Pulse Drive Circuit For Coils Of Dental Impact Tools And The Like

Abstract

A drive circuit for dental percussion tools or hammers and the like including a power supply coupled with a timing circuit which provides suitable output pulses of selectable frequency. The output of the timing circuit is connected to a recoil-drive pulse forming circuit which includes one shot multivibrators one of which generates recoil pulses and the other of which generates drive pulses immediately following the recoil pulses. These pulses are amplified and applied to the solenoid of the dental hammer unit to alternately energize coils of the solenoid to cause the armature to reciprocate rapidly and impart repetitive impacts to a tool element. The circuit includes means for enabling adjustment of pulse frequency, pulse width and pulse amplitude.

Description

This invention relates to dental and surgical percussion tools and more particularly to a drive circuit for such tools.

An exemplary percussion tool with which the present drive circuit may be used is disclosed in U.S. Pat. No. 2,588,006 issued to Fred M. Hufnagel. A tool of this nature is of pencil-type form so as to be held between the fingers of a dentist or surgeon, and is arranged to carry various tool tips or tool elements, for example, compactors or dental foil condensers of appropriate shapes for the purpose of condensing gold or silver fillings into tooth cavities, or various chisels for the purpose of chipping bone or breaking teeth in the course of dental surgery, or in other branches of surgery. A tool of this nature typically has a tubular body within which is mounted a pair of solenoid coils, such as coils 2 and 3 illustrated diagrammatically in FIG. 1 hereof. An armature 4 of magnetic material is disposed within the coils in a suitable manner and is caused to reciprocate and strike an anvil 5 as a result of alternate energization of the coils 2 and 3. Impacts of the anvil 5 are imparted to a tool element or tool tip 6, it being appreciated that the body of the unit includes suitable supporting structure for these components.

Although said U.S. Pat. No. 2,588,006 discloses a drive circuit for a percussion tool, it is desirable to provide a compact drive circuit which is flexible in operation, such as one which allows flexibility in the frequency of the impacts provided as well as in the force thereof. Accordingly, it is a principal object of the present invention to provide an improved drive circuit for percussion tools.

It is an additional object of this invention to provide a drive circuit for a small hand held percussion tool, which drive circuit enables selection of percussion frequency and force.

Another object of this invention is to provide an improved drive circuit for a dental impact tool.

These and other objects and features of the present invention will become better understood through a consideration of the following description taken in conjunction with the drawing in which:

FIG. 1 is a circuit diagram of a drive circuit for a percussion tool in accordance with the present invention; and

FIG. 2 is a graph illustrating certain operational characteristics of the circuit of FIG. 1.

Turning now to the drawing, the present drive circuit illustrated in FIG. 1 includes generally a power supply 10, filter and voltage regulator 11, timing circuit 12, recoil and drive pulse forming circuit 13, recoil pulse amplifier and output circuit 14, drive pulse amplifier and output circuit 15, and a dental impact tool 16. The power supply 10 includes a power transformer 20 coupled through an on-off switch 21 and a fuse 22 to a suitable AC voltage supply, such as 115 volts AC. The secondary 23 of the transformer 20 is connected through rectifiers 24-27 to provide DC, such as 18 volts DC, to the filter circuit 11. A suitable pilot light 28 may be provided as indicated. The filter 11 functions in a conventional manner to remove AC and serves to regulate the output thereof at a suitable voltage, such as 12 volts DC across lines 30 and 31. A capacitor 32 functions as an input filter, and a diode 33 serves to isolate the regulated DC voltage from surge voltages. A capacitor 34 is a filter capacitor for the voltage regulating portion of the filter circuit 11, and a resistor 35 serves as a voltage dropping resistor. A zener diode 36 functions as a voltage regulator to maintain the desired voltage across the lines 30 and 31.

The timing circuit 12 includes a timing capacitor 38 which is charged through the combination of an adjustable resistor 39 and a fixed resistor 40. As will be apparent to those skilled in the art, the values of the capacitor 38 and resistances 39 and 40 affect the frequency of operation. The resistance 39 is variable so as to select the desired frequency. A resistance 41 is a current limiting resistor which serves to limit the current through a transistor 42 during the discharge cycle of the timing circuit. The transistor 42 is operated as a switch, and is turned on during the discharge cycle. A transistor 43 is coupled as an emitter follower and used to isolate the timing circuit from the pulse forming circuit 13. Resistors 44 and 45 are bias resistances for the emitter follower.

An integrated circuit, such as an RCA CA3026 as identified by reference numerals 48a-48b is provided in the pulse forming circuit 13 and is connected, along with the associated circuit components, to form two separate one shot multivibrators. The first has an output line 49 which supplies recoil pulses, and the second has an output line 50 which supplies drive pulses. A variable resistance 51 is connected in circuit with the first multivibrator to adjust the recoil pulse width. Similarly, a variable resistance 52 is coupled with the second multivibrator to adjust the drive pulse width. The first multivibrator which includes a circuit 48a is triggered from the timing circuit 12 through the transistor emitter follower 43. The second multivibrator which includes the circuit 48b is triggered from the first multivibrator by means of a coupling capacitor 52. As soon as the timing voltage passes a threshold set by the bias resistances 44 and 45, the first multivibrator is triggered and generates an output pulse on the line 49. At the termination of this pulse, a positive going waveform is developed at the capacitor 52 and is coupled to bias resistances 53 and 54 to trigger the second multivibrator. In this manner, the second pulse immediately follows the first pulse. Transistors 56 and 57 amplify the respective pulses from the multivibrators. Waveform 58 in FIG. 2 illustrates the voltage at the junction 59 between the capacitor 38 and resistor 41 of the timing circuit 12, waveform 60 illustrates the voltage at the collector 61 of the transistor amplifier 56, and waveform 62 illustrates the voltage at the collector 63 of the transistor amplifier 57. The first multivibrator triggers at the peaks 63 of the wave 58.

The outputs of the amplifiers 56 and 57 are coupled by respective resistive dividers 65-66 and 67-68 to the bases of respective transistors 69 and 70. The transistor 69 and a transistor 71, and the transistor 70 and a transistor 72, are Darlington connected output pairs. The current supplied to the output transistors may be varied by respective adjustable potentiometers 74 and 75. The common emitters of transistors 71 and 72 are supplied from a variable resistance 76 which may be adjusted to control the total output current. Thus, the variable resistance 74 or the variable resistance 75 can be set to independently vary the amplitude of either the respective recoil or drive pulses; whereas, the variable resistance 76 controls the amplitude of both of these pulses simultaneously. Diodes 78 and 79 limit the inductive backswing from the solenoid coils 2 and 3 of the percussion tool to prevent damage to the transistors in the circuit. If desired, the movable arms of the potentiometers 74 and 75 may be ganged together to provide for simultaneous pulse amplitude adjustment of both the recoil and drive pulses. Additionally, the pulse width of the pulses may be changed by varying the size of capacitors 81 and 82 in the pulse forming circuit 13.

As noted earlier, the timing circuit 12 in conjunction with the pulse forming circuit 13 generates a repetitive series of two pulses, with one pulse immediately following the other. The frequency of the pulses may be adjusted by the variable resistance 39. The first, or recoil, pulse controls a recoil winding used to pull back the armature 4 of the percussion tool, and the second, or "drive," pulse causes the armature to be pulled forward to supply a blow to the anvil 5. The output circuits 14 and 15 switch and carry the heavy currents required by the tool. The recoil and drive pulse widths are independently adjustable by means of variable resistances 51 and 55, and the recoil and drive pulse currents are adjustable by means of the resistances 74 and 75.

The optimum pulse adjustment is obtained where the recoil and drive pulse times are just sufficient to achieve full movement of the armature of the tool. If the pulse durations are made longer they continue to supply power to the coils after the armature has stopped moving thereby regenerating excessive heat. In many applications, the recoil and drive pulse current adjustments can be set for maximum current, or can be used to limit the maximum power, or alternatively the resistance 76 can be varied in the event impacts are too severe. A typical frequency range is 11/2 to 20 hertz. The output recoil and drive pulses typically are 12 volts, with the current thereof adjustable from 3/4 to 3 amperes. A typical pulse width range of adjustment is approximately 4 milliseconds. However, it is to be understood that other frequencies and frequency ranges, as well as pulse voltage and current amplitude, and duration may be provided without departing from the spirit of the present invention.

The present embodiment of this invention is to be considered in all respects as illustrative and not restrictive the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalence of the claims therefor are intended to be embraced therein.

Claims

What is claimed is:

1. A drive circuit for a percussion tool employing coil means to which pulses are supplied to cause an armature to reciprocate and impact a tool element comprising

power source means,

a timing circuit for providing an output pulse train, said timing circuit being coupled to said power source means and having means for adjusting the frequency of said pulse train independent of the frequency of said power source means,

pulse forming circuit means coupled with said timing circuit for generating a series of pulses in response to the signal train from said timing circuit, said series of pulses comprising repetitively occurring first and second pulses with said second pulses immediately following respective first pulses, said pulse forming circuit means including means for adjusting the width of said first and second pulses, and

output circuit means coupled with the said pulse forming circuit means for applying said series of pulses to said percussion tool, said output circuit means including means for adjusting the amplitude of said first and second pulses.

2. A drive circuit as in claim 1 wherein

said pulse forming circuit means comprises a pair of multivibrators, the first of which is triggered by said pulse train for generating said first pulses of said series of pulses, and the second of which is triggered in response to said first pulses of said series for generating said second pulses of said series.

3. A drive circuit as in claim 1 wherein

said output circuit means includes a pair of amplifiers for respectively receiving said first and second pulses of said series of pulses, and includes means (a) for independently adjusting and (b) for simultaneously adjusting the amplitude of said first and second pulses before said pulses are applied to said percussion tool.

4. A drive circuit for a percussion tool employing coil means to which pulses are supplied to cause an armature to reciprocate and rapidly impart impacts to a tool element comprising

power supply means,

a timing circuit for providing an output signal train, said timing circuit being coupled with said power supply means and having means for adjusting the frequency of said signal train independent of the frequency of said power supply means,

pulse forming circuit means coupled with said timing circuit for generating a series of pulses in response to the signal train from said timing circuit, said series of pulses comprising repetitively occurring first and second pulses with said second pulses following respective first pulses, said pulse forming circuit means including means for selectively adjusting the respective widths of said first and second pulses, and

output circuit means coupled with said pulse forming circuit means for applying said series of pulses to said percussion tool, and said output circuit means including means for adjusting the amplitude of said first and second pulses.

5. A drive circuit for a percussion tool employing coil means to which pulses are supplied to cause an armature to reciprocate and impact a tool element comprising

a timing circuit for providing an output pulse train, said timing circuit having means for adjusting the frequency of said pulse train,

pulse forming circuit means coupled with

said timing circuit for generating a series of pulses in response to said pulse train from said timing circuit, said series of pulses comprising repetitively occurring first and second pulses with said second pulses immediately following respective first pulses, said pulse forming circuit means including first and second multivibrators for respectively providing said first and second pulses of said series of pulses, said first multivibrator being triggered by the pulse train from said timing circuit and the second multivibrator being triggered by said first pulses of the series of pulses generated by said first multivibrator, and

output circuit means coupled with said pulse forming circuit means for applying said series of pulses to said percussion tool, said output circuit means comprising a pair of amplifiers for independently amplifying said respective first and second pulses of said series of pulses, and including means for applying the amplified first and second pulses to respective portions of said coil means of said percussion tool.

6. A drive circuit for a percussion tool employing coil means to which pulses are supplied to cause an armature to reciprocate and rapidly impart impacts to a tool element comprising

a timing circuit for providing an output signal train, said timing circuit having means for adjusting the frequency of said signal train,

pulse forming circuit means coupled with said timing circuit for generating a series of pulses in response to the signal train from said timing circuit, said series of pulses comprising repetitively occurring first and second pulses with said second pulses following respective first pulses, said pulse forming circuit means comprising a pair of multivibrators, the first of which is triggered by said signal train for generating said first pulses of said series of pulses, and the second of which is triggered in response to said first pulses of said series for generating said second pulses of said series, and said pulse forming circuit means including means for adjusting the width of said first and second pulses, and

output circuit means coupled with said pulse forming circuit means for applying said series of pulses to said percussion tool, and said output circuit means including means for adjusting the amplitude of said first and second pulses.

7. A drive circuit as in claim 6 wherein

each of said multivibrators includes means for independently adjusting the pulse width of said first and second pulses of said series of pulses.

8. A drive circuit as in claim 7 wherein

said output circuit means includes a pair of amplifiers for respectively receiving said first and second pulses of said series of pulses, and includes means for independently adjusting the amplitude of said first and second pulses before said pulses are applied to said percussion tool.

9. A drive circuit for a percussion tool employing coil means to which pulses are supplied to cause an armature to reciprocate and rapidly impart impacts to a tool element comprising

a timing circuit for providing an output signal train, said timing circuit having means for adjusting the frequency of said signal train,

pulse forming circuit means coupled with said timing circuit for generating a series of pulses in response to the signal train from said timing circuit, said series of pulses comprising repetitively occurring first and second pulses with said second pulses following respective first pulses, said pulse forming circuit means including first and second multivibrators for respectively providing said first and second pulses of said series of pulses, said first multivibrator being triggered by the signal train from said timing circuit and the second multivibrator being triggered by said first pulses of the series of pulses generated by said first multivibrator, and said pulse forming circuit means including means for adjusting the width of said first and second pulses, and

output circuit means coupled with said pulse forming circuit means for applying said series of pulses to said percussion tool, said output circuit means comprising a pair of amplifiers for independently amplifying said respective first and second pulses of said series of pulses, and said output circuit means including means for adjusting the amplitude of said first and second pulses and means for applying the amplified first and second pulses to respective portions of said coil means of said percussion tool.

10. A drive circuit for a percussion tool employing recoil and drive coils to which recoil and drive impulses are supplied to cause an armature to reciprocate and impact a tool element, comprising

power source means,

timing circuit means for providing an output pulse train, said timing circuit means being coupled to said power source means and having means for adjusting the frequency of said pulse train independent of the frequency of said power source means,

pulse forming circuit means coupled with said timing circuit means for generating a series of pulses in response to said pulse train from said timing circuit means, said pulse forming circuit means including first and second stages with the first of said stages being responsive to said timing circuit means for generating recoil pulses and the second of said stages being responsive to the first of said stages for generating drive pulses, with the drive pulses immediately following respective recoil pulses, said pulse forming circuit means including means for adjusting the pulse width of said recoil and drive pulses, and

output circuit means coupled with said pulse forming circuit means for applying said recoil and drive pulses respectively to the recoil and drive coils of said percussion tool, said output circuit means including amplifier means and means for independently adjusting the amplitude of said recoil pulses and said drive pulses before application thereof to said coils.