at the synchronous frequency 1/2T Figure 3 b is a block schematic diagram of a second preferred embodiment of the invention, in which an actuator/sensor unit such as that depicted in figure 1 is shown being driven by a switching power amplifier 1 Single ended position signals e3 or differential position signals e4, e5, derived from the actuator/sensor unit are fed to the pre amplifier and signal converter stage 5b. In this second preferred embodiment ofthe invention, the output esb of stage 5b is a DC signal proportional in magnitude to the position signal e3 or to the differential position signals e4, es, and in sign to the relative phase of the position feedback signals to the synchronous reference e r ef In this configuration, the converted position feedback signal eδb, being a DC proportional signal, is compared directly to the DC input command signal ein, avoiding the need to convert the command signal ej n to a synchronous AC signal. This further avoids the requirement to demodulate the error signal e7b produced by the summer stage 6 Thus the input signal converter stage 4b is simply a DC buffer amplifier which feeds a scaled version esb ofthe DC input command signal ej n to the summer stage 6 . The resultant output e b of the summer stage 6 of figure 3b is thus a DC signal expressing directly in sign and magnitude the degree of position error yielded by the control loop. As shown in figure 3b, the position error signal is then fed to the signal conditioning and converter stage 2b, the function of which is to provide a position error signal suitably compensated for achieving closed loop stability in the position control system, to convert this signal to a pulse width modulated (PWM) representation suitable for driving the switching amplifier 1 and finally to modify this PWM representation such as to add a synchronous perturbation component which serves as energization for the position measurement function of the sensor/actuator unit of figure 1. The block diagram of figure 6b shows the principal sub-systems of the signal conditioning and conversion stage 2b and of the input signal converter stage 4b appropriate to the second preferred embodiment of the invention. Incoming DC position error information e7b is fed to the servo loop compensation stage 2 l, this stage providing the compensation necessary for the desired position control loop characteristic. Following this, the compensated DC error signal is converted to a pulse width modulated (PWM) signal of period T by converter stage 2 2 This signal in turn feeds digital modulator 2b3, which applies synchronous advance and retard to the T period PWM signal to produce a 2T period modulation. The necessary digital control signals for this digital modulation, DMOD, are provided by the excitation generator 3 . In this second preferred embodiment ofthe invention, the input position command signal ein requires no conversion to a synchronous AC signal in order for it to be summed with the transducer position signal. Thus in figure 6b input signal converter stage 4b is seen to comprise only a DC input buffer amplifier 4b i which feeds the summer 6 Figure 5 is a timing diagram, which shows the way in which the above preferred embodiments ofthe invention employ switch-mode techniques to provide simultaneous power drive and precision transducer excitation for a combined motor and position sensor device such as shown in figure 1 Wave form F ι in figure 5 shows an equal mark/space ratio square wave form such as might be applied to the input of the switching amplifier 1 of figure 3 The amplifier shown in diagrammatic form in figure 4 acts using power semiconductor devices F 1 , F2, F3 and F4 to switch the ends ofthe applied load, in a fashion closely following the switching input wave form e9, between the applied power rails OV, +VE This achieves minimal dissipation in the amplifier 1 and has the benefit that the amplitude of the amplifier output and the relative times ofthe switching transitions of the output are well defined and repeatable. The inductance of the load acts to smooth or average the current flowing and the magnitude of any resultant steady DC component is determined by the mean applied voltage divided by the net load circuit resistance Thus for wave form F] of figure 5, having an equal mark/space ratio, the average DC load current is zero corresponding to a zero input to the amplifier Wave form F2 of figure 5 shows pulse width modulation (PWM) ofthe amplifier input signal, this being achieved in the embodiment of figure 4 by time shifting the rising edge of the wave form, keeping the overall period to T seconds The average DC value of the voltage applied to the load is now non zero and DC current flows in the load Wave form F3 shows PWM modulation, again using the rising edge of the wave form, but this time retarded to reverse the sign of the average current flowing in the load compared to that of wave form F2 This follows already established principles, and it can be appreciated that PWM modulation can be achieved by modulating either transition of the wave form in a discrete (digital) or continuous (analogue) fashion Either method would serve to provide DC or quasi static drive current to the motor system of figure 1 in proportion to the position error or command signal Wave form F4 shows how digital techniques are employed to achieve synchronous PWM modulation of the amplifier drive wave form and hence well-controlled and synchronised AC excitation for the position measurement function Here digital modulation techniques are used alternately to advance and retard a given transition of the PWM wave form by a fixed fraction of the PWM period T This has the effect of alternately offsetting the mean drive voltage applied to the actuator by a con αnt fraction and at a constant frequency The period of this applied perturbation is exactly twice that ofthe pulse width modulation associated with the quasi-static signal and the phase relative to a given rising or falling transition of the reference wave form F i is constant. These conditions are ideal for recovery of the transducer signal since the PWM modulation associated with DC or quasi static current is of period T whilst the excitation source for the position measurement, and hence the position information, is conveyed by the magnitude and relative phase of a signal of period 2T Using synchronous demodulation techniques, the component due to the DC modulation at period T is automatically suppressed, allowing precision recovery of the position information despite the presence of the relatively large higher frequency PWM components. This is illustrated by further reference to wave form F7, which is the result of synchronously sampling wave form F4 with the 2T period function wave form Fό Wave form F4 carries no DC component, but is digitally modulated with a 2T period peπurbation component. Synchronous sampling acts to multiply the wave form by a synchronous reference, in this case wave form Fό, which, given the correct relative phase relationship, acts to demodulate the synchronous component and yield a DC- proportional component in the resultant wave form. In the example of wave form F7, the resultant has a net positive DC component of fraction 1/8 ofthe peak amplitude. Wave form F8 further shows how the detection method rejects the higher frequency PWM components carrying the DC or quasi-static signal to the system. Here wave form F5, which carries both 2T period perturbation and T period PWM modulation, is synchronously sampled by wave form Fό, the resultant being wave form F$ Although more complex, the average is the same as that of wave form F7 , this being contributed solely by the 2T period component ofthe wave form F5 Thus the perturbation or transducer excitation signals are applied using digital techniques to achieve precise, repeatable and highly synchronous position signals, and the DC or power drive signals are applied as additional pulse width modulation using either analogue or digital techniques. It can be appreciated that suppression of the higher frequency T period PWM components, achieved by the use of synchronous demodulation, is effective for all perturbation functions with periods being a binary multiple of T Figure 7 shows a second embodiment of the invention in which a complementary output linear power amplifier 1\ is employed to drive the actuator / sensor unit The amplifier provides quasi static DC output voltage or cunent to provide power drive to the actuator/sensor unit, and superimposed sinusoidal or near sinusoidal functions for the AC energising signals. In this embodiment the amplitudes of the AC energising voltages driving the actuator/sensor unit are independently controlled in local closed loop feedback systems, this operating the position sensing system of the actuator / sensor unit in a high precision null balance mode. Referring to figure 7, the outputs e7i , e72 of amplifier 1\ drive the actuator sensor unit which is configured either as a half bridge or full bridge circuit producing the corresponding single ended position output signal e73 or the differential position output signals e74 , e75. These position output signals are fed to a preamplifier stage 7] o which produces a single ended position output signal e76 The amplifier outputs e7i , e72 , in addition to driving the actuator sensor unit, are also fed to stages 73 and 74 , these being synchronous demodulators which, in conjunction with the synchronous reference potential eref . produce DC output signals e79 , e7io which are in exact proportion to the synchronous component of AC energising signal in the amplifier outputs e7i , e72- These potentials are summed with reference signals e7i5 , e7i6 which are derived from the position command signal ej n by an input signal converter stage I9. The stage 79 acts to convert the command signal ejn to balanced complementary DC outputs e7is , e7iό which are proportional in amplitude to ein but of opposite sign and superimposed on a constant component of voltage. Signals e7π , e7i2 are the enor signals or the deviations of potentials e79 . e7io from the commanded values derived from ei These error signals are fed to stages 75 , 7ό which perform control loop compensation to achieve the desired response of amplitude control of the AC energising component of signals e71 , e72 Following compensation, the outputs of stages 7s , 7ό are fed to voltage controlled function generators 77 , 7s which produce sinusoidal or near sinusoidal output voltages e7i3 , e7i4 which are synchronous with the switching reference eref and proportional in amplitude to the outputs of the compensation stages 75 , 7ό The outputs of function generators 77 , 7s are summed into the inputs of amplifier 71 to complete the closed loops in which the AC energising components of the actuator sensor drive potentials e7i , e72 are controlled. The AC energization component of the actuator sensor potentials are thus anti phase sinusoidal or near sinusoidal functions which are controlled to vary in amplitude, in a complementary fashion, in proportion to the magnitude and sign of the control system input command signal ein In order to provide for position sensing and control in mid range when ej n is zero, an offset or constant magnitude component is added to the energising potentials. As mentioned above this component is introduced by an input convener stage 79 in figure 7 Returning to figure 7. It will now be evident that the signal e7ό appearing at the output of pre amplifier 1 \Q is a position error signal. The controlled amplitude AC energising potentials produced by the local control loops described above are summed by the inductive bridge circuit ofthe actuator unit and, given that the relative imbalance of the energising potentials corresponds to the relative imbalance of the actuator bridge inductances (brought about by movement of the actuator), then the position output signal e73 or e74 , e75 from the sensor/actuator is of null amplitude. To implement closed loop position control of the actuator sensor unit the pre amplified null error signal e76 is fed to a synchronous demodulator stage 1\ Using the synchronous reference eref this stage produces a DC output e77 which is proportional in magnitude and sign to the AC error signal e7ό. This in turn feeds control loop compensation stage 712 which acts on the enor signal e77 to provide the desired response characteristics for the overall servo position control function. The position control loop is completed by splitting the compensated position enor signal e78 into complementary outputs via amplifiers 1\ 3 , 714 and summing these signals with the AC energising inputs e7i3 , e7i4 into the power amplifier 7] . The benefit of the null balance control loop described above is that for all output positions of the actuator unit according with the commanded position represented by signal ein , the position output signals e73 or e74 , e75 produced by the actuator unit are null. This means that precision of signal processing in the position control loop is not required. Figure 8 shows a third embodiment of the invention which is a modification of the configuration depicted in figure 7. In this embodiment the AC energising voltages driving the actuator/sensor unit are maintained at constant amplitude with the result that the feedback signals from the sensor ponion of the unit correspond to absolute position and not to position error as in the system of figure 7 described above This anangement has the benefit of reduced overall complexity and hence cost, but lacks the precision of operation attainable from the system of figure 7 Referring to figure 8, the outputs of amplifier 81 drive the actuator/sensor unit producing a single ended position output signal e83 or differential position output signals e84, e85. These position signals are fed to a pre amplifier stage 810 which in turn feeds a demodulator stage 811. The demodulator stage, using the synchronous reference signal e r ef converts the AC position feedback signal eδό to a DC signal e87, the magnitude of which is proportional to e86, and the sign being determined by the phase of e86 relative to that of the reference e re f. To achieve position control, the demodulated position feedback signal e87 is compared with a buffered version ess of input command signal ej n by the summation stage 85. The resultant position error signal e89 is fed to the stage 8ό which provides the necessary compensation of the error signal for the required overall position control loop response. This compensated enor signal e810 then feeds the power amplifier via an additional summer and driver stages 87, 88 and 89. The additional summer stage 87 functions to allow injection of the transducer excitation function es 11 into the power amplifier 81. This is a periodic sinusoidal or near sinusoidal function produced by stage 84. This function emerges from stage 87 summed with, and hence superimposed upon the position enor signal esiO This composite signal e815 is converted to balanced antiphase signals by the stages 8s, 89 where it drives the inputs ofthe power amplifier 8] . The outputs of this amplifier e% \ , eg2 thus contain balanced or differential drive components of both the power actuation and transducer energization signals required by the actuator/sensor unit. The function of the energization control loop described here is to stabilise the amplitudes of the transducer energization component of the actuator/sensor drive signals to a degree adequate for the required position accuracy and repeatability To achieve this, the outputs esi, es2 of the amplifier 8] are fed to stage 83 which performs demodulation of the perturbation component of esi, es2 using the synchronous reference signal e re f. The stage 82 responds to the difference of signals e 81 ' e 82 tnus ensuring that the overall amplitude of the energization applied to the actuator/sensor unit is taken into account. The output esi 2 of stage 82 is a DC signal proportional in magnitude to the synchronous component of the difference between es 1 and eg2 which is compared with a DC reference potential Vref in the summer stage 813. The resultant error signal esi 3 feeds stage 83 which provides the compensation required to achieve the desired response characteristic of the excitation signal stabilisation loop. The compensated DC output, ej 84 then feeds the function generator stage 84. This stage, using the synchronous reference signal, e re f, produces a sinusoidal output wave-form approximately proportional in amplitude to the compensated DC input esi4 and controlled in phase, or synchronous with, the reference e re f

Claims: CLAIMS 1. An electronic system, comprising a power amplifier (1, l 8ι) with antiphase outputs for driving the actuator/transducer assembly, a pre-amplifier (5, 7-o, 8j 0 ) for receiving output signals from the actuator/transducer assembly, an input command signal, and an excitation and signal conditioning circuit which functions to combine the outputs of the pre-amplifier (5, 7 ]0 , 8ιo), the input command signal, and a periodic excitation signal to provide input signals to the power amplifier (1, 7], 8 t ) for driving the actuator/transducer assembly. 2 An electronic system according to claim 1, characterised in that the excitation and signal conditioning circuit comprises an error conditioning and converter stage (2), which provides input to the power amplifier (1) and a transducer excitation function generator (3), which provides periodic signals for combination with the input signals to the power amplifier (1). 3. An electronic system according to claim 1, characterised in that the excitation and signal conditioning circuit includes a stage which transforms the input command signal supplied to the system to a suitable form for feeding a summation circuit (6), which derives a position error signal; and that the pre-amplifier (5) supplies the actuator/transducer output signal to a second input ofthe summation circuit (6). 4 An electronic system according to Claim 1 wherein the power amplifier (1) is a switching power amplifier. 5. An electronic system according to Claim 1 , wherein the input command signal is DC and is converted to a proportional AC signal before being compared with a position feedback signal. 6 An electronic system according to Claim 1, wherein the actuator/transducer output signal is converted to a proportional DC signal. 7 An electronic system according to Claim 4, wherein the input signals provided to the power amplifier (1) are in the form of a pulse-width modulated representation 8 An electronic system according to Claim 7, wherein the pulse-width modulated representation is modified by adding a digital advancing retarding technique to achieve a synchronous perturbation component. 9 An electronic system according to Claim 6, wherein the actuator/transducer output signal, following conversion to a proportional DC signal is compared directly to the input command signal ein 10 An electronic system according to Claim 5, wherein the enor conditioning and conversion circuit comprises: a synchronous detector, for demodulating incoming position error information using a synchronous reference signal provided by the said transducer excitation function generator; a servo loop compensation stage, for receiving a signal from the synchronous detector and responding to the DC component thereof by providing the compensation necessary for the desired position control loop characteristic, a convener stage, for converting a compensated DC error signal received from the servo loop compensation stage to a PWM signal, having period T, and a digital modulator for applying advance and retard to the PWM signal received from the converter stage, to produce a modulation having a period 2T 1 1 An electronic system according to Claim 1 , characterised in that the power amplifier (7ι, 8j) is a linear amplifier. 12 An electronic system according to claim 1, characterised in that substantially sinusoidal perturbation signals are employed to energise the actuator transducer assembly 13 An electronic system according to Claim 1, characterised in that the excitation and signal conditioning circuit includes a stage which converts the input command signal to balanced complementary DC reference signals e,,« e-, 6 which are proportional in amplitude to the input command signal e m 14 An electronic system according to Claim 13, characterised in that the excitation and signal conditioning circuit includes at least one first synchronous demodulator 7, , li which receives respective signals from the amplifier and also receives a synchronous reference potential er e f and produces DC outputs in proportion to the synchronous component ofthe AC energising signal in the respective amplifier outputs 15. An electronic system according to Claim 14, characterised in that the excitation and signal conditioning circuit comprises first summing means for summing the respective outputs of the said first synchronous demodulators with the said balanced complementary DC reference signals to form error signals. 16. An electronic system according to Claim 15, characterised in that the excitation and signal conditioning circuit comprises first compensators for performing control loop compensation on the respective enor signals associated with the synchronous perturbation component ofthe power amplifier output. 17. An electronic system according to Claim 11 or 12, characterised in that the excitation and signal conditioning circuit comprises a first synchronous demodulator 8 which receives respective signals from the amplifier and also receives a synchronous reference e^ and produces a DC output in proportion to the synchronous component ofthe ofthe AC energising signal in the respective amplifier outputs. 18. An electronic system according to claim 17, characterised in that the excitation and signal conditioning circuit comprises a first summing means for summing the respective outputs ofthe first said synchronous demodulator with a reference potential to form an error signal. 19. An electronic system according to claim 18, characterised in that the excitation and signal conditioning circuit comprises a first compensator (8 3 ) for performing control loop compensation of the respective error signals associated with the synchronous perturbation component ofthe power amplifier output. 20. An electronic system according to claim 19, characterised in that the excitation and signal conditioning circuit comprises a function generator which receives the output of the said compensator and produces a substantially sinusoidal output voltage which is synchronous with the reference signal (βrrf ) and proportional in amplitude to the output of the compensator stage; and which feeds a second summing means (8 7 ) for injecting the energization signal into the amplifier inputs. 21. An electronic system substantially as herein before described with reference to Figures 3 to 8 ofthe accompanying drawings.

Inventors: SIDEY ROGER CHARLES HEY, SIDEY, ROGER, CHARLES, HEY
Applicants: SIDEY ROGER CHARLES HEY, SIDEY, ROGER, CHARLES, HEY
Application year: 1996
Main classification: G05B19
IPC codes: G05B19, H02P25