US3691437A

US3691437A - Control means for electric tools

Info

Publication number: US3691437A
Application number: US186260A
Authority: US
Inventors: Arne Hilding Andersson; Lennart Axel Duren
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-10-04
Filing date: 1971-10-04
Publication date: 1972-09-12
Anticipated expiration: 1989-09-12

Abstract

A magnetostrictive transducer is vibrated at an ultra-sonic frequency by a driver winding supplied with energizing current from a generator, the output level of which is changed through a signal responsive device. The oscillating magnetic field of the driver winding is disturbed by short-circuiting of a control winding in the field. The disturbance is sensed by detector means to produce a signal fed to the signal responsive device.

Description

United States Patent Andersson et al.

CONTROL MEANS FOR ELECTRIC TOOLS Inventors: Arne Hilding Andersson, 5 Videgaten; Lennart Axel Duren, 23 Fagelgaten, both of Nyashamn, Sweden Filed: Oct. 4, 1971 Appl. No.: 186,260

Related US. Application Data Continuation-impart of Ser. No. 9,703, Feb. 9, 1970, abandoned.

US. Cl. ..3l8/118, 310/26, 310/30 Int. Cl. ..H0lv 9/00 Field of Search ..3l0/8, l, 26, 15, 30, 28, 34, 310/35; 318/118, 116, 114, 122-134, 136;

' 32/DIG. 3, DIG. 4

[451 Sept. 12, 1972 [56] References Cited UNITED STATES PATENTS 1,019,213 3/1912 Adams ..310/l9X 2,686,280 8/ 1954 Strong et al. ..3 18/1 25 3,213,537 10/1965 Balamuth et al ..32/28 3,654,540 4/1972 Honig et a1. ..3 18/1 18 Primary Examiner-D. F. Duggan [5 7] ABSTRACT A magnetostrictive transducer is vibrated at an ultra sonic frequency by a driver winding supplied with energizing current from a generator, the output level of which is changed through a Signal responsive device. The oscillating magnetic field of the driver winding is disturbed by short-circuiting of a control winding in the field. The disturbance is sensed by detector means to produce a signal fed to the signal responsive device.

9 Claims, 5 Drawing Figures CONTROL MEANS FOR ELECTRIC TOOLS This invention relates to a control system for vibratory tools and is a continuation-in-part of prior copending application, Ser. No. 9,703, filed Feb. 9, 1970, now abandoned.

Vibratory tools or instruments such as those used for medical or dental purposes employ a magnetostrictive transducer that is driven by an electromagnetic winding at an ultra-sonic frequency. An oscillating current is supplied to the winding from a power control unit located remote from the tool body or instrument handpiece within which the winding is mounted. Generally, a manually operated control such as a foot pedal is associated with the power control unit through which the operator may exercise control over operation of the tool. Although there are advantages in mounting the manual control on the tool body, this arrangement has not been adopted because of circuit wiring complexities, severe sterility requirements and the resultant increase in the bulkiness of the tool. Further, any power controlling switch arrangement heretofore proposed, could not meet electrical safety requirements if made in accordance with a miniature design for mounting on the tool body.

The placement of a power controlling switch on the tool body is especially desirable for ultra-sonic tools having coolant delivery means mounted on the tool body, as well as to avoid the muscle strains and mobility restrictions on an operator using a foot pedal control.

The foregoing problems are overcome by the present invention by utilizing a tool body mounted switch which controls the power output of the tool by merely short-circuiting a control winding positioned adjacent to the driver winding within its magnetic field. Disturbance of the magnetic field by such short-circuiting of the control winding is sensed to produce a control signal carried by conductors to a power control unit in the same flexible cable through which energizing current is carried to the driver winding. The control signal is operative within the power control unit to change the output level of a generator from-which the energizing current is delivered to the driver winding.

FIG. 1 is a side elevation view, with parts broken away and shown in section, of a typical tool constructed in accordance with the present invention.

FIG. 2 is a simplified, basic circuit diagram of the power control system for the tool shown in FIG. 1.

FIG. 3 is a more detailed electrical circuit diagram corresponding to the system shown in FIG. 2.

FIG. 4 is a circuit diagram showing a modification of the system illustrated in FIG. 2.

FIG. 5 is an electrical circuit diagram of another form of power control system for the tool.

FIG. I shows the invention applied, by way of example, to a dental instrument generally referred by reference numeral 10, having an outer casing 12 adapted to be held in the hand from which a vibrating tool element 14 projects. The tool is driven or vibrated at an ultra-sonic frequency by a magnetostrictive trans'-' ducer element 16 at an adjusted energy level or amplitude. A driver winding 18 is accordingly mounted about the transducer element and an energizing current is supplied to the winding oscillating at a corresponding frequency to establish an oscillating magnetic field driving the transducer element.

In accordance with the present invention, a manually actuated control switch 20 is mounted at any suitable location on the casing 12 of the instrument for changing the output energy level of the tool 14. Toward this end the switch 20 is wired to a control winding 22 positioned within the casing in non-symmetrical relation to a pair of oppositely

wound detector windings

24 and 26 or adjacent to winding 26 in the illustrated embodiment. All of the windings are positioned within the magnetic field generated by the driver winding 18. Electrical energy is supplied to the instrument, and signals conducted therefrom through a flexible electrical conduit 28 adapted to be plugged into or connected to a power control unit, generally referred to by reference numeral 30 in FIG. 2.

As shown in FIG. 2, the

detector windings

24 and 26 are connected in series and positioned adjacent opposite ends of the driver winding 18. The

windings

24 and 26 are oppositely wound and have an equal number of turns so that the voltages induced therein by the oscillating magnetic field will be equal and opposite. Thus, a resultant zero voltage will ordinarily ap pear across the

signal lines

32 and 34 to which the

windings

24 and 26 are connected.

An oscillating voltage on the other hand is continuously applied across the driver winding 18 by the

lines

36 and 38 to establish the oscillating magnetic field causing vibration of the transducer element 16. The control winding 22 is positioned adjacent the winding 26 is inductively coupled thereto by the magnetic field so that when the winding 22 is short-circuited by closing of the control switch 20, the voltage induced in winding 26 will be reduced in relation to the voltage induced in the winding 24. As a result of this unbalance, a differential voltage will appear across the

signal lines

32 and 34. This differential voltage signal is applied to an amplitude adjusting component 40 in the power control unit 30 to change the output energy level of the energizing voltage applied to the driver winding 18 through

lines

36 and 38.

With reference to FIG. 3, an available source of AC. voltage, such as a 220 VAC supply, is connected to'the power unit by

power lines

42 and 44. The power lines are connected to the primary of a voltage step-down transformer 46 in an oscillating voltage generator component 48 of the power unit. The transformer secondary is connected to the input terminals of a full-wave rectifier 50 supplying a rectified, d.c. voltage to

power terminals

52 and 54, filtered by the inductance 56 and capacitor 58. The d.c. voltage at

terminals

52 and 54 is modified by the amplitude control component 40 through

lines

60 and 62 and applied to the oscillator 64 in the generator 48 from which an energizing voltage, at two different levels for example, is fed to the driver winding 18.

In FIG. 3, the oscillator 64 includes a transistor 66 having an emitter to which a negative potential is applied from terminal 54 through one winding of the inductive coupling 68 in the emitter-base circuit of the oscillator which also includes the capacitor 70. An oscillating output is produced at the collector of transistor 66 which is fed through line 38 to the driver winding 18 also connected to the positive potential terminal 52 through line 36. The output level of the oscillator is controlled by the positive bias applied to the base of transistor 66 through line 62 from the amplitude control component 40. Thus, the positive potential terminal 52 is alternatively connected through

voltage reducing resistors

72 and 74 in control component 40, to line 62.

The amplitude control component 40 in the illustrated embodiment of FIG. 3, includes a relay switch 76 connected to line 62 and normally engaged with a contact connected to resistor 72. When displaced to its other operative position by energization of relay coil 78, the relay switch 76 engages a contact connected to resistor 74 to change the bias applied to transistor 66 and the output level of oscillator 64.

The relay coil 78 being connected to the positive voltage terminal 52, is energized when transistor 80 is switched on so as to complete a relay energizing circuit through its collector and emitter connected to the negative voltage terminal 54. The transistor 80 is nor mally non-conducting because of a negative bias applied to its base through resistor 82. A positive forwardbiasing signal voltage applied to the base from signal line 32 through diode 84 charges capacitor 86 to switch on the transistor and hold it in its conductive state. The signal voltage is developed, as aforementioned, by short-circuiting of the control winding 22 to unbalance the zero signal output condition of the

windings

24 and 26 existing when the control winding is open. The heat developed during short-circuiting of the winding 22 may be restricted to safe values by either a known current limiting circuit (not shown) or by a sufficiently weak magnetic coupling relationship between

windings

22 and 18.

FIG. 4 illustrates a modification of the arrangement shown in FIG. 2, whereby the switch 20 is only momentarily closed each time a change in output level is desired so as to avoid excessive heating due to prolonged short-circuiting of the winding 22. Momentary short-circuiting of winding 22 by switch 20, produces a pulse signal in

lines

32 and 34 which is amplified by amplifier 88 and rectified by rectifier 90 before being fed to a self-latching type of switching device 92 such as a thyristor, bistable multivibrator or latching relay. The switching device 92 is operative to supply the amplitude control component 40 with a level changing signal that is removed only when another pulse is produced upon momentary closing of switch 20. The pulse signal fed to switching device 92 is processed by a signal shaping circuit 94 so that it will be of fixed duration independent of the period during whichthe switch 20 is closed. This will prevent undesired switching in the event winding 22 is maintained short-circuited for too long a period.

In the foregoing description of the embodiment illustrated in FIGS. 2 and 3, the output of the instrument is intermittently changed from a high level to a reduced lower level in response to short-circuiting of winding 22 for periods of relatively short duration under control of the operator. This operational mode is suitable for example, in tartar removal where only the high level output is utilized simultaneously with the supply of coolant water through tube 96 as shown in HO. 1. The switch must be held closed during idling periods when the reduced output of the instrument is insufficient to perform any work through tool 14. As an alternative to the foregoing operational mode, the instrument may be activated at a high energy level by the operator only while the instrument is in an idling condition at periodic intervals. FIG. 5 illustrates a modified form of power control unit 30 to effect the latter type of operation.

The driver winding 18 as shown in FIG. 5, is energized by the output of oscillator 64 in the generator 48 which is similar to oscillator 64 of FIG. 3 except that no change in base bias is effected by switching between two voltage reducing resistors. Instead the filter circuit, including inductance 56 and capacitor 58, is directly connected to the oscillator. A capacitor 98 is connected between the output terminal 52 and one end of the secondary of input transformer 46' to slowly charge filter capacitor 58 and thereby initiate operation of the oscillator when a predetermined upper threshold voltage is stored in capacitor 58. As soon as oscillator 64' begins to oscillate, capacitor 58 discharges to stop oscillation when its charge drops below a lower threshold value. This cycle is repeated periodically so that the driver winding 18 is intermittently energized at the lower output level.

In the embodiment shown in FIG. 5, the winding 22' is in the form of a resilient conductive ring made of stainless steel, for example, mounted on the casing of the instrument and having normally opened ends constituting contacts 20'. When the ring is compressed, the contacts 20 close to produce the short-circuit signal which is operative through the control component 40 to close a normally opened relay switch 100 connecting an input terminal of the rectifier 50 to a tap 102 on the secondary of input transformer 46. A rectified output from the rectifier is thereby obtained to operate the oscillator 64 at the higher energy level once oscillation has begun.

It will be apparent from the foregoing description that control over the oscillating current level, energizing a driver winding 18 is effected by selectively controlled short-circuiting of a secondary winding in the oscillating magnetic field generated by the driver winding, producing a control signal in response to disturbance of the magnetic field. The disturbance is sensed in the illustrated embodiment by

windings

24 and 26 connected in series and positioned asymmetrically relative to the control winding to produce a differential voltage signal. This signal is operative on the generator driving the winding 18, to change its output level.

We claim:

1. In combination with a tool having a driven element vibrated by a driver winding connected to an oscillating source of energy the output level of which is varied by amplitude adjusting means, control means for the tool comprising signal sensing means connected to the adjusting means and magnetically coupled to the driver winding, a control winding magnetically coupled to the driver winding, and means for selectively shorting the control winding to produce a signal detected by the signal sensing means causing the adjusting means to change the output level of the oscillating source.

2. The combination of claim 1, wherein said signal sensing means comprises a pair of detector windings magnetically coupled to the driver winding in asymmetrical relation to the control winding, means electrically connecting the detector windings to the adjusting means for canceling voltages induced therein, said induced voltages being unbalanced by short circuiting of the control winding to produce a differential voltage 6. The combination of claim 3, wherein the oscillating source includes an oscillator supplying alternating current to the driver winding at different output levels.

7. The combination of claim 6, wherein the oscillating source further includes means for periodically interrupting the output of the oscillator.

8. The combination of claim 1, wherein the oscillating source includes an oscillator supplying alternating current to the driver winding at different output levels.

9. The combination of claim 8, wherein the oscillating source further includes means for periodically interrupting the output of the oscillator.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3. 6 9l.4 7 Da September 12. 1972 Inventor(s) I It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, insert the following assignment data:

-Assignee: Amlab AB, Nynashamn, Sweden-- Signed and sealed this 3rd day of April 1973. v

(SEAL) Attest:

EDWARD M.PLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents (10-69) USCOMM-DC scam-P69 U.S. GOVERNMENT PRINTING OFFICE: 1959 O365-334 UNITED STATES PATENT UFFICE CERTIFICATE F (30 r RECTEN Patent No. 3, 6 9l,43'7

Dated September 12, 1972 n Arne Hildinq Andersson and Lennart Axel Duren It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading,*insert the following assignment data:

-Assignee: Amlab AB, Nynashamn, Sweden-- Signed and sealed this 3rd ,1 dayof April 1973 v (SEAL) Attest:

EDWARD M.PLETCHER,JR.

ROBERT GOTTSCHALK. Attesting Officer Commissioner of Patents Gem r c-1050 (10-69) USCOMM-DC 6D376-P69 U,S. GOVERNMENT PRINTING OFFICE: I969 -365-334

Claims

2. The combination of claim 1, wherein said signal sensing means comprises a pair of detector windings magnetically coupled to the driver winding in asymmetrical relation to the control winding, means electrically connecting the detector windings to the adjusting means for canceling voltages induced therein, said induced voltages being unbalanced by short circuiting of the control winding to produce a differential voltage signal fed to the adjusting means.

3. The combination of claim 2, wherein the detector windings are electrically connected in series and oppositely wound.

4. The combination of claim 3, wherein the output of the oscillating source is maintained at one level as long as the control winding is short circuited.

5. The combination of claim 3, wherein the output of the oscillating source is switched to one level for a period of fixed duration in response to short circuiting of the winding.

6. The combination of claim 3, wherein the oscillating source includes an oscillator supplying alternating current to the driver winding at different output levels.