a
`US005736797A
`[11] Patent Number:
`5,736,797
`[45] Date of Patent:
`Apr. 7, 1998
`
`Primary Examiner—Steven L. Stephan
`Assistant Examiner—Judson H. Jones
`Attomey, Agent, or Firm—Burns, Doane, Swecker &
`Mathis, L.L.P.
`ABSTRACT
`[57]
`A linear oscillating motor capable of assuring a consistent
`and effective feedback control of keeping a constant oscil-
`lation amplitude with varying load conditions. The linear
`oscillating motor comprises an oscillator carrying a perma-
`nent magnet, and a stator with an electromagnet. The elec-
`tromagnet is supplied with an electric power to develop an
`electromagnetic drive force of moving the oscillator in a
`linear direction relative to the stator. A spring is provided to
`apply a restoring force to the oscillator for providing a linear
`oscillating motion to the oscillator. A photo-sensor monitors
`the linear motion of the oscillator and outputs a signal to a
`reverse-point detector which determines right and left
`—_Feverse points of the oscillator. A controller applies the
`electric
`power
`to the electromagnet at the drive
`points
`respectively defined subsequentin time to the reverse points
`and in a varying amount for keeping a constantoscillation
`amplitude of the oscillator. The photo-sensor outputs a train
`of pulses appearing each time the oscillator passes its
`oscillation center. The reverse-point detector determines the
`reverse points based upon a time period between the two
`preceding pulses. Since the photo-sensor can monitor an
`0Stillation cycle of the oscillator withoutbeingaffected by
`ihe magne acl developed by me sememagnet for
`ving
`the oscillator, it provides a reliable basis
`for accu-
`ately determining the reverse points and therefore the drive
`points. Accordingly, the driving force can be applied at an
`optimum timing to make the feedback control accurately and
`reliably.
`¥
`
`8 Claims, 6 Drawing Sheets
`
`United States Patent 19
`Motohashiet al.
`
`[54] LINEAR OSCILLATING MOTOR
`
`[75]
`
`Inventors: Ryo Motohashi; Masao Tanahashi;
`Hidetoshi Amaya; Takio Maekawa;
`Toyokatsu Okamoto; Yasuo Ibuki., all
`of Hikone, Japan; Claude Oudet.,
`Besancon; Daniel Prudham,Thise,
`both of France
`.
`,
`.
`[73] Assignee: Matsushita Electric Works, Ltd.,
`Osaka, Japan
`
`[21] Appl. No.: 658,825
`14.
`[22] Filed:
`May 31, 1996
`Priority Data
`30
`Foreign
`Application
`sroray
`&e
`0]
`ten Application
`May 31,1995
`[JP]
`Japan oon.cesessesesscssscerreecores 7-134441
`[51]
`Tint. CLS cecnsnnnntnneninennnnense 02K 33/12
`[52] US. De ener
`~ 310/36; 318/119, 318/128
`
`(58] Field of Search 20.0...secs 310/36; 318/119,
`318/126, 127, 128
`
`[56]
`
`References Cited
`
`4,392,092
`4,583,027
`4,719,698
`5,632,087
`
`U.S. PATENT DOCUMENTS
`7/1983. Gassmer sersevicvssunsseenescreneene 318/127
`4/1986 Parker etal...
`vee 318/128
`
`1/1988 Ninomiyaet al.
`..
`. 30/43.6
`5/1997 Motohashi et al. ............... 30/43.92
`
`FOREIGN PATENT DOCUMENTS
`349077
`3/1990 European Pat. Off.
`.
`2753749
`6/1979. Germany.
`
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`US. Patent
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`Apr. 7, 1998
`
`Sheet 1 of 6
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`5,736,797
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`FIG. 1
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`U.S. Patent
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`Apr. 7, 1998
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`Sheet 2 of 6
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`5,736,797
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`U.S. Patent
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`Apr. 7, 1998
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`Sheet 3 of 6
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`U.S. Patent
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`Apr. 7, 1998
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`5,736,797
`
`1
`LINEAR OSCILLATING MOTOR
`
`BACKGROUNDOF THE INVENTION
`
`1. Field of the Invention
`The present invention is directed to a liner oscillating
`motor, and moreparticularly to such linear oscillating motor
`with a feedback control of maintaining an oscillation ampli-
`tude at constant in a varying load condition.
`2. Description of the Prior Art
`European Patent Publication EP 349077 disclosesa linear
`oscillating motor for use in a dry shaver to reciprocate a
`movable cutter relative to a stationary cutter. The linear
`motor comprises an electromagnetas a stator and a perma-
`nent magnet as an oscillator for driving the movable cutter.
`The electromagnet is energized by a current of a fixed
`frequency to drive the oscillator. When the oscillator or
`movable cutter experiences a heavy load during the shaving,
`the movable cutter moves only by a slight stroke, which
`reduces an oscillation amplitude with an attendant decrease
`in the speed of the movable cutter, thereby reducing cutting
`sharpness and even failing to cut the hairs. Another liner
`oscillating motor is proposed in U.S. patent application No.
`08/413,201 to achieve a feedback control of keeping a
`constant oscillation amplitude with changing load condition.
`The control is contemplated to feed the electric power in a .
`controlled amountat a suitable timing in order to continue
`the oscillation at a minimum power requirement. That is, a
`driving force is required to be applied to the oscillator
`shortly after the oscillator passes the reverse point.
`Therefore, the reverse points shouid be identified to deter-
`mine a drive point of applying the driving force to the
`oscillator. A coil sensor is utilized to monitor the oscillation
`and outputsinusoidal voltage from whichthe reverse points
`are identified as zero-cross points of the voltage. However,
`the coil sensor is likely to suffer from an external magnetic
`field developed around the electromagnet inherent to the
`linear motor and therefore may fail
`to give an accurate
`output truly indicative of the actual oscillation motion, thus
`making it difficult to give accurate reverse points and the
`drive points consistently. With this consequence,the driving
`force may not be applied at a desired timing. Further, it is
`even possible that the drive point is largely offset from a
`desired point by an extent that the driving force is applied to
`move theoscillator in the opposite direction to the direction
`in which the oscillator is moving, leading to uncontrolled
`oscillation.
`
`SUMMARY OF THE INVENTION
`
`The above problem has been eliminated in the present
`invention which providesa linear oscillating motor capable
`of assuring a consistent and effective feedback control of
`keeping a constantoscillation amplitude with varying load
`conditions. The linear oscillating motor in accordance with
`the present invention comprises a linear oscillator movably
`supported to a base frame and carrying a permanent magnet,
`and a stator fixed to the base frame and provided with an
`electromagnet. The electromagnet is supplied with an elec-
`tric power to develop in cooperation with the permanent
`magnet an electromagnetic drive force of moving the oscil-
`lator in a linear direction relative to the stator. A spring is
`provided to apply a restoring force to the oscillator for
`reversing the linear motion, thus providing a linear oscillat-
`ing motion to the oscillator. A sensor is included to monitor
`the linear motion of the oscillator and outputs a signal
`indicative of the linear motion. Also included in cooperation
`with the sensoris areverse-point detector which. based upon
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`the signal from the sensor, determinesright andleft reverse
`points of the oscillator. Further, there is provided a speed
`detector which, based upon the signal from the sensor,
`derives an instantaneous speed of the oscillator. A controller
`applies the electric power to the electromagnet at right and
`left drive points respectively defined subsequent in time to
`the right and left reverse points and in a varying amountfor
`keeping an oscillation amplitude of the oscillator at constant.
`The sensor comprises a photo-sensor which outputsa train
`of pulses appearing each time the oscillator passes its
`oscillation center. The reverse-point detector determines the
`reverse point based upon a time period between the two
`preceding pulses. The photo-sensor can monitor an oscilla-
`tion cycle of the oscillator without being affected by the
`magnetic field developed around the electromagnetfor driv-
`ing the oscillator and provides a basis for accurately deter-
`mining the right and left reverse points and therefore the
`drive points. Accordingly, the driving force can be applied at
`an optimum timing, i.e.. the drive points, which assures an
`accurate and reliable feedback control to give a constant
`oscillation amplitude under varying load conditions.
`Eachofright andleft drive points is defined to precede an
`immediately following point where the oscillator reaches the
`oscillation center. Thus defined drive point is experimentally
`foundto be effective for minimizing the power requirement
`to maintain the oscillation.
`In a preferred embodiment, the reverse-point detector
`defines a right-side oscillation time period between thefirst
`and second of four consecutive pulses and definesa left-side
`oscillation time period between the second andthird of the
`four consecutive pulses. The right-side oscillation time
`period corresponds to one-half cycle of the oscillator where
`the oscillator moves in a right-side region of the oscillation
`center, andthe left-side oscillation time period corresponds
`to a subsequent half cycle of the oscillator where the
`oscillator moves in a left-side region of the oscillation
`center. The reverse-point detector determines the right
`reverse point as delayed from the third pulse by a one-half
`of the above defined right-side oscillation time period and
`determinesthe left reverse point as delayed from the fourth
`pulse by one-half of the above defined left-side oscillation
`time period. Thus, the right and left reverse points can be
`separately determined respectively to well refiect the motion
`in each half cycle, thereby enabling the feedback control
`more consistently with the actual oscillating motion. More
`particularly, even when there is deviation between the true
`oscillation center and the output pulse from the photo-
`sensor, the deviation can be well compensated by the above
`scheme to give reliable right and left reverse points and
`therefore the drive points.
`Alternately, when the output pulse of the photo-sensor can
`be made in exact coincidence with the oscillation center,it
`maybe sufficient to determinethe reverse points in a manner
`as follows. A reference oscillation time period is defined by
`the reverse-point detector as a duration betweenthefirst and
`second of three consecutive pulses and therefore corre-
`spondsto one-half cycle of the oscillator. The reverse-point
`detector determines the right reverse point as delayed from
`the second pulse by a one-half of the reference oscillation
`time period and determinesthe left reverse point as delayed
`from the third pulse by one-half of the reference oscillation
`time period.
`The driving force is applied to the oscillator in each half
`cycle and in the opposite direction to effect the feedback
`control in each half cycle for smooth oscillating movement.
`Thatis, the controller generatesfirst and second drive pulses
`intermittently for feeding the electric power to the electro-
`
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`5,736,797
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`3
`magnet in a direction of alternately changing the moving
`direction of the oscillator. In doing so, the controller gives a
`direction index indicating which oneof the first and second
`drive pulses is to be generated subsequently. An auxiliary
`sensor is included to monitor the oscillatory motion of the
`oscillator and provide an output indicative thereof. Associ-
`ated with the auxiliary sensor is a direction detector which
`detects a moving direction of the oscillator from the output
`of the auxiliary sensor. The controller includes a safe-guard
`circuit which allows to generate the first or second drive
`pulse only after the moving direction detected by the direc-
`tion detector becomes coincident with a direction given by
`the direction index. With this safe-guard circuit, it is made
`to eliminate a possibility that the driving force is applied in
`the opposite direction to the direction in which the oscillator
`is moving. Such contradiction might otherwise occur when
`the oscillator is braked considerably for some reason. Upon
`this occurrence, the actual reverse point of the oscillator is
`delayed from the expected reverse point determined based
`upon the output of the photo-sensor such that the driving
`force would be wrongly applied in the opposite direction
`than intended before the oscillator passes the actual reverse
`point, thereby resulting in uncontrolled oscillation. Even in
`such condition, the safe-guard circuit inhibits the drive force
`from being applied to the oscillator until the oscillator passes
`the actual reverse point, thereby enabling to apply the drive
`force in the correct direction and therefore reliably recover
`the oscillation.
`
`Whenthe oscillator is unintentionally stopped or caused
`to be stopped due to a heavy load. a stopper circuit operates
`to stop the motorfor safety purpose. To this end, the stopper
`circuit starts counting a time duration from the reverse point
`and resets the time duration to zero each time the detected
`moving direction becomes coincident with the direction
`index. When thus counted time duration exceeds a critical
`level, the stopper circuit stops feeding the electric power to
`deenergize the motor.
`The auxiliary sensor may comprises a winding and a
`sensor magnet carried on the oscillator. The winding gen-
`erates a sinusoidal voltage indicative of the changing mov-
`ing direction in response to the movementof the oscillator.
`These andstill other objects and advantageousfeatures of
`the present invention will be apparent from the following
`description of the embodimentofthe present invention when
`taken in conjunction with attached drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic view ofa linear oscillating motorin
`accordance with one embodimentof the present invention;
`FIG. 2 is an exploded perspective view of the linear
`oscillating motor adapted for use in a dry shaver;
`FIG. 3 is an exploded perspective view of oscillators of
`the motor;
`FIG. 4 is a block diagram illustrating a circuit of the
`motor;
`FIG.§ is a chart illustrating a scheme of feedback control
`for the motor; and
`FIG. 6 is a chart illustrating another scheme of the
`feedback control of the motor.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENT
`
`FIG.1 illustrates schematically a basic configuration of a
`linear oscillating motor which comprises a stator 10 and an
`oscillator 30. The stator 10 is mounted to a base frame 11
`
`4
`and comprises an electromagnet 20 with a winding 24
`around a core 22 of a yoke 21 secured to a base frame 11.
`A driver 25 is connected to supply an alternating electric
`current in a controlled amount to the electromagnet 20 in a
`manner as described hereinafter for control of the motor. The
`oscillator 30 is supported by springs 31 to the base frame 11
`to be movablein a linear direction relative to the stator 10
`with a small fixed clearance between a lower end face of the
`oscillator 30 and the upper end of the yoke 21. Carried on
`the oscillator 30 is a permanent magnet 32 which is mag-
`netized to have opposite polarity ends arranged along the
`linear moving direction of the oscillator 30.
`It
`is this
`permanent magnet 32that defines the lower end face of the
`oscillator 30 and is cooperative with the electromagnet 20 to
`receive an electromagnetic drive force for moving the oscil-
`lator 30. The springs 31 are cooperative with a horizontal
`component of magnetic compliance of the motor to provide
`an oscillation system for the oscillator 30 having a natural
`frequency.
`FIGS. 2 and 3 illustrate one example of the motor adapted
`for use in a dry shaver. The electromagnet 20 is fixedly
`suspended from the base frame 11 by engagementof studs
`26 on the yoke 21 with slots 16 at the lower end of the base
`frame 11. The base frame 11 carries a pair of the counter-
`moving oscillator 30A and 30B each provided with joints
`39A and 39B for reciprocating an inner cutter (not shown)
`in sheafing engagement with an outer cutter (not shown)to
`make shaving. Theoscillators 30A and 30B are suspended to
`the base frame 11 respectively by leaf springs 31A and 31B
`to be separately movablerelative to the electromagnet 20.
`Theleaf springs 31A and 31B are securedat their upper ends
`to the opposite upper ends of the base frame 11 andat their
`lower ends to the opposite lower endsof the oscillators 360A
`and 30B so that the oscillator 30A and 30B are movable
`between opposite side walls 12 of the base frame 11. The
`oscillators 30A and 30B are each provided with the perma-
`nent magnet 32A and 32B which are opposed to the upper
`pole end face of the electromagnet 20. As shownin FIG.3,
`the oscillators 30A and 30B comprise plastic-made carrier
`33A and 33B respectively having integrally molded-in metal
`skeletons 34A and 34B which givesrigidity to the oscillators
`and are formed respectively with connections 35A and 35B
`to the leaf springs 31A and 31B. The one carrier 33A is in
`the form of a rectangular open frame into which the other
`carrier 33B is disposed with coil springs 36 interposed
`betweena center post 37 of the carrier 33B and opposed end
`walls of the rectangular carrier 33A. The coil springs 36 are
`cooperative with the corresponding leaf spring 31A and 31B
`to give restoring forces which counteract the magnetic
`driving force intermittently developed by the electromagnet
`20 for establishing the oscillation system. The carriers 33A
`and 33B are interlocked by means of a link 38 pivotally
`supported to the base frame 11 so that the oscillators 30A
`and 30B oscillate synchronously in counter directions.
`Now, discussion is made to a feedback control which is
`included in the motor to keep a constantoscillation ampli-
`tude of the oscillator 30 against possible varying load
`conditions. The oscillation of the oscillator is constantly
`monitored by combination of a photo-sensor 40 and a coil
`sensor 50. The photo-sensor 40 is held on the base frame 11
`and is cooperative with a sensor plate 42 fixed to the carrier
`33A, ie., the oscillator 30A to output a signal indicating
`oscillation center and speed of the oscillator. The sensor
`plate 42 has a slit 43 and is located in a groove 41 of the
`photo-sensor 40 so that, each timethe slit 48 traverses a light
`path in the groove, the photo-sensor 40 respondsto issue a
`pulse. The photo-sensor 40 is arranged to outputthe pulse
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`each timethe slit 48, i.e., the oscillator 30 passes acrossits
`oscillation center. Consequently, it is capable of detecting
`the oscillation center of the oscillator 30 from timing at
`which the pulse is output and also of detecting speed of the
`oscillator from the width of the pulse. The coil sensor 50
`comprises a sensor winding 51 which is fitted in an opening
`17 of the base frame 11 on opposite of the photo-sensor 40
`and is cooperative with a sensor magnet 52 embedded in the
`center of the oscillator 30A to give a sinusoidal voltage
`signal as the oscillator 30 oscillates. The output voltage from
`the coil sensor 50 is therefore indicative of an instantaneous
`direction in which the oscillator 30 is moving. A Hall effect
`device may beutilized instead of the sensor winding to give
`the same sinusoidal output.
`The details of the feedback control is now discussed with
`reference to FIGS. 4 and 5. A controller 6@ is provided to
`effect the feedback control based upon the outputs from the
`photo-sensor 40 and the coil sensor 50 for varying a time of
`supplying the electric current from a power source 61to the
`electromagnet 20 through an inverter 63 in order to keep a
`constant oscillation amplitude. The controller 60 is con-
`nected to a pulse width modulator (PWM) 62 and the
`inverter 63 to vary a pulse-width of a drive pulse for feeding
`the electric current and to alternate the direction of the
`electric current being fed to the electromagnet 20. The
`feedback control becomesoperative in a short time after the
`motor is started. At the start of the motor, the controller 60
`allows to generate a few initial drive pulses of a fixed width
`at a fixed timing calculated in view of the natural frequency
`of the oscillator 30, until the oscillator 30 reaches a stable
`oscillation where a predetermined oscillation amplitude is
`accomplished. Thereafter, the controller 60 becomes respon-
`sible for determining a correct drive point of supplying the
`electric current in each half cycle of the oscillation as well
`as for varying the time of supplying the electric current, i.c.,
`the pulse width of the drive pulse to keep the constant
`oscillation amplitude. Through simulationtests, it is found
`that the drive points of applying the electric current are
`preferred to be immediately after the oscillator passes
`through its right and left reverse points. The drive points can
`be therefore defined to delay from the right andleft reverse
`points PR and PL by a fixed short time period TX. The
`reverse points are determined based upon the output from
`the photo-sensor 40.
`During the stable oscillation, the photo-sensor 40 outputs
`a train of the pulses which, as shown in FIG. 5, appear at the
`timing where the oscillator 30 passes across the oscillation
`center with a pulse width corresponding to an instantaneous
`speedofthe oscillator 30. The output of the photo-sensor 40
`is fed to a reverse-point detector 45 which expects a next
`reverse point from the preceding pulses detected. In order to
`determine the next right reverse point PR, three preceding
`pulses (1) to (3) are taken into the detector 45 to give a
`right-side oscillation time TR period between the first and
`second of the three preceding pulses. The right-side oscil-
`lation time period TR is meant to denote one-half cycle of
`the oscillator where the oscillator 30 moves in a right-side
`region of the oscillation center. Then, the right reverse point
`PR is determined to delay from the third pulse @) by
`one-half ofthe right-side oscillation time period TR/2.In the
`like manner,the next left reverse point PL is determined at
`the detector 45 by taking three preceding pulses (2) to (4) to
`give a left-side oscillation time period TL between the
`second andthird of the three preceding pulses as indicative
`of the subsequent half cycle of the oscillator where the
`oscillator moves in a left-side region of the oscillation
`center. Then,the left reverse point PL is determined to delay
`
`6
`from the third pulse (4) by one-half of the left-side oscilla-
`tion time period TL/2. Based upon thus obtaining right and
`left points PR and PL, the controller 60 determines subse-
`quent driving points DP of applying the drive pulse as
`delayed therefrom by the fixed time Tx.
`the output of the
`Also during the stable oscillation,
`photo-sensor 42 is fed to a speed detector 46 which detects
`the instantaneous speed of the oscillator 30 moving across
`the oscillation center as a function of the width TS of the
`pulse from the photo-sensor 42. The detected speed is taken
`into the controller 60 which in tum varies the width of the
`drive pulse of feeding the electric currentto the electromag-
`net 20 in a feedback manner so as to keep the constant
`oscillation amplitude. For consistent feedback control of
`varying the electric power in correspondence to the moving
`direction of the oscillator 30,
`the compensation of the
`amount ofthe electric current for the osciliator moving in a
`given direction is based upon the detected speed of the
`oscillator moving in the same direction. That is, when the
`oscillator 30 is moving left, the feedback control is based
`upon the detected speed of the oscillator moving from right
`to left and vice versa.
`With the provision of the above scheme of determining
`the right andleft reverse points individually based upon the
`right-side oscillation time period TR and the light-side
`oscillation time period TL, the reverse points can be accu-
`rately determined even whenthe output pulse of the photo-
`sensor 40 is not exactly coincidence with the oscillation
`center of the oscillator, for example, where the slit 43 of the
`sensor plate 42 at the oscillation center is out of center, or
`deviated from the light path of the photo-sensor 40 to
`thereby cause the photo-sensor to output the pulse at the
`timing offset from the oscillation center.
`The controller 60 is arranged to generate the drive pulses
`in order to alternately change the polarity of the electric
`current being fed to the electromagnet 20. That is,
`the
`controller 90 outputs first (right) and second (left) drive
`pulses respectively for moving the oscillator 30 right and
`left. However, a safe-guard is preferred to be included in the
`controller 60 to check the instantaneous moving direction of
`the oscillator for generating the correct drive pulse for
`adding the drive force to the oscillator 30 in the same
`direction in which the oscillator is moving. This is particu-
`larly advantageous to keep the oscillation even when an
`external force is applied to impede the oscillation in such a
`manner as to prolong the oscillation cycle unduly beyond an
`expected variation. When such abnormal condition is met, a
`control would otherwise cause the driving force to be
`applied in the opposite direction than intended, thereby
`failing to keep the oscillation. In order to avoid the problem
`and to give a consistent recovery of the oscillation, a
`safe-guard circuit 70 is preferred to be included in the
`controller 60 to verifies the direction in which the next drive
`force is applied to move the oscillator 30 and the actual
`moving direction of the oscillator 30. A direction detector 55
`is provided to give the actual moving direction of the
`oscillator 30 from the sinusoidal output voltage of the coil
`sensor 50. The controller 60 generates a direction index
`indicating which one of the first (right) and second (left)
`drive pulses is to be issued for the subsequent addition of the
`driving force. The safe-guard circuit 70 allows the controler
`60 to generate the first (right) or second (left) drive pulse
`only after the detected moving direction by the direction
`detector 55 becomescoincident with the direction given by
`the direction index.
`Operation of the safe-guard circuit 70 is explained with
`reference to the right-hand side of FIG. 5. When a heavy
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`5,736,797
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`7
`load is applied at a point H in a direction of prolonging the
`oscillation cycle, the voltage output from the coil sensor 50
`is correspondingly modulated to have an prolonged cycle.
`Even in this abnormal condition, the controller 60 would
`respond to generate the right drive pulse at an expected drive
`point DP’ where the oscillator 30 is normally expected to
`have changed its direction from left to right as indicated a by
`dotted line but where the oscillator 30 is actually still
`moving left as indicated by a solid line. At this moment.
`however,the safe-guard circuit 70 verifies the actual moving
`direction, i.e., left with the direction index, i.e. right, and
`inhibits the controller 60 from giving the right drive pulse
`until the direction detector 55 issues the output indicating
`that the actual movingdirection is changed from left to right.
`Forreliably determining the change of direction from the
`output of the coil sensor 50, the detector is arranged to
`acknowledge the change of direction short time TO after a
`zero-crossing of the output voltage of the coil sensor 50. In
`this manner, the driving force can be applied at a correct
`timing to recover the oscillation even when the oscillator
`suffers from the heavy load.
`Further, the controller may includes a stopper circuit 71
`which stops feeding electric power whenthe oscillator 30 is
`caused to stall substantially under a heavy load, i.c., when
`the drive pulse is not generated over a predeterminedcritical
`time period from the last expected reverse point PR’ or PL’.
`That is, the direction change of the oscillator 30 is not.
`available from the output of the coil sensor 50 over the
`predetermined time period from the expected reverse point
`PR’ or PL’. The stopper circuit 71 starts counting a time
`duration TS from the expected reverse point PR' or PL' and
`resets it to zero each time the detected moving direction
`becomes coincident with the direction index. When thus
`counted time duration TD exceeds the critical time period,
`the stopper circuit 71 causes the controller 60 to stop feeding
`the electric current to the electromagnet 20, thereby stop
`operating the motor.
`In the above embodiment,theright andleft reverse points
`PR and PL are defined respectively from the preceding
`right-side oscillation time period TR and from theleft-side
`oscillation time period TL in order to compensate for
`deviation between the output pulse from the photo-sensor
`and the actual oscillation center of the oscillator 30.
`However,in case where the photo-sensor 4@ can be correctly
`centered with the slit 43 of the sensor plate 42 on the
`oscillator 3, the right and left reverse points can be simply
`determined by the preceding two output pulses from the
`photo-sensor, as shown in FIG. 6. That is, the preceding
`pulses are taken to give a common oscillation time period
`TC so that the next reverse point PR and PL is determined
`to delay from the last pulse by one-half of the time period
`TC/2.In this instance. the instantaneous speed detected as a
`function of the pulse width TS is utilized to vary the time of
`subsequently applying the electric currentto the electromag-
`net for keeping the constant oscillation amplitude.
`In the above embodiment, the feedback amountis calcu-
`lated from the detected speed of the oscillator 30. However,
`it is equally possible to utilize an acceleration of the oscil-
`lator for the same feedback purpose. In this sense, the term
`“speed” utilized throughout the description and claims
`should be understood to encompass the meaning of “accel-
`eration”. Further, the electromagnet and the permanent mag-
`net may be given to the oscillator and the stator without
`departing the scope of the invention.
`Whatis claimed is:
`1. A linear oscillating motor comprising:
`a linear oscillator movably supported to a base frame and
`carrying a permanent magnet;
`
`5
`
`10
`
`15
`
`25
`
`30
`
`8
`stator fixed to said base frame and provided with an
`electromagnet,said electromagnetreceiving an electric
`power to develop in cooperation with the permanent
`magnetan electromagnetic drive force of moving said
`oscillator in a linear direction relative to said stator;
`spring means which applies a restoring force to said
`oscillator for reversing the linear motion, thereby pro-
`viding a linear oscillating motion to said oscillator;
`sensor meansfor sensing the linear motion of the oscil-
`lator to provide a signal indicative thereof,
`a reverse-point detector which, based upon the signal
`from said sensor means, determines right and left
`reverse points of said oscillator;
`a speed detector which, based upon the signal from said
`sensor means, derives an instantaneous speed of said
`oscillator;
`a controller which applies the electric power to said
`electromagnetat right and left drive points respectively
`defined subsequentin time to said right and left reverse
`points and in an a varying amount for keeping an
`oscillation amplitude of the oscillator at constant,
`wherein said sensor means comprises:
`a photo-sensor which outputs a train of pulses appearing
`each time said oscillator passes its oscillation center,
`and wherein
`said reverse-point detector determines said reverse point
`based upon a time period between two preceding
`pulses.
`2. The linear oscillating motor as set forth in claim 1,
`wherein each of said right and left drive point is defined to
`precede immediately following point where said oscillator
`reaches a center of the oscillation.
`3. The linear oscillating motor as set forth in claim 1,
`wherein
`said reverse-point detector defines a right-side oscillation
`time period between the first and second of four con-
`secutive pulses and defines a left-side oscillation time
`period between the second and third of said four
`consecutive pulses, said right-side oscillation time
`period correspondingto one-half cycle of the oscillator
`wheresaid oscillator moves in aright-side region of the
`oscillation center, said left-side oscillation time period
`corresponding to a subsequent half cycle of the oscil-
`lator where said oscillator movesin a left-side region of
`the oscillation center; and wherein
`said reverse-point detector determines said right reverse
`point as delayed from said third pulse by a one-half of
`said right-side oscillation time period and determines
`said left re