POWER AMPLIFIER MODULE FOR A SHAKER

Abstract: A solid state power amplifier module (10) to power a shaker. The module is comprised of a full-wave bridge switching circuit (40) (41) and a filter circuit (42). An input signal from an external source gates the switching circuits, wherein a DC voltage source is switched to the output of the amplifier in accordance with the gating control. The switches (43-46) are comprised of a plurality of parallel MOSFETs. The output of the switching circuits are processed by an L-C filter circuit (55-57) (62). The module is designed to allow a plurality of these modules to be connected in parallel for additional current capability. Inherent in this module design is an out-of saturation detection for current limiting detection.

Description: POWER AMPLIFIER MODULE FOR A SHAKER TECHNICAL FIELD The present invention relates to the field of electronic power amplifiers, and more, specifically to power amplifiers for driving a shaker. BACKGROUND ART There are a considerable number of "shakers" that are well-known in the prior art. These shakers are used to mechanically shake an item for the purpose of diagnostically testing responses to certain driving forces. The item is physically attached to a moving portion of the shaker and when the shaker is activated, the item is subjected to a variety of test conditions. The moving portion of the shaker is typically driven by a force which may be continuous, cyclical or impulsed. One class of these shakers employ the use of an electromagnetic field between field and armature windings. Various driving signals are impressed across the armature winding to control the movement of the shaker. A variety of sensing devices are also employed to provide feedback to the main control unit. To drive this type of a shaker, a power supply is needed to provide electrical power to the field and armature windings. Typically the voltage on one winding (the field winding) is kept constant while the other winding (the armature winding) is driven by a varying signal which then varies the electro-magnetic field for moving the shaker. In the prior art, shaker power supplies were custom designed for a particular shaker, or in many instances, the nearest acceptable unit meeting the shaker ~~2, requirement was configured for use. Further, many prior art shaker power supplies did not provide the precise electronic controls for closely monitoring and controlling the electrical drive of the shaker. As will be disclosed, the present invention provides a shaker power source which is readily adaptable to meet most armature type shaker power requirements, and also provide precise control over the electrical drive of the shaker. DISCLOSURE OF INVENTION A soiid state power amplifier for a shaker is described. A plurality of power modules are coupled to a power source and to an armature winding of an electrically driven shaker. The power modules function as a switching device by modulating a DC input from the power source and generating a modulated drive signal to the shaker. The power modules are comprised of a plurality of individual modules which may be inserted or removed depending on the maximum power requirements of the shaker. Each of these pluggable power modules includes a plurality of MOSFΞT (Metal-Oxide Semiconductor Field Effect Transistor) switches operating as a full-wave bridge. Each of these pluggable power modules includes a plurality of MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) switches operating as a full-wave bridge. A modulator receives feedback signals from the shaker and the power modules. The modulator then provides the necessary control signals to the power modules to properly modulate the drive to the shaker. The modulator is comprised of an oscillator, drive power supply, triangle generator, feedback-error network, comparators and modulator drivers. The oscillator provides the basis for a 56 Kilohertz driving signal which powers the drive power supply and the triangle generator. The comparators compare the feedback signals, which are inputted to the feedback-error network, to the modulated signal of the triangle generator. The output of the comparators are inputted to the modulator drivers which drive the power modules. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a block diagram showing an application of the present invention as a power source for a shaker. Figure 2 is a more detailed block diagram showing power supplies, power modules and a logic module of Figure 1. Figure 3 is a schematic diagram of a power module. Figure 4 is a schematic diagram of a half-wave bridge circuit of Figure 3. Figure 5 is a schematic diagram of a modulator. BEST MODE FOR CARRYING OUT THE INVENTION A solid state power amplifier for a shaker is described. In the following description numerous specific details are set forth such as specific electronic components, switches, signal and control lines, power sources, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practised without these specific details. In other instances, well-known circuits and -4- devices are shown in minimal representation in order not to unnecessarily obscure the present invention. Referring to Figure 1, a power amplifier 10 is shown residing within an equipment cabinet 11. A shaker 12 and its housing 13 is shown removed some distance from the amplifier 10. In most applications, shaker 12 is located within an enclosed area for the purpose of protecting amplifier 10 and operating personnel from an item under test, although such requirement is optional. Shaker 12 contains an armature winding 14 and a field winding 15. Shaker 12, including the two windings 14 and 15, may be any of a variety of prior art shakers that are electrically driven. Amplifier 10 is comprised of a power supply section 16, power module section 17, logic module section 18 and an instrumentation section 19. Power supply section 16 directly provides power to field windings 15 on lines 21 and indirectly provides power -to armature windings 14 on lines 22. A three phase line input on lines 24 to power supply section 16 provides the input power to the amplifier 10. Power module section 17 operates as a switching device by modulating the armature power from power supply section 16 onto armature lines 22. Switching controls of power modules section 17 are directed by control signals from a logic module section 18. Logic module section 18 is coupled to shaker measurement device 25 on line 26 and to various external sensing devices located external to cabinet 11 by line 27. Also, any adjustment devices, such as potentiometers, for setting various control levels are located on logic module section 18. In the preferred embodiment, an accelerometer 28 is used to measure the movement of shaker 12, however, any number or type of prior art devices may be used for such device 25. Line 27 is shown as a single line carrying external sensing signals from shaker 12 and housing 13, but it will be appreciated that any number of lines can readily be used. Sensing signals emanate from devices (not shown) such as interlocks, blower switches, over voltage sensors, etc., which provide monitoring of the environment. Instrumentation section 19 houses testing instruments which may be used for a variety.of purposes well known in the prior art. It will be noted that instrumentation section 19 is not necessarily for practicing the present invention, and is provided strictly for reference in regards to the cabinet 11 layout of the preferred embodiment. Although the preferred embodiment is shown to have a particular configuration within unitary cabinet 11, the configuration is arbitrary and multiple cabinets may -be used as well. Also, like reference numerals are used on the different drawings in which like reference numerals refer to the same parts throughout the several views. Referring to Figure 2, a block diagram of amplifier 10 is shown with pertinent control and power lines. Three phase input lines 24 are coupled to power supply section 16 which is comprised of a DC supply 33 and DC field supply 34. Field supply 34 provides field power directly onto lines 21. DC power supply 33 indirectly provides the drive for armature power on line 22 by providing power to section 17. Although the type and value of the supplies 33 and 34 depend on the shaker, the preferred embodiment sources 170 volts DC unregulated for supply 33 and 440 volts DC for field supply 34. Power module section 17 is further divided into individual . power modules 35. Each power module 35 accepts DC power from supply 33 as V+in and V-in on lines 36. Each power module 35 provides a switching function by modulating the voltage on lines 36 at a modulating frequency determined by a control signal from logic module 18. The modulated output, V+out and V-out from each module 35 is coupled in parallel to provide armature power on line 22. Each power module 35 is a separate self-contained unit which may be inserted or deleted as required by the power requirements of a specific shaker and its configuration. Each power module 35 is designed with a plug capability which allows each module 35 to be placed in parallel, as shown in the drawing Figure 2. The preferred embodiment utilizes up to five power modules 36-40 in parallel such that each module 45 is capable of providing a peak current of 100 amperes for a total current capability of 500 peak amperes when all power modules 36-40 are used. Although the preferred embodiment is shown to use from 1-5 power modules 35, more may be added in parallel without deviating from the spirit and scope of the invention. Logic module section 18 includes a modulator 37 which receives measurement and sensing signals on lines 26 and 27, as well as sensing signals from the power modules 36 through 40 on line 38. Modulator 37 generates control signals on line 39 which provides the pulse width modulation for switching the voltage in power modules 36 through 40. For simplicity, other power and control lines well-known in the prior art which are needed for proper operation of the amplifier 10 are not shown. Power -7-. modules 36-40 are operated in a class D mode utilizing a principle of pulse-width modulation to amplify power. Further, although Figure 1 illustrates the present invention driving an electromagnetically driven shaker, the present invention also operates to drive electro-pneumatic transducers which produce accoustically induced vibrations. The present invention provides the necessary electrical drive for electrically driven shake apparatus. POWER MODULE •A power module 35 of Figure 2 is shown in Figure 3 in more detail. Each module 35 is a high-frequency pulse-width modulated power converter comprising of two half-wave bridge circuits 40 and 41 and a filter circuit 42. Switches 43 and 44 (SI and S2) of circuit 40 and switches 45 and 46 (S3 and S4) of circuit 41 are configured as a full-wave switch. Filter circuit 42 provides the filtering of the output of the switches 43-46. Switches 43-46, are used in the preferred embodiment, are power MOSFETs (Metal-Oxide Semiconductor Field Effect Transistor), although other devices may be readily used. Drains 47 and 48 of switches 43 and 45 are coupled to V+in, while the sources 53 and 54 of switches 44 and 46 are coupled to V-in. A drain 49 of switch 44 and source 51 of switch 43 are coupled to a first side of inductor 55 (LI). A drain 50 of switch 46 and source 52 of switch 45 are coupled to a first side of inductor 57 (L2). A second side of inductor 55 is coupled to a first side of inductor 56 (L3), and also to a first side of capacitor 62 (Cl) . A second side of inductor 56 is coupled to V+out. Similarly, a second side of inductor 57 is coupled to a -8- first side of inductor 58 (L4) and to a second side of capacitor 62. A second side of inductor 58 is coupled to a first side of inductor 63 (L5). A second side of inductor 63 is coupled to V-out. Further, capacitor 61 (C4) is placed between V+out and V-out, capacitor 59 (C2) is placed between V+out and V-in, and capacitor 60 (C3) is placed between the first side of inductor 63 and V-in. The clocking of switches 43-46 is determined by control signals on line 39. Functionally, switches 43 and 46 (SI and S4) are activated together during one time period (as shown by Tl) and switches 44 and 45 (S2 and S3) are activated together during a second time period (as shown by T2). The control signals on line 39 provide gating control and determine the duty cycle times of switches 43-46.- By varying the duty cycles Tl and T2 of switches 43 through 46, a variety of modulated V+out and V-out driving voltages are available on line 22. Typically, duty cycle of T2 is the inverse of duty cycle Tl. Further, a variety of sensing signals, such as over-voltage and over-current signals, are generated within circuits 40 and 41 and are sent out on internal sensing line 38. Circuit 42 provides three levels of filtering for filtering unwanted switching frequencies. Inductors 55 and 57 and capacitor 62 remove the bulk of the noise energy using a differential mode filtering. The common mode energy is transferred back into the power supply via common mode inductors 56 and 58 and capacitors 59 and 60. Any remaining noise is removed by a second stage differential filter comprised of inductor 63 and capacitor 61. Figure 4 is a detailed schematic diagram of the half-wave bridge circuit 40 of Figure 3. The same circuit is duplicated in circuit 41. Switch 43 (SI) of Figure 3 is depicted within the upper box formed by the dotted line. Switch 44 (S2) of Figure 3 is depicted within the lower dotted box. Although switch 43 is shown to be a single switch in Figure 3, in actuality, the preferred embodiment uses a plurality of MOSFETs in parallel. The preferred embodiment utilizes five MOSFETs 69a-e, and because each MOSFET circuitry is identical, the description will only be given to one using a general reference label (such as MOSFET 69). A drain 70 is coupled to V+in. Source 71 is coupled to a first side of fuse 74 and an anode side of zener diode 68. A second side of fuse 74 is coupled to " anode of diode 75 and cathode of diode 75 is coupled to Vout. Gate 73 of MOSFET 69 is coupled to cathode of zener diode 68 and a first side of fuse 76. Second side of fuse 76 is coupled to a f rst side of resistor 77 and a second side of resistor 77 is coupled to output of amplifier 78. ' Varistor 72 is coupled between the source 71 and drain 70. In the parallel configuration, the cathodes of diodes 75a-e are coupled together to output of amplifier 78. Components 68, 72, 74, 75, 76 are used to protect each individual MOSFET such that if one MOSFET fails the protection will prevent the failed MOSFET from effectively shorting across the other parallel set of MOSFETs. Diode 68 and varistor 72 protect the MOSFET 69 from voltage transients. This circuitry of switch 44 (S2) is identical to that of switch 43. Switch 44 is comprised of five power MOSFETs circuitry as in switch 43. Because the function of the circuitry is identical, a prefix 1 has been added to the numbering scheme of switch 43, however the operation and function of the circuitry is equivalent to that of switch 43. Therefore, drain 170 of MOSFET 169 corresponds to drain 70 of MOSFET 69. In this instance, cathodes of diode 175a-e are coupled together to V-in and a second side of resistor 177a-e are coupled together to the output of amplifier 81. Drains 70a-e are coupled together to the output of amplifier 81. Drains 70a-e are coupled together to Vout, which is coupled to filter 42 of Figure 3. Externally to switch 43, a diode 79 is placed between V+in and Vout, wherein a cathode side is coupled to V+in and anode side is coupled to Vout. Similarly, a cathode side of diode 179 is coupled to Vout and an anode side is coupled to V-in. Diodes 79 and 179 provide protection of switches 43 and 44, respectively. Modulating signal A is inputted to optical coupler 81 which is then coupled to the input of driver amplifier 78. Modulating signal B- is inputted to optical coupler 82 wherein the output of optical coupler 82 is coupled to input of driver amplifier 80. A 56 Kilohertz square wave " is inputted to the input o-f low voltage power supplies 83 and 84. Low voltage power supply 83 provide the necessary voltages to operate optocoupler 81 and amplifier 78. Low voltage power- supply 84 provides similar voltages to optocoupler 82 and amplifier 80. The low voltage power supplies 83 and 84 of the preferred embodiment is a full-wave rectifier utilizing a ilter and a regulator at the output. Further, current limiters 85 and 86 provide over current protection for switches 43 and 44. Current limiter 85 coupled to drains 70a-e monitor the amount of current through MOSFET 69a-e. When an overcurrent exists in switch 43, it will be manifested as an excessive voltage drop across switch 43. Current limiter 85 then provides a feedback signal to optocoupler 81 wherein optocoupler 81 is inhibited at a repeated rate of 5 Kilohertz as long as the overcurrent condition exists. Current limiter 86 coupled to drains 170 also provide similar overcurrent protection for switch 44. The output of current limiter 86 provides a feedback signal to optocoupler 82 wherein the overcurrent protection provided is equivalent to that of optocoupler 81 and current limiter 85. In the preferred embodiment, current li iters 85 and 86 employ a simple multi-vibrator to switch at a repeated 5 Kilohertz rate when overcurrent condition is sensed, wherein the 5 Kilohertz disables the 56 Kilohertz activation signal. LOGIC MODULE MODULATOR The modulator 37 of logic module section 18 of Figures 1 and 2 is shown as a schematic diagram in Figure 5. An oscillator comprised of crystal 92 and amplifier 91 generates a 3.58 Megahertz signal which is then divided by a factor of 64 by divider 93. The output of divider 93 is a 56 Kilohertz square wave which is then fed to input of amplifiers 94-97. The output of amplifiers 94-97 are each coupled to the bases of transisters 100-103, respectively. The emitters of transisters 100 and 102 are coupled to +Vcc and the emitters of transisters 101 and 103 are coupled to -Vss. The collector of transister 100 and collector of 'transister 101 are coupled together and the collector of transister 102 and 103 are coupled together. The output of the paired collectors of transistors 100-103 provide a 56 Kilohertz output of which one output is coupled to the low voltage power supplies 83 and 84 of Figure 4. Transisters 100-103 provides a square wave power drive of the 56 Kilohertz signal. The output of divider 93 is also coupled to the input of amplifier 104 through adjustment device 99. A capacitor 105 is coupled between the input and output of amplifier 104 to form a precision integrator. Triangle generator 98 converts the 56 Kilohertz signal to a precision triangle signal, the exact shape determined by device 99. Device 99 may be any automatic of manual -12- adjustment device, such as trim potentiometer, for adjusting the pulse width or amplitude of 56 Kilohertz signal. The triangle generator 98 of the preferred embodiment is a constant current source which produces a precision triangle signal. The output of the triangle generator is then coupled to a first input to each of the pulse width modulation comparators 116 and 118. The measurement signal from the accelerometer 28 is impressed across the two ends of potentiometer 112. A common terminal of potentiometer 112 and the wiper arm are coupled as inputs to buffer amplifier 111 wherein in potentiometer 112 controls the gain of the input signal to amplifier 111. The output of buffer amplifier 111 is coupled to a first input of error amplifier 109. A voltage feedback signal from power module sectioa 18 is coupled as input to feedback amplifier 110 and the output of amplifier 110 is coupled to a second input of error amplifier 109. The output of error amplifier 109 is coupled to a first input of clipper 115. Amplifier 110 also provides scaling down of voltage feedback signal for proportionate scaling input to error amplifier 109. The two inputs to error amplifier 109 are summed with sufficient gain to insure a low distortion output wave form* The system output current is sensed by a Hall effect sensor (not shown) in the main frame and transmitted to current sense amplifier 113. This low level current sense signal is inputted to the input of amplifier 113 wherein the low level signal is amplified and inputted to current limiting adjustment potentiometer 114. Potentiometer 114 may be set to a desired threshold level for clamping the error voltage by having the current threshold level inputted as a second input to clipper 115. The output of the clipper 115 is coupled to a second input of comparator 116 and to a second input of comparator 118 through inverter 117. The error voltage is compared against the triangle by comparators 116 and 118 which creates the pulse-width modulated drive for power modules 37. Modulation limiter placed on the drive signal by modulation stop 119 which is coupled to the outputs to the two comparators 116 and 118 provides maximum amplitude limit on the drive signals. The output of modulation stop 119 is coupled to the input of dead time unit 120 which inserts a dead time into the switching to prevent one switch from turning on before its mate has turned off. The output of dead time unit 120 is coupled to the input of module drivers 121 and 122 which provide the necessary drive to generate drive A and drive B as drive signals to opto-couplers 81 and 82 of Figure 4. Hence, drivers 121 and 122 control the switching of all the power modules. Modulation limiter 119 and dead time unit 120 may be of any prior art circuit well-known for such application. Thus, a solid state power amplifier having a plurality of pluggable power modules and a single modulator for controlling these power modules has been described. Although the amplifiers and modulator of the present invention is used to drive a shaker, it is readily apparent that other electrical devices may be driven without departing from the spirit and scope of the present invention.

Claims: -14- CLAIMS 1. A power amplifier having a gating input and a DC power supply input for providing an amplified output of said gating input to a load comprising: 5 a filter network coupled to said load to provide a filtered output of its input; a first switch coupled between a voltage input of said DC power supply and a first -filter input of said filter network; • j^ o a second switch coupled between said first filter input and a return side of said DC power supply; a third switch coupled between said voltage input and a second filter input of said filter network; a fourth switch coupled between said second 15 filte«r .input and said return side; said gating input coupled to said four switches for closing said first and fourth switches and opening said second and third switches during a first period; and opening said first and fourth switches and closing said 20 second and third switches during a second period; whereby power amplification by full-wave switching is achieved. 2. The power amplifier of claim 1, wherein said switches are metal-oxide semiconductor field effect 2 _ transistors (MOSFET) . 3. The power amplifier of claim 2, wherein each of said four switches is comprised of a plurality of MOSFETs arranged in parallel. 4. The power amplifier of claim 3, wherein each of said MOSFETs having a zener diode placed between its gate and its source for protecting each MOSFET from voltage transients. 5. The power amplifier of claim 4, wherein each of said MOSFETs having a varistor placed between its drain and its source for further protecting each MOSFET from voltage transients. 6. The power amplifier of claim 5, wherein each of said MOSFETs having a first fuse serially coupled to its gate and a second fuse serially coupled to its source for further protecting each MOSFET from excessive current. 7. The power amplifier of claim 6, wherein each of said MOSFETs having a second diode serially coupled to its source for further protecting each MOSFET. 8. The power amplifier of claim 7, wherein each of said four switches having a third diode coupled in parallel for further protecting each said switch. 9. The power amplifier of claim 3 or 8, wherein said filter network includes inductor-capacitor (L-C) filters to provide differential mode and common mode filtering. 10. The power amplifier of claim 9, further including a current limiter coupled to said switches to limit each switch current to a maximum predetermined value. -16- 11. A power amplifier having a gating input and a DC power supply input for providing an amplified output of said gating input to a load comprising: a filter network coupled to said load to provide a filtered output of its input; a first metal-oxide ' semiconductor field effect transistor (MOSFET) having its drain coupled to " a voltage input of said DC power supply and its source coupled to a first filter input of said filter network; a second MOSFET having its drain coupled to said first filter input and its source coupled to a return side of said DC power supply; a third MOSFET having its drain coupled to said voltage input and its source coupled to a second filter input of said filter network; a fourth MOSFET having its drain coupled to said second filter input and its source coupled to said return side; said gating input having a first gating drive and a second gating drive; wherein said first gating drive is coupled to gates of said first and fourth MOSFETs, and said second gating drive is coupled to gates of said second and third MOSFETs, such that first and fourth MOSFETs are active during a first period, and second and third MOSFETs are active during a second period; whereby power amplification by full-wave switching is achieved. -17- 12. The power amplifier of claim 11, wherein each of said MOSFETs is comprised of a plurality of MOSFETs arranged in parallel. 13. . The power amplifier of claim 10, wherein each MOSFET is fused separately to allow other paralleled MOSFETs to continue to operate when one of said MOSFETs fails. 14. The power amplifier of claim 13, wherein each of said MOSFETs having a zener diode placed between its gate and its source for protecting each MOSFET from voltage transients. 15. The power amplifier of claim 14, wherein each of said MOSFETs having a varistor placed between its drain and its source for further protecting each MOSFET from voltage transients. 16. The power amplifier of claim 15, wherein each of said MOSFETs having a first fuse serially coupled to its gate and a second fuse serially coupled to its source for further protecting each MOSFET from excessive current. 17. The power amplifier of claim 16, wherein each of said MOSFETs having a second diode serially coupled to its source for further protecting each MOSFET. 18. The power amplifier of claim 17, wherein each of said four switches having a third diode coupled in parallel for further protecting each said switch. 19. The power amplifier of claim 18, wherein said filter network includes inductor-capacitor (L-C) filters to provide differential mode and common mode filtering. 20. The power amplifier of claim 19, further including a current limiter coupled to each parallel set of MOSFETs to limit current of each parallel set to a maximum predetermined value. 21. The power amplifier of claim 20, further including optical couplers to couple said first and second gating drives to gates of said MOSFETs. 22. The power amplifier of claim 21, wherein said power amplifier is housed in a pluggable module such that a plurality of said modules are placed in parallel for increased current capability. 23. The power amplifier of claim 22, for use in driving a vibration testing device.

Inventors: PAULY WAYNE, PAULY, WAYNE
Applicants: MECHANICAL TECH INC, MECHANICAL TECHNOLOGY INCORPORATED
Application year: 1987
Main classification: H03F3
IPC codes: H03F3