Abstract:
An arrangement using sensing coils for obtaining flux rate of change information in a magnetic circuit. The arrangement can be used for vibration attenuation in a magnetic forcer system. Active (electric powered) circuitry is used to implement closed loop control of flux rate. The control loop is &#34;broadband&#34; since a broad range of vibration frequencies are attenuated. The arrangement can be applied to magnetic forcer/suspension systems in which vibrations due to magnetic mechanical/magnetic runouts, system mechanical resonances, or external vibration sources are present. The arrangement is particularly applicable for systems with a large number of varying vibration frequencies.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to commonly assigned co-pending U.S. application Ser. No. (File No. 246-92-009) entitled Active Tuned Magnetic Flux Rate Feedback Sensing Arrangement filed by the present inventors on even date herewith. 
     BACKGROUND OF THE INVENTION 
     This invention relates to an arrangement for obtaining flux rate of change information in a magnetic circuit such as may be used for vibration attenuation in a magnetic forcer system. 
     Passive arrangements for the purpose described include spring/mass systems, mechanical dampers and hybrid viscoelastic devices. Active arrangements may be open or closed loop and may include forcer elements or drive elements such as piezoceramic elements, pneumatic/hydraulic drives, or electromagnetic devices which, when used in conjunction with appropriate sensing elements, can be used to actively accomplish the aforenoted vibration attenuation. 
     In an active open loop configuration, a command matching the vibration to be attenuated as a function of time is applied to the forcer element. This configuration works well when the vibration dynamics can be modeled accurately. Alternatively, an active closed loop arrangement can be employed, whereby the vibration is sensed and the sensed information is used to adjust a command matching the vibration. 
     The present invention is similar to the above described active closed loop arrangement which uses &#34;Hall Effect&#34;  devices to measure magnetic flux within an air gap. These devices are operative so that presence of a magnetic field of a proper orientation induces a small voltage in a semiconductor device. The Hall Effect arrangement uses flux as the sensed parameter for vibration attenuation. The present invention, on the other hand, uses flux rate for this purpose. 
     Accordingly, it is the object of the present invention to use a closed loop or feedback arrangement for sensing flux rate of change in a magnetic circuit. 
     SUMMARY OF THE INVENTION 
     This invention contemplates an active broadband magnetic flux rate feedback sensing arrangement wherein a magnetic circuit includes a sensor element and a forcer or drive element in the form of wound wire coils for providing a magnetic flux path. The sensor output is dictated by a command to the forcer element and is conditioned to provide a flux rate output. 
     A broadband compensator integrator applies proportional plus integral characteristics to the flux rate output. Since the flux rate output is poor at low frequencies, a bias trim loop is required to prevent the broadband compensator integrator from &#34;winding up&#34; i.e. becoming saturated. The bias trim loop effectively restricts the authority of the broadband compensator at low frequencies and forces a command signal to match a feedback signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic representation illustrating a magnetic circuit according to the invention. 
     FIG. 2 is a block diagram illustrating a broadband flux rate feedback sensor configuration according to the invention. 
     FIG. 3 is a circuit diagram more specifically illustrating conditioning electronics shown generally in FIG. 2. 
     FIG. 4 is a block diagram more specifically illustrating a broadband compensator integrator and a bias trim control device shown generally in FIG. 2. 
     FIG. 5 is a block diagram illustrating an arrangement for correcting outputs due to variations in the gap between the stator and rotor in the magnetic circuit of FIG. 1. 
     FIG. 6 is a graphical representation illustrating a high bandwidth constant output current to flux relationship resulting from the implementation of the invention illustrated in FIGS. 1-5. 
     FIG. 7 is a graphical representation illustrating the attenuation of variations in flux rate which are not the result of a flux rate command. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference first to FIG. 1, the orientation of a flux rate sensing coil in relation to a drive or forcer coil in a magnetic circuit is illustrated. Thus, a stator is designated by the numeral 2 and a rotor is designated by the numeral 4. Stator 2 carries a drive coil 6 having legs 8 and 10 and carries a sensor coil 12 having legs 14 and 16. 
     Legs 14 and 16 of sensor coil 12 are disposed close to an air gap 18 between stator 2 and rotor 4. With this arrangement, magnetic flux induced in stator 2 moves from the stator to rotor 4 and then back to the stator with minimal pick-up of stray leakage magnetic flux fields in the magnetic circuit. 
     With reference to FIG. 2, sensor coil legs 14 and 16 are connected to conditioning electronics 20. Conditioning electronics 20 provides a flux rate signal which is applied to a broadband compensator integrator 22. 
     The signal from broadband compensator integrator 22, which is a flux rate feedback signal, is applied to a summing device 24. A command signal I c  provided as will be hereinafter described is applied to summing device 24 and is applied to a bias trim control device 30. 
     Summing device 24 sums the signal from broadband compensator integrator 22 with command signal I c  and provides a summed signal which is applied to a broadband compensator 26 and therefrom to a pulse width modulator (PWM) 28 which is connected to one of the legs such as 8 of drive coil 6 for energizing the drive coil. A transconductance power amplifier which may be of the linear or switching pulse width modulated type may be used in place of pulse width modulator 28 as dictated by a particular application of the invention. 
     The signal from pulse width modulator 28 is fed back to summing means 24 so as to be summed thereby with command signal I c . The signal from broadband compensator integrator 22 is applied to summing means 24. Command signal I c  is applied to bias trim control device 30 which is responsive to the signals applied thereto for controlling broadband compensator integrator 22. A closed loop configuration is thus provided. 
     With the arrangement described, a signal is induced in sensor coil 12 due to the rate of change of magnetic flux and is used in a &#34;broadband&#34; closed loop configuration. The signal at the output of sensor coil 12 is N (the number of sensor coil turns) times the rate of change of flux. This signal is processed by conditioning electronics 20 and broadband compensator integrator 22. The processed signal is then fed back to a drive command loop including summing means 24, broadband compensator 26 and pulse width modulator 28. A bias trim control loop including bias trim control device 30 is used to prevent saturation of broadband compensator integrator 22. 
     The arrangement including conditioning electronics 20 shown generally in FIG. 2 is shown more specifically in FIG. 3 and includes overload protection devices 32 and 34, load resistors 36 and 38, a differential amplifier 40 and a noise filter 42. 
     Overload protection device 32 is connected across leg 14 of sensor coil 12 and overload protection device 34 is connected across leg 16 of the sensor coil. Overload protection devices 32 and 34 may be diodes. Load resistor 36 is connected across overload protection device 32 and load resistor 38 is connected across overload protection device 34. The signal from sensor coil 12 is applied through overload protection devices 32 and 34 and load resistors 36 and 38 to a differential amplifier 40 and therefrom through high frequency noise filter 42 which provides a filtered signal. The filtered signal is applied to broadband compensator integrator 22 as shown in FIG. 2. This arrangement is useful for preventing switching noise from pulse width modulator 28 (FIG. 2) from interfering with the operation of the closed loop configuration heretofore described. 
     Differential amplifier 40 rejects common mode voltages that may be present due to operation of pulse width modulator 28, IR drops, or other non-linear effects. Load resistors 36 and 38 are selected in conjunction with overload protection devices 32 and 34, respectively, to limit peak loads. 
     The arrangement including broadband compensator integrator 22 and bias trim control device 30 shown generally in FIG. 2 is shown more specifically in FIG. 4. Broadband compensator integrator 22 applies proportional plus integral factors to the flux rate signal received thereby from conditioning electronics 20 (FIG. 2). Since the flux rate signal is poor at low frequencies, bias trim control as provided by bias trim control device 30 is required to prevent the broadband compensator integrator from &#34;winding up&#34;, i.e. becoming saturated. Bias trim control device 30 effectively restricts the authority of the broadband compensator integrator at low flux rate signal frequencies. 
     To this extent, broadband compensator integrator 22 receives the flux rate signal from conditioning electronics 20 (FIG. 2) and which flux rate signal is applied to a summing means 33 and to an amplifier 35 having a gain factor K 2 . Bias trim control device 30 receives feedback from pulse width modulator 28 (FIG. 2) and command signal I c , and which feedback and command signal are applied to a summing means 37. The output from summing means 37 is applied to a compensating integrator 39 included in bias trim control device 30. Compensating integrator 39 has a compensating integrating factor K(ts+1/S). 
     The output from compensating integrator 39 is applied to summing means 33 in broadband compensator integrator 22 and is summed thereby with the flux rate signal from conditioning electronics 20. 
     Broadband compensator integrator 22 further includes an amplifier 41 having a gain factor K 1 , an integrator 43 having an integrating factor 1/S, a summing means 44 and an amplifier 46 having a gain factor K 3 . 
     The signal from summing means 33 is applied to amplifier 41 and therefrom to integrator 43. The integrated signal is applied to summing means 44 where it is summed thereby with the signal from amplifier 35. The signal from summing means 44 is applied to amplifier 46 which provides the signal which is applied to summing means 24 (FIG. 2). 
     The flux rate feedback signal from broadband compensator integrator 22, and which signal is applied to summing means 24 as heretofore noted, has some sensitivity due to variations in gap 18 between stator 2 and rotor 4 (FIG. 1). These, in effect, are scale factor variations in the flux rate loop and can be corrected using gap information. This correction is implemented as particularly shown in FIG. 5. 
     To this extent, and with reference to FIG. 5, a central processing unit designated by the numeral 48 provides a signal corresponding to a scaled flux command F sc  and a signal G c  corresponding to the ratio of a sensed change in gap 18 between stator 2 and rotor 4 and a nominal gap, and which output is designated as G c . 
     Signal F sc  is a high bandwidth signal which is applied to a high pass filter 50 and therefrom to a summing means 52 and is applied to a low pass filter 54. Signal G c  is a low bandwidth signal which is applied to low pass filter 54 and provides a scaling factor for the output of low pass filter 54 commensurate with the gap between stator 2 and rotor 4. Summing means 52 sums the signals from filters 50 and 54 and provides a summed signal which is applied to a filter 56 and therefrom to an amplifier 58. The output from amplifier 58 is command signal I c . 
     Thus, low frequency gap (low pass) information is combined with high frequency command input (high pass) information Using a complimentary filter arrangement. 
     The implementation described above results in a high bandwidth constant output flux relationship as particularly shown in FIG. 6 which is a plot of frequency v. gain. However, variations in flux rate that are not the result of a flux rate command are significantly attenuated as particularly shown in FIG. 7 which is a plot of vibration attenuation. In this regard, the broad range of frequency rejection with the described implementation is noted. 
     It will now be appreciated that flux rate feedback using sensing coils as in the present invention provides superior vibration attenuation compared to prior art Hall Effect devices at frequencies greater than zero. In this regard, it will be noted that the voltage obtained from a Hall Effect device is typically small and must be amplified with a high gain device. This makes such an arrangement susceptible to noise which is obviated by the present invention. In further contrast to the prior art Hall Effect devices, said devices are typically limited to a temperature range less than ninety to one hundred and twenty degrees Celsius. Further, the Hall Effect devices require both temperature correction and calibration for non-linear effects and a precision current source is required. The present invention obviates these requirements while providing a flux rate sensor which is relatively simple and does not require calibration. 
     With the above description of the invention in mind, reference is made to the claims appended hereto for a definition of the scope of the invention.