Note: Descriptions are shown in the official language in which they were submitted.
CA 02263269 1999-03-O1
a
- ' DEVICE FOR CURING WITH LIGHT
Background of the Invention
The ptresent invention relates to a curing device employing
light, especially for the polymerization of dental materials by light,
comprising a hand-held device with light source that is connected by
a cable to a supply station whereby the cable is detachable and can
be plugged into the hand-held apparatus and the supply station. A
control unit for the light source is provided in order to ensure a
uniform light emission or intensity.
Various curing devices for curing by light are known which
are means-powered and which are used for the light-induced
polymerization of dental materials. A hand-held apparatus receives
the light source and connected by a cable to the supply station.
Such curing devices have the advantage, in comparison to battery-
operated curing devices, that a higher light output can be provided
and that the hand-held apparatus itself is fight-weight since the
weight of the battery or accumulator has been eliminated.
(n known curing devices the supply voltage for the light
source in the supply station ~is stabilized in a manner known per se
20' by a voltage controller. In these curing devices it is assumed that
a voltage stabilization over the service life of the light source is
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~ sufficient in order to provide to sufficient light output for
polymerization. (n addition, it has been known to measure the light
output of the hand-held apparatus whereby one example for such
a light-curing device is known from German Gebrauchsmuster 8212
892. In this curing device the supply station is provided with a light
sensor which responds when the detected light is of sufficient
intensity.
This solution however is disadvantageous because the action
of monitoring whether the curing device still functions reliably is in
the hands of the operator. Accordingly, different levels of
responsibility on the user's part thus has a strong effect on the
reliability of the device so that the manufacturers of such devices
recommend to exchange the light source or lamp as a matter of
precaution after about 100 hours of operating time.
Light sources which, for example, may be in the form halogen
lamps are disposable items. However, there are considerable
quality differences and thus differences in their service life. For
example, for the same operating parameters, a lamp with a high-
quality coil which is comprised of wire that is of uniform thickness
and uniform roundness, may last three times longer than a light
source of lower quality. However, whereby in known devices the
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CA 02263269 1999-03-O1
- improved service life of such high-quality sight sources, which have
also essentially a well defined spectrum, cannot be fully used for the
aforementioned reasons.
A further disadvantage of such light curing devices is that
5, they can be adapted only with difficulty to the IoCal particularities of
respective dental practices. White in some practices it is more
' favorable to arrange the supply station directly adjacent to the hand-
held apparatus, such that a short cable is sufficient, in other
practices the local particularities are such that an arrangement of
supply station and of the hand-held apparatus spaced far apart is
necessary.
These requirements of dental practices can be taken into
consideration with known light curing devices only to a limited
extent. The length of the cable may not surpass a certain limit in
order not to impede the light intensity to be provided. On the other
hand, the cable should not be too thick in order to provide the
desired flexibility and bending ability so that in the past relatively
Limited minimum and maximum cable lengths have been provided.
Furthermore, when supplying such curing devices, it must be
specified which length of cable is desired in order to be able to
adapt the light source control to the cable length. 'this must be
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I
- performed by the manufacturer so that when the special
requirements within the dental practice change or when it is
determined that the initially ordered cable length is not sufficient, a
complicated exchange with manipulations of the device by a service
technician must be pertom~ed.
It is therefore an object of the present invention to provide a
curing device of the aforementioned kind with improved economic
use and greater flexibility with respect to its use.
Summary of the Invention
A curing device for curing dental materials by light-induced
polymerization is primarily characterized by:
a supply station; .
a hand-held apparatus comprising a light source;
a detachable cable connecting the hand-held apparatus to
the supply station;
an output control device controlling the light source in order
to ensure a uniform light intensity, wherein the output Control device
a preset nominal output;
the output control device comprising a Control FET;
the cable connected within the output control device;
wherein the output control device prevents switching on the
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curing device or emits a warning signal when the nominal output
requires a voltage, surpassing a control biases voltage minus a
potential difference of the control FET, or a corresponding current.
Advantageously, the cable comprises a control line. The
output control device preferably has a voltage sensor for detecting
a terminal voltage of the light source and producing a terminal
voltage signal. The output control device also may comprise a
current sensor for detecting a current of the light source and
producing a current signal. The output control device further
includes an evaluation circuit. The terminal voltage signal and the
current signal are supplied via the evaluation circuit to the control
line of the Cable.
Preferably, the cable comprises a control line and the supply
station comprises a control circuit embodied as a switch control for
~ controlling the control FET. The control circuit is preferably
connected to the control line.
Expediently, the hand-held apparatus comprises a calibrating
unit for calibrating the current sensor, the voltage sensor, and the
evaluation circuit.
The evaluation circuit.preferably comprises a dclac converter
calibrated by the calibrating unit. .
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The hand-held apparatus has preferably a startlstop switch
connected to the evaluation circuit, wherein the starflstop switch has
a keying function and, when actuated, delivers a start signal to a
control line.
Preferably, the control circuit has a control characteristic line
for linearly increasing with increasing control voltage the output
voltage beginning at a soft start value, wherein the output voltage is
supplied through the cable to the light source.
Advantageously, the slope of the control function of the
control circuit for controlling the control FET is slightly greater than
1.
'the output control device preferably compensates for
different lengths of the cable.
Advantageously, the hand-held apparatus includes a fan and
auxiliary devices. The control I=ET supplies a controlled output
voltage to the cable, and the fan and auxiliary devices are supplied
by the cable with an auxiliary output voltage that is independent of
the controlled output voltage.
The evacuation circuit has an output terminal for the fan for
activating the fan, wherein the activation period of the fan for cooling
the light source is determined by the evaluation circuit based on
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continuous or accumulated period of use of the light source.
The calibrating unit during calibration evaluates all
components of the hand-held apparatus that exhibit tolerances.
The calibrating unit includes a memory and the calibrating data are
stored in the memory. The hand-held apparatus is Calibratable
independent of the length of the cable.
Preferably, the memory is in EEPROM.
Preferably, the evaluation circuit comprises a signal device
for indicating that a lamp of the light source must be exchanged
when the inner resistance of the light source is outside of a
threshold value.
The threshold value is advantageously the controlled output
voltage defined as the control bias voltage plus a minimum potential
difference of the control f=ET.
Surprisingly, the inventive_ curing device provides a
substantially improved use of the light source so that it is
recommended to employ high-quality light sources having an
extended service life so that the maintenance intervals for the light
curing device can be extended substantially, for example, tripled.
The. inventive output control can be employed especially
advantageously when inventively a voltage adjustment according to
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- ttie inner resistance of the light source is provided.
The increase of the inner resistance is automatically
monitored whereby according to a preferred embodiment a signal
is emitted when the voltage adjustment no longer can provide a
voltage corresponding to the inner resistance which means that the
light source or lamp should be exchanged. The required nominal
output in this case can no longer be ensured. This embodiment
allows with especially simple but especially effective means a
service life monitoring action which is adapted to the changes of the
tungsten coils so that a portion of the service fife of the light source
is no longer wasted.
By including the cable it is not only possible to provide for a
more precise stabilization of the light o~rtput but it is also no longer
necessary to call a technician in order to adapt the light curing
device to the desired cable length. The output control detects
directly the voltage and current at the light source, i.e:, its operating
parameters, and then adjusts within the supply station that includes
the control member the curing device components relative to one
another. For this purpose, the cable contains an additional control
line which may be very thin and which therefore does not impede
the flexibility of the cable. Inventively, it is especially favorable that
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a cable that is comparatively thin and thus very flexible is employed
because its inner resistance can t?e fully controlled.
According to an especially advantageous embodiment it is
suggested that the cable is detachable and can be plugged into the
hand-held apparatus and the supply station so that the dentist or the
dental assistant can perform an adaptation of the light curing device
to the desired cable length. Such cables can be ready made
whereby employing standardized plugs and sockets make it
possible to use pre-manufactured cables which are inexpensive.
In a preferred embodiment it is suggested to provide a
second controlled auxiliary supply voltage that is independent of the
controlled output voltage for supplying the lamp. The auxiliary
supply voltage supplies auxiliary elements such as a fan etc. and is
transmitted via a supply voltage line provided in the cable.
With such an independent auxiliary supply voltage tine an
improvement of the linear character of the control characteristic line
for the output voltage, i.e., for supplying the light source, can be
achieved whereby moreover the action of switching on the auxiliary
elements will not disrupt the control circuit.
Brief Description of the Drawings
The object and advantages of the present invention will
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CA 02263269 1999-03-O1
- appear more clearly from the following specification in conjunction
with the 2~ccompanying drawings, in which:
Fig. 1 is a perspective view of the inventive light
curing device in one embodiment;
Fig. 2 is a circuit diagram for representing the
electrical design of the light curing device in the
embodiment according to Fig. 1;
Fig. 3 shows the characteristic line for representing
the soft start for the inventive light curing
device.
Description of Preferred Embodiments
The present invention will now b~ described in detail with the
aid of several specific embodiments utilizing Figs. 1 through 3.
The light curing device represented in Fig. 1 comprises a
supply station 12 and a hand-held apparatus 14 connected to one
another by a cable 16. The Cable 16 is provided at its end with
plugs 18 and 20 which are received in respective sockets in the
hand-held apparatus 14 and the supply station 12. The socket 22
at the supply station 12 can be seen in Fig. 1.
The cable 16 is a mufti-wire and highly flexible cable, and, as
shown in Fig. 1, is relatively thin. Its weight therefore does not
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imped manipulation of the hand-held apparatus 14. Conventional
cables used fior such devices, on ' the other hand, have for a
comparatively great flexibiNty, due #o the used amount of copper, a
'relativveely great weight. -
The hand-held appatatus 14 is essenSaNy pistol-shaped and
contains a light souroe 24 and a fan 28 which are shown in a
- . - dashed line. Also, a start/stop switch is proved whereby only the
button 28 is shown in F~g.1.
F'g. 2 shows the circuit diagram of the im~entlve Nght curing
device 10. 'the supply sta~vn 12 has, in a manner IalONVn per se,
an onloff switch 30 which is supplied with eles:tridty from the main
cable 32. The main voltage is transfdlmed to a secondary voltage
by an annular transformer 34 and is then rec:~ed by r~et~ifier 36 and
smoothed by a capac~ttor 38 ~ .~"~~e st~oo~thed voltage at the output
15' terminal of the recur 36 iS the input voltage, which is refen~ed to
as the control bias voltage 39, used for the control circuit 38, to be
desa~'bed in more detail in the following, as weN as for a faced
voltage controNer 40-which provides. the auxiliary supply voltage 42
transmitted via cable 16 to the hand-held apparatus 14.
- The control drcuit 38 yes a ~ control . -svvitd~ which is
connected to the control bias vdtage 39 and switd~s ~ response
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to an analog control signal, coming from the control line 44
extending through the cable 1fi, the control element 46. With this
type of control a loss-reduced supply may be ensured while, in
principle, it is also possible to use instead of the switching control a
simple longitudinal cohtrol. The control element 46 is preferably a
field effect transistor FAT which is connected to the control bias
voltage 39. The output voltage 54 of the control element 4B
includes, in a manner known per se, an impulse-pause ratio
depending on the control requirements so that substantially a
rectangular or trapezoidal voltage is provided. When switched on,
this output voltage corresponds to the control bias voltage 39 minus
the potential difference of the FET 4$. A negative preshooting of
the switching peaks can be avoided by diode 48 whereby it is
understood that w)th a corresponding diode connected to the input
voltage 39 a positive cwershooting can be avoided if needed. The
output current of the control element 46 is smoothed by a coil 50
and further smoothed by a filter capacitor or smoothing capacitor 52
to such an extent that the output voltage 54 with a required minimal
wave shape is provided and supplied to the cable 16.
In addition to the inventive control circuit it is suggested to
provide a second output control circuit directly adjacent to the
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switching control 38. With this control circuit the input current of the
line supplying the control voltage as well as the output voltage of the
control element 46 are detected and also employed for the control
action.
The cable 16 in the shown embodiment includes ten wires.
However, it would be sufficient to have~only four wires. One wire is
designed for transmitting the auxiliary voltage 42. A further wire is
provided as a control line 44. The remaining wires are divided onto
the contacts for the output voltage 54 and for ground 56 whereby in
the shown embodiment respectively four wires are used for these
lines. it is understood that an adaptation within wide specification
ranges is possible in this context. if needed, the cable 16 at the
side connected to the hand-held aaparatus may be provided with a
further filter capacitor between the output voltage 54 and ground 56
whereby the inner resistance of the cable 16 further improves the
smoothing of the output voltage. ,
The hand-held apparatus 14 employs the auxiliary supply
voltage 42 for supplying voltage to an evaluation circuit 60, for the
supply of the fan 26, for supplying a signal device 62 which may be
embodied as a piezo buzzer as well as for supplying the operating
display LED 64. These auxiliary elements 66 are thus taken out of
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the control circuit and therefore do not impede its linear action.
The light source 24 is connected via thermoswitch 68, which
is a safety element, and via a current sensor 70 to the output
voltage 54 and ground 56 at the secondary side of the cable 16, i.e.,
at the hand-held apparatus 42. The current sensor 70 comprises a
current measuring resistor with a resistor value which is matched to
the predetermined lamp power. For example, when the lamp has
a power of 75 watt, the resistance of the current sensor 70 may be
0.025 ohm. The voltage potential generated by the light source
current across the measuring resistor is detected by the current
sensor 70 and supplied to the evaluation circuit 60.
Furthermore, a voltage sensor 72 is provided which detects
the terminal voltage of the light source 24 as well as a further
voltage sensor 74 which is directly connected to the output voltage
54 so that the evaluation circuit 64 can also detect activation of the
thermoswitch 68 due to a difference of the output signal of the
voltage sensors 72 and 74.
The evaluation circuit 60 provides a multiplication product of
the detected voltage and current values of the sensor i 0 and 72
and is connected to the Control line 44 which is supplied with
respective initial signals so that the control circuit 38 in the supply
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station 12 can provide a control of the output voltage 54 according
to the respective power output nominal value of the evaluation
circuit 60.
Furthermore, a calibration device is provided. The calibration
device $0 comprises a start contact for compensation in which the
exact magnitude of the measuring resistance of the current sensor
70 but also the linear function of the dclac convertor in the
Pvaluation device 60 is memorized. The calibration device 80
comprises furthermore an EPROM that is contained v~iithin the
evaluation circuit 60 and has stored therein the respective
calibration curve. Calibration can be performed for the entire hand-
held apparatus 14 so that it is independent of the type and length of
the cable 16 being used.
The light curing device can be started and stopped by a
startlstop key $2 whereby the key 82 is actuated by the onloff switch
22. It is understood that the type of detecting of the relevant voltage
and current values can be adjusted within wide ranges of respective
specifications. For example, it is pbssible to employ a pure analog
control of the evaluation circuit 60 which provides for a continuous
voltage adjustment. However, a less expensive and more flexible
digital control is suffcient whereby the speed requirements with
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respect to the digitallanalog convertor ace limited since, for example,
' a voltage adjustment can be performed within intervals of 100 msec.
Inventively, it is especially advantageous when via the
start/stop key 82 is so-called soft start is realized. According to Fig.
3, when activating the onloff switch 28 predetermined voltage curve
can be realized within the evaluation circuit 60 which allows for an
. increase of the output voltage 54 within, for example, 3 seconds. In
Fig. 3 the output voltage 54 is represented as a function of the
control voltage 84 which is present at the control line 44. It is shown
that,the slope is slightly more than 1 beginning at a threshold value
of 2 Volt. Below a control voltage of 2 Volt the control circuit 38 is
turned off so that for the start/stop key 82 in its turned off position
no leak current flows through the light source 24. '
' Inventively, current and voltage can be simultaneously
measured whereby a measuring event is performed within a spacing
of a few nanoseconds. Preferably, measurement is performed at
uniform intervals whereby the interval length is determined by the
changing time of the digitallanalog convertor. It is also possible to
switch the input terminal of the convertor between current and
voltage measurement so that only one convertor is needed.
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