Patent Description:
An air turbine handpiece that cuts an affected part by a rotational force of an air turbine, and a motor handpiece that cuts an affected part by a driving force of a motor are known as dental handpieces. Each of these dental handpieces holds a dental treatment tool by a chuck mechanism housed in a head portion, and cuts the affected part by rotating the dental treatment tool at a high speed.

A technique has been proposed in which by preventing a reduction in chucking force of a chuck mechanism that holds a dental treatment tool, dropping out, idling, and the like of the dental treatment tool are prevented (for example, <CIT> and <CIT>).

<CIT> discloses a configuration in which the dental treatment tool (chucked member) is chucked by a ball that protrudes and retracts in a radial direction from a tubular chuck shaft.

<CIT> discloses a holding mechanism including: a tubular tool holding member that holds the dental treatment tool; a tapered member that is disposed outside the tool holding member; and a coil spring that biases the tool holding member upward. Slits are formed at three locations along a circumferential direction of the tool holding member, and small pieces are fitted into the respective slits. An outer peripheral surface of each of the small pieces comes into contact with the tapered member when the tool holding member receives a biasing force from the coil spring, and each small piece is pushed inward in a radial direction due to a wedge effect of a tapered surface. As a result, each small piece engages with the dental treatment tool, and the dental treatment tool is held in the tool holding member.

However, in the chuck mechanism described in <CIT>, the dental treatment tool is locally gripped by the ball, so that problems arise that wear easily occurs and a gripping force is easily reduced.

In <CIT>, a gripping force on the dental treatment tool depends on a frictional force of the tapered surface. Therefore, when a particularly strong vibration is, for example, applied to the tapered surface during cutting, a gap may be created between the dental treatment tool and the small piece, and the dental treatment tool may drop out of the tool holding member. Since the tapered member is thin-walled, a gradient of a taper is shallow, and biting on the tapered surface easily occurs. As a result, attachment and detachment failures of the dental treatment tool easily occur.

Therefore, an object of the present disclosure is to provide a dental handpiece capable of improving wear resistance of a chuck mechanism and always stably holding a dental treatment tool regardless of a cutting condition.

<CIT> discloses a chuck for receiving a plain shank of a dental burr. The chuck is rotatably mounted in the head of a dental handpiece and is driven by a pinion or by turbine vanes. The chuck comprises a sleeve adapted to receive the shank of a burr and provided with at least one elongate clamping claw which is movable radially between an inner clamping position and an outer releasing position. Facing grooves in the clamping claw and in an actuating member which is movable axially relative to the sleeve define a ramp way for a row of bearing balls. The ramp way extends in a direction which is generally axial but is inclined at an angle of <NUM> DEG to <NUM> DEG to the axis so that the clamping claw is moved radially by axial movement of the actuating member. The clamping claw is spring biased to a clamping position and is movable to releasing position by a push button for moving the actuating member axially relative to the sleeve and thereby moving the clamping claw radially outwardly.

<CIT> and <CIT> disclose a dental handpiece of the preamble of claim <NUM>.

According to the present invention, there is provided a dental handpiece as defined in appended claim <NUM>. Preferred features are set out in its dependent claims.

Hereinafter, embodiments of a dental handpiece according to the present disclosure will be described in detail with reference to the drawings. Here, a configuration example of an air turbine handpiece will be described, but a configuration of a motor handpiece or the like including another driving mechanism may be used.

<FIG> is an overall view of a dental handpiece <NUM> according to the present disclosure.

The dental handpiece <NUM> includes a head portion <NUM> and a grip portion <NUM> that extends rearward from the head portion <NUM>. The head portion <NUM> includes a chuck mechanism which will be described in detail later and in which a dental treatment tool <NUM> is mounted so as to be attachable and detachable, and rotatably drives the dental treatment tool <NUM> mounted in the chuck mechanism. In the configuration, a grip portion is provided with an air supply passage (not shown) and an exhaust passage (not shown) for compressed air, the dental treatment tool <NUM> is rotatably driven by the compressed air supplied from the air supply passage, and the compressed air used for driving is discharged through the exhaust passage.

<FIG> is a schematic cross-sectional view of the head portion <NUM> of the dental handpiece <NUM> shown in <FIG>. In the following description, an insertion and extraction direction of the dental treatment tool <NUM> when the dental treatment tool <NUM> is mounted in the head portion <NUM> is also referred to as an up and down direction or an insertion direction, a front in the insertion direction is also referred to as an upper side, and a rear in the insertion direction is also referred to as a lower side.

The head portion <NUM> is formed by being surrounded by: a head housing <NUM> that is connected to the grip portion <NUM> and covers an outer periphery of the head portion <NUM>; a head cap <NUM> that covers an upper portion of the head housing <NUM> and is fixed to the head housing <NUM>; and a push button <NUM> that covers a top of the head cap <NUM>. A biasing spring <NUM> is provided between the push button <NUM> and the head cap <NUM>, and the biasing spring <NUM> biases the push button <NUM> upward.

A cartridge case <NUM> is housed inside the head housing <NUM>. The cartridge case <NUM> is fixed integrally with the head housing <NUM> by assembling the head cap <NUM> from above the head housing <NUM>. Outer rings <NUM> of a pair of rolling bearings 31A and 31B are fixed to an inner peripheral side of the cartridge case <NUM>. Inner rings <NUM> of the rolling bearings 31A and 31B are fitted with an outer peripheral surface of a hollow cylindrical sleeve <NUM>.

The sleeve <NUM> is rotatably supported by the rolling bearings 31A and 31B, and the dental treatment tool <NUM> is inserted into the sleeve.

A rotor <NUM> is fixed between the rolling bearing 31A and the rolling bearing 31B on the sleeve <NUM>. The rotor <NUM> is a rotating body including a turbine blade, generates a rotational force by the compressed air supplied into the cartridge case <NUM>, and rotatably drives the sleeve <NUM>. That is, the sleeve <NUM> is supported by the head housing <NUM> and the cartridge case <NUM> through the rolling bearings 31A and 31B, so that the sleeve <NUM> rotates with the rotational force generated by the rotor <NUM> as a drive source.

The sleeve <NUM> includes a small diameter portion 37a and a large diameter portion 37b on an inner peripheral surface thereof. A coil spring <NUM>, which serves as an elastic biasing member that biases a cylindrical slide member <NUM> forward in the insertion direction of the dental treatment tool <NUM>, is disposed at a lower end of the large diameter portion 37b. The coil spring <NUM> has an inner diameter that allows the dental treatment tool <NUM> to be inserted through the coil spring <NUM> along an axis Lc of the sleeve <NUM>, and has a configuration in which space efficiency is improved in the sleeve <NUM>. A chuck mechanism <NUM> to be described below includes the sleeve <NUM> and members housed in the large diameter portion 37b of the sleeve <NUM>.

<FIG> is a partially enlarged cross-sectional view showing the chuck mechanism <NUM> housed in the sleeve <NUM>. <FIG> is an exploded view showing the members constituting the chuck mechanism <NUM>. In the following description, the same members or the same locations are denoted by the same reference numerals, so that descriptions thereof will be omitted or simplified.

The chuck mechanism <NUM> mainly includes the sleeve <NUM>, the cylindrical slide member <NUM>, a plurality of (two in the configuration) divided movable pieces 47A and 47B, the coil spring <NUM> described above, and a stopper unit <NUM> (see <FIG>).

The cylindrical slide member <NUM> is housed in the sleeve <NUM> so as to be movable in an axial direction of the sleeve <NUM>, and includes, on an inner peripheral surface thereof, a first tapered surface <NUM> whose diameter increases upward (forward in the insertion direction of the dental treatment tool <NUM>). The divided movable pieces 47A and 47B each include, on an outer peripheral surface thereof, a second tapered surface <NUM> that comes into sliding contact with the first tapered surface <NUM>.

The pair of divided movable pieces 47A and 47B are disposed so as to face each other in a diameter direction of the sleeve <NUM>, and independently rotate in the sleeve <NUM> together with a pusher <NUM> which will be described later.

The stopper unit <NUM> includes a cylindrical fixing member <NUM> that includes a third tapered surface <NUM> (third tapered surface) on an inner peripheral surface thereof, and a fourth tapered surface <NUM> provided on each of the divided movable pieces 47A and 47B. These tapered surfaces each have a gradient in a direction of the axis Lc, thereby functioning as tapered fitting portions that convert movement of the divided movable pieces 47A and 47B in the direction of the axis Lc into movement of the divided movable pieces 47A and 47B in a radial direction. As will be described in detail later, the stopper unit <NUM> is at least partially fixed to the sleeve <NUM>, and restricts forward axial movement of the divided movable pieces 47A and 47B in the insertion direction.

Furthermore, the pusher <NUM>, which is moved by the push button <NUM> that is pressed down when the dental treatment tool <NUM> is to be detached from the chuck mechanism <NUM>, is disposed above the divided movable pieces 47A and 47B. The pusher <NUM> includes a pair of push pieces <NUM> that extend toward the cylindrical slide member <NUM> through circumferential gaps between the divided movable pieces 47A and 47B.

An annular restriction ring <NUM> fixed to the sleeve <NUM> is disposed below the cylindrical fixing member <NUM> (at a rear end portion thereof in the insertion direction of the dental treatment tool <NUM>). The restriction ring <NUM> is held between a stepped portion <NUM> formed on the inner peripheral surface of the sleeve <NUM> and a lower end of the cylindrical fixing member <NUM>.

<FIG> is a perspective view of the divided movable pieces 47A and 47B.

The divided movable pieces 47A and 47B are disposed at different circumferential positions in the sleeve <NUM>, and have the same shape. The divided movable pieces 47A and 47B each include the outer peripheral surface that comes into contact with the inner peripheral surface of the cylindrical slide member <NUM>, and an inner peripheral surface that comes into contact with an outer peripheral surface of the dental treatment tool <NUM> inserted into the sleeve <NUM>, and the divided movable pieces 47A and 47B are disposed such that the dental treatment tool <NUM> is held therebetween.

The second tapered surface <NUM> and the fourth tapered surface <NUM>, which are gradually reduced in radius of an outer peripheral surface outward in the axial direction, are formed on one end side and the other end side of each of the divided movable pieces 47A and 47B in the axial direction. A recessed groove <NUM> along a circumferential direction is formed between the second tapered surface <NUM> and the fourth tapered surface <NUM>. A groove wall <NUM> on a second tapered surface <NUM> side and a groove wall <NUM> on a fourth tapered surface <NUM> side are formed by the recessed groove <NUM>. As shown in <FIG>, the restriction ring <NUM> is inserted into the recessed groove <NUM>. A cutout portion <NUM>, which gradually increases in radius of an inner peripheral surface outward in the axial direction, is formed at at least one end portion of the inner peripheral surface of each of the divided movable pieces 47A and 47B.

Each of the divided movable pieces 47A and 47B shown here has a symmetrical shape in which a plane passing through an axial center and perpendicular to the axial direction is used as a symmetry plane. Since the divided movable piece has the symmetrical shape, it is not necessary to consider directionality of the divided movable piece when the chuck mechanism <NUM> is assembled, and assembling workability may be improved.

<FIG> is a perspective view showing a state after the members shown in <FIG> are assembled. In <FIG>, the cylindrical fixing member <NUM> is not shown. In the pusher <NUM>, a tip end of each of the push pieces <NUM> disposed between the pair of divided movable pieces 47A and 47B is in contact with the cylindrical slide member <NUM>. By pressing the push button <NUM> down (see <FIG>), the cylindrical slide member <NUM> is moved along the axis Lc against an elastic force of the coil spring <NUM>.

<FIG> is a cross-sectional view taken along a line VII-VII shown in <FIG>.

A radius Rs of the inner peripheral surface of each of the divided movable pieces 47A and 47B is smaller than a radius R0 of the outer peripheral surface of the gripped dental treatment tool <NUM> (Rs < R0). In this case, when the divided movable pieces 47A and 47B grip the dental treatment tool <NUM>, each of circumferential end portions <NUM> of the inner peripheral surface of each of the divided movable pieces 47A and 47B comes into line contact with the outer peripheral surface of the dental treatment tool <NUM>. As a result, the circumferential end portions <NUM> are easy to elastically bite into the dental treatment tool <NUM>, and reliable chucking of the dental treatment tool <NUM> may be realized.

Next, a chucking operation of the dental treatment tool <NUM> performed by the chuck mechanism having the above configuration will be described.

<FIG> are views stepwisely illustrating a process of performing the chucking operation by inserting a dental treatment tool into the chuck mechanism <NUM>. Although illustration is simplified, rearward movement of the restriction ring <NUM> in the insertion direction is restricted by the stepped portion <NUM> provided on the inner peripheral surface of the sleeve <NUM> shown in <FIG>.

When the push button <NUM> is further pressed down, an end portion of the pusher <NUM> in the direction opposite to the insertion direction comes into contact with the divided movable pieces 47A and 47B, so that the divided movable pieces 47A and 47B are moved in the direction opposite to the insertion direction. As a result, since the fourth tapered surface <NUM> slides on the third tapered surface <NUM>, the divided movable pieces 47A and 47B are moved outward in the radial direction. An operation of pressing the push button <NUM> down is limited to a position where the groove wall <NUM> of each of the divided movable pieces 47A and 47B comes into contact with the restriction ring <NUM>.

In this state, the dental treatment tool <NUM> is inserted into the sleeve <NUM> in a direction of an arrow K, and as shown in <FIG>, a tip end of the dental treatment tool <NUM> is inserted into the inner peripheral surfaces of the divided movable pieces 47A and 47B. At this time, the tip end of the dental treatment tool <NUM> comes into contact with the chamfered portion <NUM> formed at the end portion of the inner peripheral surface of each of the divided movable pieces 47A and 47B, and the dental treatment tool <NUM> is inserted while the divided movable pieces 47A and 47B are pushed so as to be moved outward. Radial positions of the divided movable pieces 47A and 47B are adjusted by sliding of the first tapered surface <NUM> and the second tapered surface <NUM> and sliding of the fourth tapered surface <NUM> on the third tapered surface <NUM> which are associated with an insertion operation of the dental treatment tool <NUM>.

That is, when an outer peripheral surface of the tip end of the dental treatment tool <NUM> is inserted into inner peripheral sides of the divided movable pieces 47A and 47B, the divided movable pieces 47A and 47B are disposed at the radial positions corresponding to an outer diameter of the dental treatment tool <NUM>. Since the divided movable pieces 47A and 47B are rotatably disposed in the sleeve <NUM>, it becomes easy to match an outer peripheral surface of the dental treatment tool <NUM> and inner circumferential surfaces of the divided movable pieces 47A and 48B, and catching is less likely to occur when the dental treatment tool <NUM> is inserted.

In a case where the dental treatment tool <NUM> is inserted to a predetermined position in the sleeve <NUM>, an operator release a pushing of the push button. As shown in <FIG>, by a biasing force F1 from the coil spring <NUM>, the cylindrical slide member <NUM> is pushed and moved forward in the insertion direction of the dental treatment tool <NUM>. Then, a wedge effect between the first tapered surface <NUM> and the second tapered surface <NUM>, and a wedge effect between the third tapered surface <NUM> and the fourth tapered surface <NUM> are generated. By the wedge effect, clamping force Fc is generated and applied to the dental treatment tool <NUM>, and the dental treatment tool <NUM> is chucked inside the sleeve <NUM> by the clamping force Fc.

Next, an operation of releasing chucking will be described.

<FIG> are views stepwisely illustrating the operation of releasing the chucking of the dental treatment tool inserted into the chuck mechanism <NUM>.

From a chucked state of the dental treatment tool <NUM> shown in <FIG>, as shown in <FIG>, the pusher <NUM> is moved in the direction opposite to the insertion direction of the dental treatment tool <NUM> by pressing the push button <NUM> down. Then, as described above, the pusher <NUM> and the cylindrical slide member <NUM> are moved in the direction opposite to the insertion direction against the biasing force of the coil spring <NUM>, so that the divided movable pieces 47A and 47B are separated from the cylindrical slide member <NUM>.

When the push button <NUM> is further pressed down, as shown in <FIG>, the divided movable pieces 47A and 47B are moved in the direction opposite to the insertion direction, so that the divided movable pieces 47A and 47B are moved outward in the radial direction by sliding of the fourth tapered surface <NUM> on the third tapered surface <NUM>.

When the divided movable pieces 47A and 47B are moved outward in the radial direction as described above, the chucking of the dental treatment tool <NUM> is released and the dental treatment tool <NUM> may be extracted as shown in <FIG>.

That is, the outer peripheral surface of each of the divided movable pieces 47A and 47B and the inner peripheral surface of the cylindrical slide member <NUM> come into contact with each other via tapered fitting portions each having a gradient in the axial direction, and the divided movable pieces 47A and 47B are moved in the radial direction by relative movement between each of the divided movable pieces 47A and 47B and the cylindrical slide member <NUM> in the axial direction, so that fixation of the dental treatment tool <NUM> and release of the fixation are performed.

When the dental handpiece is used, vibration and an axial force from the dental treatment tool propagate to the chuck mechanism. Even in such a case, the chuck mechanism <NUM> having the configuration may maintain reliable chucking without loosening the chucking of the dental treatment tool <NUM>.

<FIG> are views stepwisely illustrating an operation of the chuck mechanism when an external force is applied to the chuck mechanism <NUM>.

When an external force Fv is applied to the dental treatment tool <NUM> as shown in <FIG> from a chucked state of the dental treatment tool <NUM> shown in <FIG>, the dental treatment tool <NUM> is pushed into the sleeve <NUM> forward in the insertion direction, and a surface pressure between the third tapered surface <NUM> of the cylindrical fixing member <NUM> and the fourth tapered surface <NUM> of each of the divided movable pieces 47A and 47B increases. As a result, the clamping force Fc applied to the dental treatment tool <NUM> by each of the divided movable pieces 47A and 47B increases, and the dental treatment tool <NUM> is chucked more firmly. At this time, the cylindrical slide member <NUM> and each of the divided movable pieces 47A and 47B are moved together while being in contact with each other by the coil spring <NUM>.

As shown in <FIG>, when the external force Fv further increases, the dental treatment tool <NUM> is moved forward in the insertion direction, and the groove wall <NUM> of each of the divided movable pieces 47A and 47B comes into contact with the restriction ring <NUM>, so that further axial movement is restricted.

As described above, even when the vibration and the axial force act on the dental treatment tool <NUM>, the chuck mechanism <NUM> always continues to chuck the dental treatment tool <NUM>, and the chucking is not loosened.

<FIG> is a schematic cross-sectional view showing a state where the dental treatment tool <NUM> is held between the divided movable pieces 47A and 47B.

The clamping force Fc (see <FIG> and <FIG>) due to tapered fitting described above is converted into a normal force Fn for chucking the dental treatment tool <NUM> via the divided movable piece 47A. As a central angle θ formed by connecting the pair of circumferential end portions <NUM> of each of the divided movable pieces 47A and 47B with a center O of the dental treatment tool <NUM> increases, the normal force Fn increases. When a radius of the inner peripheral surface of each of the divided movable pieces 47A and 47B is set as Rs and a radius of the outer peripheral surface of the dental treatment tool <NUM> is set as R0, if Rs is greater than or equal to R0, the normal force Fn at the circumferential end portion <NUM> is almost zero, and a chucking force (biting) of the dental treatment tool <NUM> is reduced. Therefore, the radius Rs of the inner peripheral surface of each of the divided movable pieces 47A and 47B that grip the dental treatment tool <NUM> is preferably smaller than the radius R0 of the outer peripheral surface of the dental treatment tool <NUM>.

When a circumferential length of each of the divided movable pieces 47A and 47B is extended to be close to a half of a perimeter of a circle (a position of the divided movable piece 47A indicated by a dotted line in <FIG>), the normal force Fn that contributes to the chucking increases, but the divided movable pieces 47A and 47B approach each other and interfere with the push pieces <NUM> (see <FIG>). If interference occurs, the clamping force Fc is a force to sandwich the push piece <NUM>, and the dental treatment tool <NUM> may not be chucked. Since positions of the divided movable pieces 47A and 47B at the time of chucking tend to change greatly depending on a magnitude of the outer diameter of the dental treatment tool <NUM>, a range of the outer diameter of the dental treatment tool <NUM> is limited.

Therefore, it is preferable that the divided movable pieces 47A and 47B are formed to have the circumferential length that allows a circumferential length of at least one sixth or more, preferably one fourth or more, and more preferably one third or more of an outer periphery of the dental treatment tool <NUM> to be exposed. That is, the central angle θ formed by connecting the pair of circumferential end portions <NUM> of each of the divided movable pieces 47A and 47B with a center O of the dental treatment tool <NUM> is preferably <NUM> degrees or less, more preferably <NUM> degrees or less, and further preferably <NUM> degrees or less. By setting each of the divided movable pieces 47A and 47B within the above range, it is possible to expand the range of the outer diameter of the dental treatment tool <NUM> that may be chucked.

Tapered fitting of each of the divided movable pieces 47A and 47B with the cylindrical slide member <NUM> and the cylindrical fixing member <NUM> needs to be set to a taper angle (an angle formed by an axis of the sleeve <NUM> and a tapered surface) that allows reliable chucking and smooth chucking release. In order to generate a sufficient chucking force while keeping a pressing-down stroke of the push button <NUM> at a very small amount of <NUM> or less from the viewpoint of operability, the taper angle is preferably <NUM> degrees or more, more preferably <NUM> degrees or more, and further preferably <NUM> degrees or more. For the same reason, the taper angle is preferably <NUM> degrees or less, more preferably <NUM> degrees or less, and further preferably <NUM> degrees or less.

<FIG> are views each illustrating a case where a taper angle of the first tapered surface <NUM> and the second tapered surface <NUM> is different from a taper angle of the third tapered surface <NUM> and the fourth tapered surface <NUM>.

Each of the divided movable pieces 47A and 47B has the symmetrical shape in which the plane passing through the axial center and perpendicular to the axial direction is used as the symmetry plane, and a taper angle α1 of the first tapered surface <NUM> and the second tapered surface <NUM> is equal to a taper angle α2 of the third tapered surface <NUM> and the fourth tapered surface <NUM>, but the taper angles are not limited thereto. The taper angles may be different from each other on one side and the other side, in the axial direction, of the plane perpendicular to the axial direction.

As shown in <FIG>, when the taper angle α1 is smaller than the taper angle α2, an inclination of the tapered surface with respect to the axial direction is reduced, and the biasing force F1 from the coil spring <NUM> (<FIG>) may be converted into a larger normal force Fn1. Since a clamping force Fc1 is a component of a force of Fn1 in a direction perpendicular to a rotation axis, the clamping force Fc1 may also be increased.

As shown in <FIG>, when the taper angle α1 is larger than the taper angle α2, an inclination of the tapered surface with respect to the axial direction increases, and the normal force Fn1 is reduced. Therefore, a frictional force generated on the tapered surface may be reduced, and occurrence of biting may be prevented.

Although the divided movable pieces 47A and 47B have a configuration in which dividing into two parts in the circumferential direction is performed, the number of divisions is not limited thereto. For example, dividing into three parts or four parts in the circumferential direction may be performed. However, since a chucking force generated on one divided movable piece due to tapered fitting is reduced as the number of divisions increases, it is preferable to reduce the number of divisions when a radial force due to the tapered fitting is small.

According to the chuck mechanism <NUM> described above, the divided movable pieces 47A and 47B are formed into a two-piece structure and each provided with tapered surfaces, so that a wedge effect may be produced, and a small force in a direction of the rotation axis generated by the coil spring <NUM> may be converted into a large force in the radial direction. By providing the tapered surfaces at both ends of each of the divided movable pieces 47A and 47B, even when a force in the insertion direction or the direction opposite to the insertion direction (extraction direction) is applied to the dental treatment tool <NUM>, the outer peripheral surface of the dental treatment tool <NUM> are not separated from the divided movable pieces 47A and 47B, and the dental treatment tool <NUM> does not drop out carelessly or is not excessively inserted.

Each of the divided movable pieces 47A and 47B is provided with the tapered surfaces at two locations, so that an effect of converting a direction of a force by a taper may be doubled, and a sufficient radial force may be obtained even when the taper angle increases. Biting that causes attachment and detachment failures of the dental treatment tool <NUM> is less likely to occur. Furthermore, since the dental treatment tool <NUM> is chucked while the outer peripheral surface of the dental treatment tool <NUM> is in line contact with the inner peripheral surface of each of the divided movable pieces 47A and 47B, a region that contributes to the chucking is widened. As a result, it is possible to obtain a configuration that is resistant to wear and has high durability. In the chuck mechanism <NUM>, a member requiring an elastic force and a member requiring rigidity are separated from each other, so that a material having characteristics required for each member may be freely selected, and a degree of freedom in design may be improved.

Sliding members (the divided movable pieces 47A and 47B, the cylindrical slide member <NUM>, and the cylindrical fixing member <NUM>) that each slide on the tapered surface are formed separately from the coil spring <NUM> serving as the elastic biasing member. Therefore, as compared with a case where the sliding members also function as an elastic biasing member, the sliding members may be formed of a material having a low spring property and higher hardness. As a result, it is possible to further improve wear resistance of the divided movable pieces 47A and 47B, the cylindrical slide member <NUM>, and the cylindrical fixing member <NUM>.

In the tapered fitting described above, each of the divided movable pieces 47A and 47B, the cylindrical slide member <NUM>, and the cylindrical fixing member <NUM> is provided with the tapered surface, but only one of the tapered surfaces that are fitted together may be formed as the tapered surface. When such an one-side taper is used, a structure of the chuck mechanism <NUM> may be simplified.

<FIG> is a schematic cross-sectional view showing the divided movable pieces 47A and 47B that each include the second tapered surface <NUM> on the outer peripheral surface, and the cylindrical slide member <NUM> that includes no first tapered surface on the inner peripheral surface.

As shown in <FIG>, the cylindrical slide member <NUM> may not be provided with the first tapered surface, and an end portion 45a of the inner peripheral surface of the cylindrical slide member <NUM> may slide on the second tapered surface <NUM>. Similarly, the third tapered surface <NUM> may not be provided on the inner peripheral surface of the cylindrical fixing member <NUM> shown in <FIG>, and an end portion of the inner peripheral surface of the cylindrical fixing member <NUM> may slide on the fourth tapered surface <NUM> of each of the divided movable pieces 47A and 47B. Even in such a case, the chucking operation described above may be performed.

<FIG> is a schematic cross-sectional view showing the divided movable pieces 47A and 47B that each include no second tapered surface <NUM> on the outer peripheral surface, and the cylindrical slide member <NUM> that includes the first tapered surface on the inner peripheral surface.

As shown in <FIG>, each of the divided movable pieces 47A and 47B may not be provided with the second tapered surface, and one end portion 47a of the outer peripheral surface of each of the divided movable pieces 47A and 47B may slide on the first tapered surface <NUM> of the cylindrical slide member <NUM>. Similarly, each of the divided movable pieces 47A and 47B may not be provided with the fourth tapered surface, and the other end portion 47b of the outer peripheral surface of each of the divided movable pieces 47A and 47B may slide on the third tapered surface <NUM> on the inner peripheral surface of the cylindrical fixing member <NUM> shown in <FIG>. Even in such a case, the chucking operation described above may be performed.

Furthermore, the above configurations may also be appropriately combined, for example, by not providing the tapered surface on one side, in the axial direction, of each of the divided movable pieces 47A and 47B, and providing the tapered surface only on the other side in the axial direction. The above configurations may be similarly applied to each modification to be described below.

<FIG> is a partial cross-sectional view of a chuck mechanism 43A according to a first modification including the cylindrical fixing member <NUM> that is divided into two parts. The cylindrical fixing member <NUM> of the chuck mechanism 43A is divided, along the axial direction, into a tapered cylindrical member 57A in a region including the third tapered surface <NUM>, and a remaining cylindrical member 57B in a region excluding the tapered cylindrical member 57A.

The third tapered surface <NUM> is formed on the inner peripheral surface of the cylindrical fixing member <NUM>, and the third tapered surface <NUM> performs tapered fitting with the fourth tapered surface <NUM> and is thus required to have high machining accuracy and high wear resistance. However, for the region other than the third tapered surface <NUM>, such conditions are often not required. Therefore, it is preferable to, as shown in <FIG>, divide the cylindrical fixing member <NUM> into the region including the third tapered surface <NUM> for which particularly high machining accuracy and wear resistance are required, and the other region. In this case, for example, the tapered cylindrical member 57A may be formed by machining, with high accuracy, a material having high wear resistance, and the remaining cylindrical member 57B may be formed using a material that is relatively low in cost and good in machinability. That is, the cylindrical fixing member <NUM> may be formed with little waste so that necessary performance may be sufficiently exhibited while reducing material cost. Since an axial length of the tapered cylindrical member 57A is shortened, machinability thereof is improved.

<FIG> is a cross-sectional view showing a chuck mechanism 43B according to a second modification that includes divided movable pieces 48A and 48B whose axial length is extended.

A length from the recessed groove <NUM> to the second tapered surface <NUM> of each of the divided movable pieces 48A and 48B of the chuck mechanism 43B is extended. According to the configuration, when an inclination of the second tapered surface <NUM> is set to be small, a space for forming the tapered surface is easily ensured. As a result, it is possible to obtain the configuration in which a contact area between the first tapered surface <NUM> and the second tapered surface <NUM> may be increased so as to reduce a surface pressure and reduce wear. Similarly, a contact area may be increased by extending a length from the recessed groove <NUM> to the fourth tapered surface <NUM>.

<FIG> is a cross-sectional view showing a chuck mechanism 43C according to a third modification in which each of protruding portions is formed integrally with a respective one of divided movable pieces 49A and 49B.

Each of the divided movable pieces 49A and 49B of the chuck mechanism 43C is formed, between the second tapered surface <NUM> and the fourth tapered surface <NUM>, with a protruding portion <NUM> which is formed along the circumferential direction and protrudes outward in the radial direction. The protruding portion <NUM> may come into contact with one of end portions of the cylindrical slide member <NUM> and the cylindrical fixing member <NUM> facing each other. The sleeve <NUM> is formed with an annular groove portion <NUM> that prevents interference when the divided movable pieces 49A and 49B each including the protruding portion <NUM> are moved outward in the radial direction.

According to the configuration, a structure may be simplified by omitting the restriction ring <NUM> (<FIG>) described above, and movement of the divided movable pieces 49A and 49B in the axial direction may be restricted.

The configuration of each of chuck mechanisms described above may also be further simplified.

<FIG> is a schematic cross-sectional view showing a simplified configuration of a chuck mechanism 43D according to a fourth modification.

In the chuck mechanism 43D, axial movement of divided movable pieces 50A and 50B each including the second tapered surface <NUM> is restricted by a protruding portion <NUM> that protrudes inward from the inner peripheral surface of the sleeve <NUM> in the radial direction. Other configurations may be the same as those of the chuck mechanisms <NUM>, 43A, and 43B described above.

Each of the divided movable pieces 50A and 50B includes, on one end side in the axial direction, a tapered surface (second tapered surface <NUM>) that is in sliding contact with the first tapered surface <NUM> of the cylindrical slide member <NUM>, and includes, on the other end side in the axial direction, an end surface <NUM> that is in contact with the protruding portion <NUM>. That is, the fourth tapered surface <NUM> described above is not provided.

The protruding portion <NUM> may be formed on the inner peripheral surface of the sleeve <NUM> continuously in the circumferential direction, or may be a plurality of protruding portions obtained by dividing in the circumferential direction. The protruding portion <NUM> only needs to be in contact with the end surface <NUM> of each of the divided movable pieces 50A and 50B, and functions as the stopper unit <NUM> that restricts the axial movement of the divided movable pieces 50A and 50B.

According to the chuck mechanism 43D, reliable chucking of the dental treatment tool <NUM> may be performed by tapered fitting of the first tapered surface <NUM> with the second tapered surface <NUM>. Moreover, since a member that requires flexible elasticity such as the coil spring <NUM>, and members that perform tapered fitting with each other and each have excellent wear resistance and high rigidity are separately formed, characteristics required for each member may be easily selected.

<FIG> is a schematic cross-sectional view showing another simplified configuration of a chuck mechanism 43E according to a fifth modification.

The chuck mechanism 43E includes divided movable pieces 52A and 52B that are each provided with a tapered surface only on one side in the axial direction, and axial movement of the divided movable pieces 52A and 52B is restricted by the restriction ring <NUM>. An end portion of the cylindrical fixing member <NUM> on a restriction ring <NUM> side does not include a tapered surface (third tapered surface <NUM>), and an end surface of the cylindrical fixing member <NUM> abuts against the restriction ring <NUM>. Other configurations are the same as those of the chuck mechanism <NUM> shown in <FIG>.

According to the configuration, similarly to the chuck mechanism 43D according to the fourth modification, the reliable chucking may be performed by the tapered fitting of the first tapered surface <NUM> with the second tapered surface <NUM>, and machining of the sleeve <NUM> may be simplified.

Claim 1:
A dental handpiece (<NUM>) configured to rotatably drive a dental treatment tool (<NUM>) mounted in a chuck mechanism, the dental hand piece comprising:
the chuck mechanism in which the dental treatment tool is mounted so as to be attachable and detachable,
wherein the chuck mechanism includes:
a hollow cylindrical sleeve (<NUM>) into which the dental treatment tool (<NUM>) is inserted so as to be rotatably supported;
a cylindrical slide member (<NUM>) housed in the sleeve so as to be movable in an axial direction of the sleeve;
a plurality of divided movable pieces (47A, 47B) disposed in the sleeve at different circumferential positions to each other, each of the plurality of divided movable pieces including an outer peripheral surface that comes into contact with an inner peripheral surface of the cylindrical slide member, and an inner peripheral surface that comes into contact with an outer peripheral surface of the dental treatment tool inserted into the sleeve, and the dental treatment tool being held between the plurality of divided movable pieces;
an elastic biasing member (<NUM>) configured to bias the cylindrical slide member forward in an insertion direction of the dental treatment tool; and
a stopper unit (<NUM>) configured to restrict forward axial movement of the plurality of divided movable pieces in the insertion direction, at least a part of the stopper unit being partially fixed to the sleeve, and
wherein the outer peripheral surface of each of the plurality of divided movable pieces (47A, 47B) and the inner peripheral surface of the cylindrical slide member (<NUM>) contact with each other via a tapered fitting portion (<NUM>, <NUM>) having a gradient in the axial direction, the tapered fitting portion being provided on at least one of the outer peripheral surface of the plurality of divided movable pieces (47A, 47B) and the inner peripheral surface of the cylindrical slide member (<NUM>),
wherein the divided movable pieces (47A, 47B) are moved in a radial direction by relative movement between each of the divided movable pieces (47A, 47B) and the cylindrical slide member (<NUM>) in the axial direction, so that fixation of the dental treatment tool (<NUM>) and release of the fixation are performed, and
characterized in that
the plurality of divided movable pieces (47A, 47B) are disposed in the sleeve (<NUM>) so as to be rotatable with respect to the sleeve about an axis of the sleeve.