Ultrasonic surgical apparatus

An electrical apparatus for driving an ultrasonic piezoelectric crystal transducer in a surgical handpiece for the fragmentation and aspiration of tissue, which apparatus includes an electronic control loop in combination with a voltage source amplifier having an output which is connected to the piezoelectric crystal transducer with a tuning inductor in parallel. A control system for monitoring the control loop and a component for controlling tissue selectivity are also disclosed.

BACKGROUND OF THE INVENTION 
The present invention relates to an electrical apparatus for driving an 
ultrasonic transducer in a surgical handpiece for the fragmentation and 
aspiration of tissue at an operation site on a patient, and to electronic 
control loops in the electrical circuitry of the apparatus. In particular, 
the invention relates to an apparatus for driving an ultrasonic surgical 
device while maintaining the vibration frequency at mechanical resonance 
utilizing a feedback control. The invention is also concerned with means 
for controlling amplitude and with a digital interface for monitoring 
performance and restoring normal operation when the system parameters 
exceed analog control loop boundaries. The invention also provides means 
for controlling the tissue selectivity of the apparatus. 
The use of ultrasonically vibrating surgical devices for fragmenting and 
removing unwanted tissue by aspiration with precision and safety has led 
to the development of valuable surgical procedures. Initially, the 
technique of surgical aspiration was applied to the fragmentation and 
removal of cataract tissue as disclosed, for example, in U.S. Pat. No. 
3,589,363. Later, similar techniques were applied with significant success 
to neurosurgery and other surgery specialties where the application of 
ultrasonic energy through a handheld device for selectivity removing 
tissue on a layer-by-layer basis with precise control was found to be 
feasible. 
Certain devices known in the art characteristically produce continuous 
vibrations having a substantially constant amplitude at a frequency of 
about twenty to about thirty KHz up to about forty to about fifty KHz. 
U.S. Pat. Nos. 4,063,557, 4,223,676 and 4,425,115 disclose a device 
suitable for the removal of soft tissue which is particularly adapted for 
removing highly compliant elastic tissue mixed with blood. Such a device 
is adapted to be continuously operated when the surgeon wishes to fragment 
and remove tissue, and generally is operated by a foot switch. 
A known instrument for the ultrasonic fragmentation of tissue at an 
operation site and aspiration of the tissue particles and fluid away from 
the site is the CUSA model System 200 Ultrasonic Aspirator manufactured 
and sold by Valleylab, Inc. of Stamford, Conn.; see also U.S. Pat. No. 
4,827,911. When the longitudinally vibrating tip in such an aspirator is 
brought into contact with tissue it gently, selectively and precisely 
fragments and removes the tissue. Advantages of this unique surgical 
instrument include little damage to healthy tissue in a tumor removal 
procedure, blood vessels can be skeletonized, healing of tissue is 
promoted, no charring or tearing of margins of surrounding tissue, only 
minimal pulling of healthy tissue is experienced, and excellent tactile 
feedback for selectively controlled tissue fragmentation and removal is 
provided. 
In many surgical procedures where ultrasonic fragmentation instruments are 
employed additional instruments are required for tissue cutting and 
hemostasis at the operation site. For example, hemostasis is needed in 
desiccation techniques for deep coagulation to dry out large volumes of 
tissue and also in fulguration techniques for spray coagulation to dry out 
the surface of tissues. 
The apparatus disclosed in U.S. Pat. Nos. 4,931,047 and 5,015,227 provides 
hemostasis in combination with an ultrasonically vibrating surgical 
fragmentation instrument and aspirator. The apparatus effectively provides 
both a coagulation capability and an enhanced ability to fragment and 
aspirate tissue in a manner which reduces trauma to surrounding tissue. 
U.S. Pat. No. 4,750,488 and its two continuation U.S. Pat. Nos. 4,750,902 
and 4,922,902 disclose a method and apparatus which utilize a combination 
of ultrasonic fragmentation, aspiration and cauterization. 
In an apparatus which fragments tissue by the ultrasonic vibration of a 
tool tip, it is desirable, for optimum efficiency and energy utilization, 
that the transducer which provides the ultrasonic vibration should operate 
at resonant frequency. When the transducer is a piezoelectric crystal the 
frequency at which it vibrates will correspond to the frequency of the 
electrical driving signal which causes the vibration. The operation is 
most efficient when the transducer vibrates at its resonant frequency. 
However, changes in operational parameters, such as, changes in 
temperature, thermal expansion and load impedance, result in deviations in 
the resonant frequency. 
Accordingly, controlled changes in the frequency of the driving signal are 
required to track the resonant frequency. 
The circuit disclosed in U.S. Pat. No. 4,750,488 includes a frequency 
control loop which depends upon a feedback signal obtained by adding two 
signals that are proportional to the voltage and current input to the 
piezoelectric transducer. 
U.S. Pat. No. 4,965,532 discloses a circuit for driving an ultrasonic 
transducer including a frequency control means utilizing a feedback 
control dependent upon first and second phase detection signals. 
It has now been found that an efficient frequency control is obtained with 
the aid of a unique control loop which includes a feedback piezoelectric 
crystal mechanically coupled to the piezoelectric transducer. 
The use of a feedback crystal in a tuned circuit which provides a filtered 
signal to control a driving signal in an ultrasonic system is disclosed in 
U.S. Pat. No. 4,012,647. The system disclosed in this patent is not a 
surgical apparatus and the combination of ultrasonic vibrator, amplifier 
and tuning inductance with feedback from the feedback crystal to the input 
of the amplifier, constitutes an oscillator. In contrast thereto, the 
novel circuit of the present invention incorporates a voltage controlled 
oscillator (VCO) as part of a control loop. The feedback signal from a 
feedback crystal is input to the control loop which then drives the 
amplifier. The advantage of this novel circuit is that it tracks 
mechanical resonance without electrical interaction. 
A problem which frequently arises during the operation of an ultrasonic 
surgical apparatus which includes a feedback control loop is the 
propensity of the control loop to lock into an unwanted adjacent frequency 
rather than the desired resonant frequency. 
The occurrence of this problem depends upon the frequency spectrum of the 
system and the control loop characteristics. If the control loop is 
underdamped the large transient overshoots upon start-up or rapidly 
changing loads move the driving frequency toward the adjacent frequencies. 
The propensity of the control loop to lock into an unwanted adjacent 
frequency increases with the magnitude of control loop overshoot and the 
proximity of said adjacent frequencies. 
Due to performance requirements and manufacturing variances, it is 
difficult to produce a pure analog control system which is not prone to 
said irregularities. Also, a difficulty in the manufacture of ultrasonic 
vibrators is the variation in resonant frequency due to variations in 
materials and manufacturing processes. Such variations in resonant 
frequency result in a greater magnitude of error signal in the operation 
of the control loop. The probability of irregularities increases in direct 
proportion to the magnitude of the error signal. 
It has now been found that such irregularities may be avoided by the use of 
a microprocessor-based system interactively coupled to an analog control 
loop, which system provides a digital interface for monitoring performance 
and restoring normal operation when the system parameters exceed analog 
control loop boundaries. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there is provided an electrical 
apparatus for driving an ultrasonic piezoelectric crystal transducer in a 
surgical handpiece for the fragmentation and aspiration of tissue, which 
apparatus comprises voltage controlled oscillator in series with an 
amplifier and a first electronic control loop connected from a feedback 
piezoelectric crystal through a phase comparator and a loop filter to the 
voltage controlled oscillator, which feedback crystal is mechanically 
coupled to said transducer and provides a feedback signal which is a 
function of the actual frequency of vibration of the transducer and which 
phase comparator compares the phase of the feedback signal and of the 
driving signal and provides a control signal which maintains the driving 
signal at the resonant frequency of the transducer, wherein said amplifier 
is a voltage source amplifier having an output which is connected to the 
piezoelectric crystal transducer with a tuning inductor in parallel. 
Preferably the handpiece incorporates a piezoelectric crystal transducer 
operatively connected to a tool having a distal tip, which transducer, 
upon activation by an electrical driving signal provided by the apparatus 
according to the invention, ultrasonically vibrates said tool tip so that 
the tip is capable of fragmenting tissue at a surgical operation site, and 
aspiration means for removing fragmented tissue from said site. 
The piezoelectric crystal transducer is connected in parallel to a tuning 
inductor to form a network having a resonant frequency corresponding to 
the operational frequency of the transducer and optimizing the coupling of 
the voltage source amplifier to a real load. A piezoelectric crystal is a 
voltage controlled device and, consequently, the advantage of a voltage 
source amplifier in parallel with a tuning inductor is that it provides a 
more direct control of the piezoelectric driven vibrator. Also, in a 
preferred embodiment, a low value resistor is connected in series on the 
output of the voltage source amplifier for added stability. This preferred 
embodiment is a substantial improvement over the conventional use of a 
series tuning inductor, since the response is instant because there is no 
inductive phase lag. 
The invention also provides an apparatus as described above which includes 
a second control loop comprising means for sensing the amplitude of 
vibration of the transducer and providing an amplitude signal, means for 
comparing the amplitude signal with a command signal adjustable by an 
operator and means for maintaining the vibration at a desired operational 
amplitude under varying loads by adjusting the driving signal as required 
to bring the amplitude level into conformity with the command signal 
level. 
Preferably, the second control loop includes a converter which converts the 
RMS AC feedback signal to DC. 
The invention further provides a control system for monitoring one or more 
electronic control loops to detect and respond to error conditions 
occurring during operations controlled by said loop or loops, which system 
comprises a microprocessor coupled to an analog-to-digital converter and a 
multiplexer, wherein the output from each control loop is input to the 
multiplexer, the output from the multiplexer is converted to digital form 
in the converter to provide an input digital signal which is processed in 
the microprocessor to respond with an appropriate algorithm to correct the 
error condition. 
The above described control system is particularly adapted for monitoring a 
frequency control loop such as the above-described first control loop 
included in an apparatus according to the invention, or for monitoring an 
amplitude gain control loop such as the second control loop included in an 
apparatus according to the invention, or, in the most preferred 
embodiment, for monitoring both first and second control loops. This 
preferred embodiment is more particularly described hereinafter with 
reference to FIG. 1 of the accompanying drawings. 
The invention still further provides an apparatus as described above which 
includes means for achieving tissue selectivity in an ultrasonic surgical 
aspirator comprising a limiter connected to the output of the amplitude 
gain control loop whereby the maximum error signal output by the loop may 
be adjusted and limited by an operator. 
Thus, a preferred handpiece comprises a piezoelectric crystal transducer 
which is operatively connected to a tool having a distal tip, which 
transducer, upon activation by an electrical driving signal, 
ultrasonically vibrates the tool tip so that the tip is capable of 
fragmenting tissue at a surgical site, a feedback piezoelectric crystal 
mechanically coupled to the transducer, and aspiration means for removing 
fragmented tissue from the surgical site. Preferably, the transducer and 
feedback crystal are mounted within an electrically insulated housing and 
switching means for selecting and actuating the various operations are 
mounted on the housing so that the handpiece may be hand-operated.

DETAILED DESCRIPTION OF THE INVENTION 
The apparatus illustrated in FIG. 1 of the drawings comprises a voltage 
controlled oscillator (VCO) 1 which drives, through a power amplifier 2, a 
driving piezoelectric crystal 3 with a sinusoidally oscillating voltage. 
This voltage is imparted to the drive crystal at the output of a voltage 
source power amplifier 2, with a parallel inductor 4 and optionally with 
an impedance matching transformer T (FIG. 1A). Also, for stability, a low 
value resistor R is connected to the output of the amplifier (FIG. 1A). 
The frequency of the oscillation at the output of the VCO is determined by 
the voltage imparted to the input of the VCO. The midpoint of the 
oscillator's frequency range should be set at the point where it is 
anticipated that the system will normally be running and the range of the 
frequency should cover the range over which the system will vary in normal 
use. 
The piezoelectric drive crystal 3 responds to the sinusoidally oscillating 
voltage applied to it by the VCO by vibrating at the same frequency and 
causing the entire ultrasonic vibrator assembly to vibrate at such 
frequency. 
The feedback crystal 5, being in the ultrasonic assembly, vibrates with it. 
When stress is applied to a piezoelectric crystal, the crystal responds by 
developing a proportional voltage. This voltage is an indication of how 
the assembly is vibrating. The amount of deflection of the vibrating 
assembly is indicated by the level of voltage across the feedback crystal. 
If the vibrating assembly is vibrating at a given sinusoidal frequency, 
the voltage signal from the feedback crystal will be a sine wave of such 
frequency. The resonant frequency of oscillation of the vibrating assembly 
is the frequency at which the minimum amount of power is required to drive 
it. This frequency is indicated by a 90 degree phase displacement between 
the sine wave of the driving signal and the sine wave of the feedback 
signal. 
The two signals, drive 6 and feedback 7, are imparted to the inputs of a 
phase comparator 8. The output 9 of the phase comparator gives the cosine 
of the phase angle between the drive and feedback sine wave signals. 
If the resonant frequency is the same as the center frequency of the VCO, 
the VCO will drive the drive crystal at its resonant frequency. The phase 
angle fed back to the phase comparator between drive and feedback will be 
90 degrees giving 0 (zero) volts to the VCO, through a loop filter 10 and 
an amplifier 11 which is described hereinafter; and the VCO will continue 
to drive the vibrating assembly at its resonant frequency. 
If the resonance suddenly changes, due to loading, the phase angle between 
the two waves will no longer be 90 degrees. The output of the phase 
comparator will be the cosine of something other than 90 degrees, which 
will no longer be zero. When this is felt by the VCO (the output of the 
phase comparator is fed to the VCO through a gain amplifier 11), the VCO 
will shift its output frequency in proportion to the gain of the amplifier 
multiplied by the signal from the phase comparator and in a sense so as to 
bring the phase angle between the drive and feedback signals back to 90 
degrees. As the phase angle moves back toward 90 degrees the cosine of the 
phase angle moves back toward zero. The system will be in equilibrium when 
the phase angle is as close to 90 degrees as possible with a voltage level 
applied to the VCO sufficient to maintain oscillation at a frequency 
different from its center frequency to correspond to the new resonant 
frequency. The more gain in the amplifier, the less will be the error. 
Further complication exists due to the fact that the vibrating mechanical 
system has an inertia which impedes the rate at which its vibration 
frequency or amplitude may be changed. A sudden load on the tip of the 
vibrator can change its resonance. The phase comparator 8 will respond by 
applying a correcting voltage through the amplifier 11 to the VCO. If the 
gain of the amplifier is excessive, the VCO will attempt to change the 
driving frequency much faster than the vibrating mechanical assembly can 
respond. By the time the vibrating mechanical assembly reaches the proper 
frequency defining resonance, the VCO will have overshot it by some 
amount. The loop then attempts to correct in the opposite direction and 
once again overshoots, and so on. If the system is stable, the overshoot 
decreases on each cycle and eventually settles. If the system is unstable, 
the overshoot does not decrease on each cycle but either stays constant 
and oscillates or else increases on each cycle until the system locks into 
an adjacent frequency or is damaged. 
The loop consisting of the phase comparator 8, its output 9, the gain 
amplifier 11 and the VCO 1 comprises a phase locked loop (PLL) defined 
schematically by dashed lines 12. 
A second control loop 13 is provided for controlling amplitude. This is the 
automatic gain control loop (AGC). The operator sets the amplitude of 
oscillation required for the vibrating tip at the command input 14. The 
sine wave 7 returning from the feedback crystal is converted to a D.C. 
level as a function of its amplitude by the RMS-to-DC converter 15. This 
signal 16 is then fed to a summing node 17, the output 18 of which is the 
error signal between the feedback and the command input 14, which error 
signal is fed to an error amplifier 19. The error amplifier 19 transmits a 
signal at its output in proportion to the difference between the two 
inputs to the summing node 17. A signal 20 controls the amplitude of the 
drive signal which is the output of the power amplifier 2 which drives the 
driving piezoelectric crystal 3. The system is in equilibrium when the 
least amount of difference exists between the two inputs, 14 and 16, but 
enough difference exists to achieve a level at 20 to drive the crystal and 
feedback a signal from the feedback crystal to achieve this minimal 
difference between 14 and 16. Error decreases with gain, but safe gain 
margins must be maintained to avoid instability. 
One feature of ultrasonic aspirators is the selectivity with which specific 
types of tissue may be fragmented and aspirated with little or no effect 
on adjacent tissue of other specific types. In some surgical procedures 
this is a desirable effect, while in others it is desirable to have a less 
selective fragmentation capability. 
It has been found that a greater or lesser tissue selectivity may be 
achieved by varying, through a limiter 21, the maximum amplitude of the 
driving signal applied by the AGC. The limiter 21 is connected to the 
amplitude gain control loop whereby the maximum error signal output by the 
loop may be adjusted and limited by an operator. 
A multiplexer 22 has as its inputs an error signal 23 from the automatic 
gain control loop (AGC), 13, and an error signal 24 from the PLL. The 
output from the multiplexer is fed to an analog-to-digital converter 25, 
the output of which is transmitted to a microprocessor (.mu.P) 26. An 
output signal 27 from the microprocessor is transmitted to a center 
frequency adjusting unit 28, the output of which is fed to the VCO 1. A 
second output signal 29 from the microprocessor is transmitted to a 
switching unit 30 for switching the command input between either zero or a 
low reference point 31 and an operator amplitude set point 32. 
The system in normal operation is given by the algorithm in FIG. 2. The AGC 
lop error signal 20 is polled and the level is checked 33. A difference 34 
greater than a predetermined value (&gt;A) indicates a stall condition A 
stall condition is such that the amplitude of vibration is substantially 
lower than the commanded input 14 so indicating excessive loading, control 
loop lockup on an adjacent unwanted frequency, or some other error 
condition. If a stall condition is not indicated the polling 33, 34 will 
continue and the PLL is allowed to operate normally. If a stall condition 
is indicated, the PLL error is checked 35. An abnormally high PLL error 36 
(&gt;B) indicates a lockup on an unwanted adjacent frequency. 
If the PLL error is not greater 37 than the predetermined value (&gt;B), and 
the stall condition is indicated, the following algorithm is executed: A 
timer 38 in the microprocessor system 26 is set for a maximum allowable 
period of time for correction. 
The interaction of the microprocessor system in this portion of the 
algorithm is an indication 39 to the operator by means of an appropriate 
audible, visual, tactile or other communication means, that excessive 
pressure is being applied to the ultrasonic surgical handpiece. The 
microprocessor will continue to poll 40, 41 for relief of the pressure and 
for an indication of excessive time by means of the timer 42, 43. Upon 
relief of the stall condition, the microprocessor clears the timer 44 and 
then clears means for operator communication 44 and returns to polling 33, 
34. If the stall is not cleared and the check timer 42 indicates that the 
time limit has been exceeded 43 the system will shut down 45 disallowing 
further operation and an error condition will be signaled to the operator 
by the communication means 45. A condition where both loop errors 34, 36 
are simultaneously in excess of the predetermined values is an indication 
that the system has locked into an unwanted adjacent resonance. One way of 
correcting this condition is to relieve all pressure from the ultrasonic 
surgical device 46, set the timer 47, and switch the commanded input for 
the AGC loop to zero 31. 
Vibration is stopped by applying zero volts 31 through switch 30 to the 
command input 14 of the AGC loop. Ample time 48 is allowed for the 
ultrasonic generator to dissipate all stored energy 48. The command input 
is restored through switch 30 to the operator set level 32. Ample time is 
allowed for the ultrasonic generator to achieve steady state vibration 
amplitude level 49. The error levels are rechecked 50, 51, 52, 53 along 
with the timer 54. If error condition persists 51, the timer is checked 
54. The algorithm will repeat continuously until either the error 
conditions are relieved or the timer value is exceeded 55. If the error 
conditions 50, 51, 52, 53 are relieved prior to the timer value 55 being 
exceeded, the timer is cleared 56, and the algorithm 57 (see FIG. 3) 
adjusts the PLL center frequency. The PLL error correcting algorithm is 
executed, the communication means and timer are cleared 56 and the 
ultrasonic generator is returned to normal operation. If the timer value 
is exceeded 55, the ultrasonic generator is disabled 58 and an error 
message is communicated to the operator by means of the above-described 
communication means 58. 
The operation schematically represented by 57 in FIG. 2 may be defined by 
the algorithm illustrated in FIG. 3. The start of the algorithm is a 
polling 59, 60 to determine whether vibration has been activated 61 or not 
62. At the start of vibration, the difference between the operator 
adjusted commanded input for stroke level and the actual stroke level is 
determined by the level of the AGC loop error signal 63. If the signal is 
not zero 64, a loaded vibration condition is indicated causing the 
algorithm to go to normal operation 65. If the signal is zero 66, the PLL 
error signal is checked 67 to determine if zero error exists 67. If zero 
error exists 68, the algorithm goes to normal operation 69. If the error 
is not zero 70, a determination of the direction of the error is made 71, 
72 and an increment of adjustment is imparted to the VCO in the 
appropriate direction, either higher 73 or lower 74. A loop settling time 
is allowed 75 (timeout) and the error is once again checked 67. This is 
repeated until the error is zeroed 68 after which the system is returned 
to normal operation 69. 
The handpiece illustrated in FIGS. 4-7 of the accompanying drawings 
comprises a housing 110, which is preferably made of an electrically 
insulating plastic material. The housing accommodates a piezoelectric 
crystal transducer comprising a stack of toroidal piezoelectric crystals 
111. Each crystal is mechanically coupled to each adjacent crystal and 
each crystal is energized with alternating electrical energy by opposite 
polarity electrodes on either side of each crystal. Common polarity 
electrodes 106 are formed as a single part so as to reduce the number of 
wires within the handpiece. At the rear of the transducer is a feedback 
piezoelectric crystal 112 which is mechanically coupled to the driving 
crystals of the transducer and is commonly grounded with the driving 
crystals. The feedback crystal also has a projecting electrode connected 
to an electrical line (not shown) for conveying the feedback signal to an 
electrical contact at the rear of the housing and thence, through a 
connector, to a control circuit. The entire piezoelectric assembly, 
including the driving and feedback crystals, is electrically insulated 
from the front driver 107 and the rear driver 132 by insulating ceramic 
elements 108 and an insulating sleeve 109. The driving crystals, feedback 
crystal and associated electrodes are electrically insulated on both the 
inside and outside with a polymeric coating to prevent dielectric 
breakdown across the crystals and across the insulating ceramic elements 
108. 
The transducer also has a projecting electrode 133 connected to an 
electrical line (not shown) for conveying high frequency electrical energy 
to the front driver 107 for the purpose of tissue dissection or 
desiccation. 
The front end of the transducer terminates in a toroidal flange 113 which 
is mounted in a rubber mount 114 bearing against the inner wall of the 
housing and a steel washer 115. The rear end of the transducer is attached 
through a vibration isolation joint to a contact plate 116 which is 
hermetically bonded into the housing 110. 
Electrical lines from the piezoelectric driving crystals and feedback 
crystal terminate in electrical contacts 117 (FIG. 6) at the rear end of 
the housing. The electrical contacts operatively engages with 
complementary sockets in a connector 118 when the connector is connected 
to the housing. The electrical lines are connected to a generator and 
control circuit through a cable 120 attached to the rear end of the 
connector. The connector O-rings 133 isolate irrigation liquid, aspiration 
liquid and any liquid external to the handpiece from each other as well as 
from the electrical contacts. The connector 118 when connected to the 
handpiece simultaneously engages the ultrasonic power and feedback lines, 
the electrosurgery active wire, the aspiration tube and the irrigation 
tube. This the handpiece may be sterilized independent of any cabling. 
Attached to the front end of the transducer is a hollow tool 121 having a 
distal tip which is capable of fragmenting tissue when the tool is 
ultrasonically vibrated by the transducer. The proximal end of the tool is 
threaded and a hexagonal periphery 122 adjacent the proximal end enables 
the tool to be threadably engaged to a cooperating thread in a front plate 
attached to a flange 113 at the front end of the transducer. A washer 124 
around the front plate bears against a rubber mount 114 so that the 
combination of mount plates and washers forms a liquid-tight seal about 
the front end of the transducer. This seal is essential to prevent any 
irrigation liquid from entering the part of the housing which contains the 
transducer and the electrical components associated therewith. 
Irrigation liquid, usually saline solution, is conveyed to the tool tip 
through a channel 125 formed between the inner wall of a flue 126 and the 
outer wall of the tool 121. The irrigation liquid reaches the channel 125 
from a conduit 127 passing along the lower part of the housing, which 
conduit is supplied from an external reservoir through a tube (not shown) 
terminating in the connector 118. 
The tool 121 is hollow to allow fragmented tissue to be aspirated from the 
operation site. Aspiration is normally conducted by suction through the 
hollow tool and through a tube 128 (FIG. 5 and FIG. 6) passing axially 
through the housing and out through the connector. 
Since the irrigation liquid, which may be conductive, may have the 
electrical potential of the high frequency energy applied to the front 
driver, sufficient insulation distance is required for operator safety at 
the detachable connection points. Thus, a flue 126 is designed to shroud 
the housing 110 for a regulatory required insulation tracking distance. 
Likewise, the connector 118 also may shroud the housing 110 to achieve the 
required insulation tracking distance. 
In the embodiment illustrated in the drawings the handpiece is hand 
operated and a switch module 129 is mounted on the housing. The 
illustrated module contains two switches which are electrically connected 
to a circuit board within the housing for operating the handpiece. It is 
to be understood that a handpiece used in the apparatus of the invention 
may have more than two hand switches or may be operated by a foot switch.