Patent Application
20220079710
The invention relates to a dental handpiece for alternately receiving rotatable dental tools, e.g. dental drills, and a push button for such a dental handpiece for operating the tool clamping system to clamp and unclamp the rotatable dental tool.
Dental instruments typically include a base station that provides power, water, compressed air, and/or light and supplies those via a supply hose to a dental handpiece. The dental handpiece is typically coupled to a coupling piece by means of a standard interface, e.g. an ISO interface, located at the free end of the supply hose. Typical types of dental handpieces are on the one hand flow-driven dental handpieces, so-called turbines, and on the other hand motor-driven dental handpieces, which are, if they are operated by an electric motor, also referred to as electrical handpieces or electric contra-angles.
A dental handpiece typically comprises a rod-like handle, wherein a head of the dental handpiece with the tool holder is arranged at the front end of the rod-like handle. At the other end of the rod-like handle opposite to the head, a coupling element is arranged for coupling to the coupling piece of the supply hose.
In an electric motor-driven dental handpiece, the electric motor is typically located in the hose-side coupling piece and the rotation of the motor is transmitted to the head via a shaft in the rod-like handle. E.g. a spur gear is located in the head for driving the tool clamping device with the dental tool, e.g. a dental drill, clamped therein.
In a flow-driven dental handpiece, typically a turbine wheel is located in the head, on which compressed air is directed through a compressed air supply line via the supply hose, the coupling, and the rod-shaped handle. The turbine wheel then drives, typically directly coaxially, the tool clamping device with the dental tool. Depending on the design and operating pressure, flow-driven dental handpieces typically reach rotational speeds of about 150,000 to about 450,000 min−1. Typical motor speeds of motorized handpieces are in the range of up to 40,000 min−1, wherein handpieces having different gear ratios, e.g. 1:5, are available so that the rotational speed of the drill can be up to 200,000 min−1.
The head of the dental handpiece comprises a housing in which the tool clamping device, the turbine wheel or gear, the bearings, and the trigger mechanism for the tool clamping device, etc. are arranged. The housing of the head is typically substantially cylindrical and tapers to the side on which the dental tool is clamped. A cover, which is designed as a push button is typically arranged at the axial end of the head which is opposite to the tool holder, and which is referred to herein, without loss of generality, as the upper end. An actuating mechanism to change the dental tools is actuated by the push button. The push button is thus part of a cover system, which is typically fastened to the housing of the head by means of a thread.
The push button acting as an actuation element is typically designed as a hat-shaped metal cap and is mounted axially movable. A spring for generating a bias for the push button is typically located below the push button. By pressing the push button, the push button is moved axially and, after passing through a predefined idle stroke, comes into contact with the trigger mechanism of the tool clamping device, more precisely with a rotatable plunger. Upon further axial displacement of the push button by the user against the bias, the plunger is then moved relative to the shaft and transfers the tool clamping device in a release state in which the drill can be conveniently inserted and removed.
As already stated above, the push button is usually biased by a spring so that it cannot come into contact with the plunger without actuation during the dental preparation. On the other hand, this biasing spring is typically designed relatively soft, so that the operating forces for the user are not unnecessarily high.
Normally, the push button or the actuating mechanism should only be operated when the tool holder stands still. Nevertheless, it can still happen in the preparation that the dentist touches for example the cheek or a tooth of the patient with the push button while the motor is running. Although this is generally undesirable, it may happen that the push button is at least partially actuated against the bias of the spring and in an unfavorable event even to the extent that the push button touches the plunger. The contact between the push button and the plunger produces frictional heat, which is generally undesirable, and which depends on the contact surface, the contact pressure, the surface conditions of the contact surfaces, the speed, and the duration of the contact. This frictional heat can lead to an undesirable increase in temperature of the outer surface of the push button, under certain circumstances already after a relatively short time, typically after a few seconds.
Therefore, it is desirable to provide a construction which prevents excessive temperature rise of the outer surface of the push button even in the event of an unintentional actuation of the push button.
A conceivable possibility would be to make the biasing spring stiffer. However, this has the disadvantage that the actuating forces for the user to change the tools are also increased.
Further, it is known to use a blocking device with a tubular link having, in the vicinity of its end, a ball which is arranged opposite the push button, and which has a support plate for axially contacting the ball for this purpose. However, the contact plate used for this purpose, has a relatively small outer diameter compared to the push button. Furthermore, in such a construction it is not apparent, if and potentially how a contact between the push button and the contact plate close to the center could be prevented. Even if the heat transfer between the contact plate and the push button would take place on the outermost edge of the contact plate, the frictional heat generated in a presumed contact would be delivered relatively centrally to the push button, since the contact plate is small compared to the push button.
Another solution provides that a spherical element, preferably a ball, is fixedly mounted on the push button, and the clamping device is actuated with the ball. A disc can be used as a counterbearing for the ball. For this purpose, the ball and the disc are made of a material having a high hardness of greater than 2,000 on the Vickers scale, in particular ceramic material. First, it is disadvantageous that the spherical element or the ball requires a highly increased vertical space. If, on the other hand, a very small ball were chosen, the contact forces would be very high.
This could result in a deformation of the counterbearing, if not both parts are made of suitably hard material, such as e.g. technical ceramics. However, this entails a high coefficient of friction, which in turn, disadvantageously, causes a significantly higher temperature development at the contact point. Furthermore, an undesirably high wear can occur.
After all, the previously known systems are in need of further improvement.
Therefore, it is an object of the invention to provide a dental handpiece in which the temperature increase of surfaces of the push button, which may come into contact with patient tissue, can be kept within acceptable limits, even if the push button might come into contact with rotating parts of the tool clamping system when the dental tool is in rotation, e.g. because the push button is undesirably actuated during operation of a drill.
Another aspect of the object is to keep away frictional heat, which is generated at the contact point between the push button and rotating parts of the tool clamping system, e.g. the plunger, from the upper side of the cover plate of the push button, if the push button might come into contact with rotating parts of the tool clamping system during rotation of the dental tool.
Another aspect of the object is to provide a dental handpiece which is low in wear, inexpensive to produce, and meets high safety and quality standards.
The object of the invention is achieved by the subject matter of the independent claims. Preferred embodiments of the invention are defined in the dependent claims.
According to the invention, a dental handpiece is provided having a head for alternately receiving rotatable dental tools. The dental handpiece may be designed as a flow-driven handpiece, often referred to as a turbine, or as a motorized or electrical handpiece.
For example, the dental handpiece may comprise a rod-like handle with a head in which a rotatable dental tool, e.g. a dental drill, is clamped, and an interface (e.g. an ISO interface) opposite the head, by means of which the handpiece can be coupled to a supply hose of a base unit, to be supplied by the base unit with energy, compressed air, rotational drive, light and/or water.
The dental handpiece further comprises a housing for accommodating the components of the head, e.g. a tool clamping device for clamping a dental tool to selectively clamp the desired tool, e.g. the desired drill, in the head.
To this, the head comprises a trigger mechanism in the housing, by means of which the clamping of the rotatable dental tool is releasable to allow for insertion of the dental tool into the tool clamping device and to remove it from the tool clamping device. Accordingly, with the trigger mechanism, the tool clamping device can be transferred from an operating state, in which the dental tool is clamped in the tool clamping device to be rotationally driven, to a release state, in which the rotatable dental tool can be inserted and removed.
To this, the desired dental tool is inserted into the housing of the head and thus in the tool clamping device and removed again, e.g. through an opening at the bottom of the housing, when the tool clamping device is in the release state.
The trigger mechanism is operated by means of a manually operable push button. In particular, the push button can be depressed with a finger of the user to actuate the trigger mechanism, i.e. to bring it into the release state, so that the user can insert e.g. a drill or remove the inserted drill.
The push button is double-walled with an outer cover plate and an inner contact element. The upper side of the outer cover plate of the push button serves to actuate the push button by the user, wherein the push button is pressed against a bias or preload which is produced, e.g. by means of a push button spring circumferentially extending around an actuator or plunger. Therefore, the upper side or upper surface of the outer cover plate can principally come into contact with the tissue of the patient during the treatment. When the user presses the push button against the bias or preload, an underside or lower surface of the inner contact element comes into contact with the actuator or plunger and actuates the trigger mechanism with the actuator or plunger upon advancing depression of the push button until the release state of the tool clamping device is reached. Therefore, the actuator or plunger can also be designated as linear actuator, release pin or tappet.
A thermal insulation layer extends sandwich-like between the outer cover plate and the inner contact element and effects a thermal decoupling of the outer cover plate from the inner contact element.
Advantageously, this may reduce the heat flow from the contact point between the inner contact element and the linear actuator or plunger in the axial direction to the outer cover plate of the push button, so that the temperature of the outer cover plate can be kept within acceptable limits, even if the push button might undesirably be actuated so far that it comes into frictional contact with the rotating linear actuator or plunger during the rotation of the tool.
Preferably, the thermal insulation layer is formed as a thermally insulating gap or cavity extending in both dimensions of a plane transverse to the axis of rotation of the rotatable dental tool between an underside or lower surface of the outer cover plate and an upper side or upper surface of the inner contact element. The thermally insulating cavity may be gas filled, according to a simple embodiment e.g. air-filled, or evacuated or filled with a thermal insulation material. E.g. polyetheretherketone (PEEK) or ceramic material with low thermal conductivity may be considered as thermal insulation material for filling.
Preferably, the spatial extension of the thermal insulation layer or the thermally insulating cavity, at least in one direction, preferably in both directions in the plane transverse to the axis of rotation of the rotatable dental tool and the actuator or plunger corresponds to at least 40%, preferably at least 50%, preferably at least 70%, of the (inner) diameter of the push button. This can ensure that the heat generated at the contact point between the inner contact element and the actuator or plunger, can be dissipated preferably far radially outwards. This provides dissipation of the heat in the peripheral area of the push button.
The inner contact element and the thermal insulation layer thus preferably extend into the radial periphery of the push button. As a result, the thermal bridge between the inner contact element and the push button is preferably located in the radial periphery of the push button.
Therewith, in relation to the path that the heat flow must take from the contact point to the center of the outer cover plate, a detour is created, which can slow down the temperature rise there.
Furthermore, a better distribution of the heat energy over the surface of the push button is effected, resulting in a reduction of the local maximum temperature.
When the actuator or plunger rotates and the underside of the inner contact element contacts the rotating actuator or plunger at a contact point, frictional heat is generated involuntarily at the contact point in the inner contact element. This frictional heat is preferably dissipated in the inner contact element from the contact point predominantly radially outwards, i.e. in the plane transverse to the axis of rotation.
Preferably, the push button is hat-shaped, such that a peripheral circumferential wall surrounding the axis of rotation extends downwards from the outer cover plate in the direction of the tool holder. The inner contact element preferably extends into the peripheral region of the outer cover plate, if appropriate, up to the circumferential wall.
If the inner contact element extends radially far outward, if appropriate up to the circumferential or annular wall, and abuts on the annular wall or is joined to the push button at or in the vicinity of the annular wall, the heat can be dissipated up to this radially outer region.
The thermal insulation layer or the thermally insulating gap or cavity extends in an advantageous manner also into the radial periphery or the peripheral edge region of the hat-shaped push button, if appropriate up to the circumferential wall or circumferential ring wall.
Accordingly, the thermal coupling of the inner contact element to the push button is located in a region of the push button, where a patient contact is relatively unlikely. The path for the generated heat up to the outer cover plate is lengthened and thus slows down an increase in temperature on the upper side of the push button.
Preferably, the thermal insulation layer has a diameter of at least 2 mm, preferably at least 3 mm, preferably at least 4 mm, in the plane transverse to the axis of rotation. For example, the thermal insulation layer has a diameter of 4.7 mm+/−1 mm in the plane transverse to the axis of rotation. Further preferably, the inner contact element has a diameter of at least 2 mm, preferably at least 3 mm, preferably at least 4 mm in the plane transverse to the axis of rotation. For example, the inner contact element has a diameter of 5.8 mm+/−1 mm in the plane transverse to the axis of rotation.
Preferably, the inner contact element extends radially at least so far outward, or has a diameter which is at least so large, that the spring engages the inner contact element from below.
Further preferably, the material and the thickness of the inner contact element are selected or dimensioned such that the inner contact element does not bend upon actuation or at least such that the inner contact element does not touch the outer cover plate. For example, the thermal insulation layer, e.g. the air gap, has a thickness of 0.12 mm and the inner contact element has a thickness of 0.4 mm.
According to a preferred embodiment, the material and the machining of the inner contact element and/or of the actuator or plunger are selected such that the inner contact element and/or the actuator or plunger have a surface roughness with an average or mean surface roughness (Rz) of Rz<3.5 μm, preferably Rz<2.5 μm, preferably in the range of Rz=1.5 μm+/−1 μm at the contact point. Further preferably, the profile depth (Pt) of the inner contact element and/or of the actuator or plunger is Pt<6 μm, preferably Pt<4.5 μm, preferably in the range of Pt=3 μm+/−1.5 μm at the contact point.
Further preferably, at the contact point of the underside of the inner contact element with the actuator or plunger, the sliding (kinetic) friction coefficient μ (dry) is less than or equal to 0.3, preferably less than or equal to 0.25, preferably in the range of 0.18+/−0.05. In operation, however, the area in the push button is typically lubricated so that the friction levels in operation with lubrication are lower.
The use of material and processing technology to achieve a low surface roughness and low profile depth or having a low coefficient of sliding (kinetic) friction p (dry) has the advantage that the wear can still be kept low even with repeated actuation with a rotating motor or drive. The solution presented here can thus synergistically reconcile opposed requirements, such as low heating of the outer cover plate and wear resistance.
The heating of the outer cover plate can be further kept low, if the inner contact element is made of a material having a thermal conductivity of less than or equal to 30 W/(mK), preferably in the range between 10 W/(mK) and 25 W/(mK), preferably in the range of 15 W/(mK)+/−5 W/(mK).
In the context of the present invention it is possible to produce the inner contact element out of metal, for example out of acid- and rust-resistant steel. According to a preferred embodiment, the inner contact element consists of a steel with a martensitic structure. Also, the head of the actuator or plunger, which forms the upper end of the actuator or plunger and which comes into contact with the inner contact element, may be made out of metal, for example of acid- and rust-resistant steel. Thus, a metal-to-metal contact can be provided at the contact point between the inner cover plate and the actuator or plunger. For example, the inner contact element made out of metal directly contacts and actuates the head of the actuator or plunger without the need for additional spherical elements. Steel with martensitic structure and a hardness of about 760+/−50 HV3 is particularly preferred for the inner contact element.
The underside of the inner contact element and/or the upper end of the actuator or plunger are preferably machined by a turning lathe, at least by means of normal turning, but more preferred by precision turning.
This has the advantage that the sliding friction or kinetic friction is relatively low and the arrangement is low-wear and therefore durable. Furthermore, the production is simple and inexpensive.
Accordingly, the material of the inner contact element may have a hardness which is high compared to other metals, but relatively low compared to some other materials.
The Vickers hardness of the material of the inner contact element and/or the upper end of the actuator or plunger may be 1500 HV3, preferably 1200 HV3, preferably 900 HV3, preferably 550 HV3, preferably 700 HV3, e.g. in the range from 550 HV3 to 850 HV3, particularly preferred materials are in the range between 700 HV3 and 800 HV3.
Advantageously, an unacceptable plastic deformation of the contact area or the formation of a actuator or plunger impression at the contact point can be avoided. Therewith, the formation of an excessively enlarged contact surface can be avoided, whereby an increase of the heat development at the contact point can be kept within acceptable limits.
The inner contact element may be etched, e.g. as a contact plate out of a sheet metal foil, preferably out of a stainless steel foil, preferably out of a sheet metal foil of martensitic stainless steel, which is easy to manufacture. Furthermore, the use of such a sheet metal part or stainless steel sheet part is inexpensive.
Furthermore, the use of metal or stainless steel allows economical assembly, e.g. by pressing or welding the inner contact element in the push button.
The thickness (dimension along the axis of rotation) of the inner contact element at the contact point between the inner contact element and the rotating actuator or plunger is preferably less than or equal to 1 mm, preferably less than or equal to 0.6 mm, preferably less than or equal to 0.5 mm, preferably between 0.1 mm and 0.6 mm, preferably in the range of 0.4 mm+/−0.2 mm or +/−0.1 mm.
Furthermore, the thickness (dimension along the axis of rotation) of the thermal insulation layer or of the thermally insulating gap or cavity, in particular in the region of the axis of rotation, is preferably less than or equal to 0.5 mm, preferably less than or equal to 0.3 mm, preferably less than or equal to 0.2 mm, preferably between 0.01 mm and 0.2 mm, preferably in the range of 0.12 mm+/−0.05 mm or +/−0.03 mm.
Advantageously, the additionally introduced element in the form of the inner contact element and the thermal insulation layer or cavity generate only a slight increase in the height of the head, so that the overall height can be kept low.
Preferably, the sum of the thicknesses of the inner contact element and the thermal insulation layer is preferably less than or equal to 1.5 mm, preferably less than or equal to 1 mm, preferably less than or equal to 0.75 mm, preferably less than or equal to 0.6 mm, preferably in the range of 0.5 mm+/−0.15 mm.
All the aforementioned thickness values relate in particular to the central or near-axis region of the push button, in particular to the contact point with the head of the actuator or plunger.
If the inner contact element is made as a metal part which is separate from the outer cover plate, it can preferably be joined to the outer cover plate or other parts of the push button by a material bond, for example by welding, or by press-fit, or the inner contact element can be positively connected with the outer cover plate or other parts of the push button.
If the inner contact element is designed as a separate part from the outer cover plate, the push button preferably has an annular stop on the outer cover plate, in particular in the peripheral region of the outer cover plate, or on the circumferential (annular) wall. The inner contact element then rests against the annular stop, so that the thermally insulating cavity or gap is formed in the interior region of the annular stop.
The inner contact element may either lie loose in the hat-shaped push button and may be pushed against the annular stop by a spring, in particular by the spring which generates the bias of the push button for the operation of the trigger mechanism. On the other hand, the inner contact element may be pressed into the hat-shaped push button by means of a press-fit or may be joined to the hat-shaped push button by a material bond, for example by welding. In either case, a thermal bridge is created between the peripheral region of the inner contact element and the annular stop so that the heat which is conducted radially outwardly in the inner contact element is dissipated via the thermal bridge to the annular stop and from there into the peripheral outer region of the push button.
According to a preferred embodiment, the inner contact element may have a peripheral support ring, a central actuation field and a plurality of spokes, wherein the central actuation field is suspended by means of the spokes in the peripheral support ring, so that recesses exist between the spokes. Further preferably, the spokes may run not radially straight, but may be e.g. S-shaped, to increase the length of the path for the heat flow from the contact point between the actuator or plunger and the inner contact element to the peripheral support ring.
A further subject matter of the invention is the push button adapted for installation in the head of the dental handpiece for alternately receiving dental tools and for actuating a trigger mechanism in the head for clamping and releasing a dental tool,
If appropriate, such a push button can be installed as retrofit component in already existing handpieces. This seems possible in particular due to the low overall height of the present construction.
In the following the invention will be explained in more detail by means of exemplary embodiments and with reference to the figures, wherein identical and similar elements are partially provided with the same reference numerals, and wherein the features of different embodiments may be combined.
It is shown in:
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At the upper end of the head 12 is a cover system or lid system 30 with a threaded sleeve 32 which is screwed into an internal thread 34 of the head housing 14 from above. In the threaded sleeve 32, a cover or lid is used as a push button 36, which is axially (relative to the axis of rotation 38 of the tool) displaceable or movable. In this example, the cover or push button 36 is hat-shaped with an upper or outer cover wall or plate 42, which is slightly curved to the outside on the upper side in this example, and with an annular wall 48 or jacket, which adjoins the peripheral edge portion 44 of the outer cover plate 42 and extends axially with respect to the axis of rotation 38 downwardly from the peripheral edge portion 44. At the lower end of the annular wall 48, which is the free end of the annular wall 48 opposite to the outer cover plate 42, the annular or circumferential wall 48 has an outer collar or stop ring 50 which, in this example, provides an upper stop against an inner stop ring 52 of the threaded sleeve 32, and which holds the lid or push button 36 in the head housing or in the threaded sleeve 32.
The push button 36 is double-walled in a plane transverse to the axis of rotation 38, wherein the outer cover plate 42 forms a first layer of the two layers of the double wall. The second layer of the two layers of the double wall is formed by an inner contact member or inner contact element 54, in this example in the form of an inner contact plate, which is inserted from below into the hat-shaped cover or push button 36. The push button 36 is biased by a coil spring 56, which is supported at its lower end on an end plate 58 and at its upper end at the underside 54a of the inner contact plate 54. More generally, the spring 56 engages the inner contact element or plate 54. The bias of the spring 56 results in an actuating force for the push button 36 approximately in the range of 1 N to 5 N in the idle stroke range until touching the plunger head 62. The actuating force for actuating the trigger mechanism, however, is about 50 N.
To clamp the dental tool 8, the user typically pushes with a finger on the upper side 42b of the outer cover plate 42 to depress the push button 36 axially against the bias of the push button spring 56. In doing so, the user first overcomes the idle stroke between the underside 54a of the inner contact plate 54 and the plunger head 62, which forms the free upper end of the plunger 18, until the underside or lower surface 54a contacts the free upper end of the plunger 18. As the plunger head 62 or the free upper end of the plunger 18 is formed convexly, a relatively small contact point 64 between the inner contact plate 54 and the plunger head 62 is created. If the user pushes the push button 36 further down, the push button 36 actuates the plunger 18, i.e. pushes the plunger 18 downwards, by means of the pressure of the inner contact plate 54 on the plunger head 62, whereby the trigger mechanism of the tool clamping device 16 is actuated. When the trigger mechanism of the tool clamping device 16 is actuated, the tool clamping device 16 is in a release state (not shown) in which the dental tool 8, e.g. a dental drill, can be inserted or removed in the tool clamping device 16 (not shown).
An outer collar 66 on the ball bearing sleeve 22 forms a lower stop for the push button 36, which is put like a hat over the ball bearing sleeve 22 and on further actuation over the ball bearing 20.
In the present exemplary embodiment, the outer cover plate 42 has, on its underside 42a, a recess 70 with a diameter d=4.7 mm. The diameter of the inner contact plate 54 in this example is D=5.8 mm.
The central recess 70 is bounded outwards by a peripheral circumferential shoulder or ledge 72, so that an annular step 74 is formed at the outer circumference of the recess 70. Accordingly, the underside or lower surface 42a of the outer cover plate 42 has a peripheral support or bearing surface 76 for the inner contact plate 54. Accordingly, the inner contact plate 54 peripherally annularly engages the outer cover plate 42 from below and thereby forms the inner second layer of the double wall in the centrally double-walled region of push button 36.
Thus, the recess 70 forms a central gap or cavity 78 which extends in both dimensions in the plane transverse to the axis of rotation 38 between the outer cover plate 42 and the inner contact plate 54. In the present example, the cavity 78 is unfilled, i.e. air under atmospheric pressure is present in the cavity 78. Thus, the cavity 78 forms a thermal insulation layer 80, which extends flatly in the two dimensions of the plane transverse to the axis of rotation 38 between the outer cover plate 42 and the inner contact plate 54, and effects a thermal insulation against heat flow from the inner contact plate 54 to the outer cover plate 42 in a central region 82 of the push button 36. The contact between the inner contact plate 54 and the peripheral annular support or bearing surface 76 creates a thermal bridge 84 from the inner contact plate 54 to the push button 36 or, in this example, to the outer cover plate 42. Thus, the thermal bridge 84 is not in the central or near-axis region 82 of the push button 36 or the outer cover plate 42, but in the peripheral edge portion or region 44 of the outer cover plate 42, i.e. in the radial periphery 37 of the push button 36.
If the push button 36 is undesirably actuated during rotation of the plunger 18, e.g. accidentally actuated so far that the inner contact plate 54 might come into contact with the plunger head 62 at the central contact point 64, frictional heat is initially generated at the central contact point 64. The thermal conductivity of the material of the inner contact plate 54 is higher than the thermal conductivity of the thermal insulation layer 80, which is, in this example, an air layer. Therefore, the frictional heat generated at the contact point 64 is guided predominantly or essentially radially outwards within the inner contact plate 54. The annular contact region 85 between the upper side or upper surface 54b of the inner contact plate 54 and the outer cover plate 42, which forms the thermal bridge 84 between the inner contact plate 54 and the push button 36, is located peripherally relatively far away from the rotation axis 38 so that the generated frictional heat is distributed peripherally on a relatively large perimeter into the peripheral edge region 44 of the outer cover plate 42. This provides, inter alia, that the maximum temperature of the upper side or upper surface 42b of the outer cover plate 42 remains within acceptable limits in the areas which are in danger of being touched. In the example shown in
In other words, the inner contact element 54 and the thermal insulation layer 80 extend radially into the radial periphery 37 of the push button 36, so that the thermal bridge 84 is located in the radial periphery 37 of the push button 36.
In the present example, the diameter d of the thermal insulation layer 80 is about 75% of the inner diameter Di of the push button 36. Preferably, this ratio d/Di may be at least 40%, at least 50% or at least 70%.
In the example shown in
The use of an acid- and rust-resistant martensitic stainless steel for the inner contact plate 54 advantageously provides a high strength or stability against deformation with a comparatively small thickness h. Furthermore, such a martensitic steel advantageously has a smooth or even surface, so that a relatively lower coefficient of friction is provided at the contact point 64 with the plunger head 62. The plunger head 62 is also made of an acid- and rust-resistant steel, so that in this example there is a steel-to-steel contact at the central contact point 64. In particular, the inner contact plate 54 directly contacts and actuates the plunger head 62 without the need for additional spherical elements. As a result, the heat development can be reduced already at the contact point 64 with respect to materials having a higher coefficient of friction. In addition, the inner contact plate 54 made of such a martensitic steel is easy to process and may be produced precisely and inexpensively by etching. At the same time, the acid- and rust-resistant, preferably martensitic, steel used for this example has a coefficient of thermal conduction λ=15 W/(mK), which is relatively low compared to other steels.
In particular, the relatively low thermal conductivity, the low coefficient of friction and the predominantly radial heat dissipation into the peripheral edge region 44 or in the radial periphery 37 of the push button 36 synergistically interact, so that the maximum temperature at points of the push button 36, which are in danger of being touched, can be kept within acceptable limits even at a long-term contact of the inner contact plate 54 with the plunger head 62 under the maximum possible contact pressure.
In the push button 36, the inner contact plate 54 engages the peripheral bearing surface 76, which surrounds the cavity 78 and forms a peripheral annular stop. In this example, the annular wall 48 or jacket of the push button 36 has a peripheral shoulder or ledge 77 which centers the inner contact plate 54 and forms an annular press fit or interference fit 86. In this example, the inner contact plate 54 has on its underside 54a an annular extension 55, which centers the spring 56, but may also contribute to increase the flexural rigidity of the inner contact plate 54.
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In this example, the gap or cavity 78 between the inner contact element 54 and the push button 36, forming the thermal insulation layer 80, also has two areas, namely a base portion 114 extending in the plane transverse to the axis of rotation 38 and a jacket area or shell portion 116 located between the peripheral annular walls 48 and 108. In other words, in this example, the thermal insulation layer 80 is also hat-shaped.
Optionally, the outer cover plate 42 may have a thinning 71, which increases the thickness H of the thermal insulation layer 80 and forms a safety margin against deformation.
In the embodiment of
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Although the use of hardened martensitic stainless steel for the inner contact plate 54 has advantages due to the low coefficients of friction with the plunger head 62, it shall not be excluded that the inner contact element or inner contact plate 54 may be made out of austenitic (acid- and rust-resistant) steel or out of a ceramic material. Although, ceramic materials typically provide a higher coefficient of friction, this may nevertheless be acceptable, if the thermal bridge 84 between the inner contact plate 54 and the push button 36 is located in the radial periphery 37 of the push button 36.
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It should be noted that the directional information like above or below, left or right, are not absolute, but refer to the orientation shown in the figures of the dental handpiece 10 and push button 36, in which the push button 36 is located above and the clamped dental tool 8 is located below.
It is apparent to those skilled in the art that the above-described embodiments are to be understood as exemplary and that the invention is not limited to these embodiments, but may be varied in many ways without departing from the scope of the claims. Furthermore, it will be understood that the features, whether disclosed in the specification, the claims, the figures, or otherwise, do individually define essential components of the invention, even if described together with other features. Thus, every such feature is to be understood to be disclosed separately and independent of each other. The description of features of each embodiment also applies to each of the other embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18210550.2 | Dec 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/083873 | 12/5/2019 | WO | 00 |
