Patent Description:
Known examples of such a clamping apparatus include an apparatus described in Patent Literature <NUM> specified below. The known apparatus is structured as follows.

The clamping apparatus described in Patent Literature <NUM> includes: locking members insertable into a hole of a workpiece; a clamp rod configured to make wedge engagement from above with the locking members; and an advance spring pushing the locking members upward (toward an unclamping side) with a predetermined amount of force. A peripheral wall of the hole of the workpiece is pressed from above by protrusions of the locking members, and thereby the workpiece is clamped. <CIT> discloses an apparatus according to the preambles of claims <NUM>, <NUM> and <NUM>.

The above-described known apparatus has the following disadvantages.

Depending on the structures of elements of the clamping apparatus, outer peripheral surfaces of base portions of the locking members may, due to plastic deformation, bite into or come into strong and close contact with an inner peripheral surface of the hole of the workpiece when the locking members are in a diameter-expanded position, that is, when the apparatus is in a clamping state.

If the clamp rod in the above situation is moved upward (toward the unclamping side), the locking members ascend while holding the workpiece, and this may unintentionally change the position of the workpiece.

An object of the present invention is to provide a clamping apparatus capable of reducing or minimizing the possibility that a to-be-clamped object such as a workpiece is lifted up in unclamping action.

In a first aspect the invention provides a clamping apparatus as claimed in claim <NUM>.

Even if an outer peripheral surface of the locking member bites into or is in strong and close contact with an inner peripheral surface of the hole of the object, it is possible to reduce or minimize the possibility that the locking member moves toward the leading end side while holding the object, because the locking member moves toward the leading end side after moving radially inward, when the clamp rod is driven for unclamping action.

In this arrangement, the resistance giving mechanism can be easily produced.

In a further aspect the invention provides a clamping apparatus as claimed in claim <NUM>.

In a yet further aspect the invention provides a clamping apparatus as claimed in claim <NUM>.

Furthermore, in the clamping apparatus of the above aspect of the invention, it is preferable that the engagement maintaining mechanism <NUM> includes: a rod-side engagement groove 24a or rod-side engagement portion provided on the wedge surface <NUM> of the clamp rod <NUM>; and a locking-member-side engagement portion 25a configured to be fitted in the rod-side engagement groove 24a or a locking-member-side engagement groove in which the rod-side engagement portion is configured to be fitted, the engagement portion 25a or the engagement groove being provided on the locking member <NUM>.

This arrangement makes it possible to easily produce the engagement maintaining mechanism which operates stably.

Furthermore, it is preferable that the clamping apparatus of the above aspect of the invention further includes a relative movement restriction mechanism <NUM> configured to restrict radially outward movement of the locking member <NUM> relative to the clamp rod <NUM> within a predetermined range when the clamp rod <NUM> is driven toward the base end side for clamping action.

This arrangement reduces or minimizes the possibility that the outer peripheral surface of the locking member bites into or comes into strong and close contact with the inner peripheral surface of the hole of the object.

Furthermore, in the clamping apparatus of the above aspect of the invention, it is preferable that the relative movement restriction mechanism <NUM> is an annular protrusion <NUM> provided at a leading-end-side end portion of the housing <NUM> and protruding radially inward, and a hole in the annular protrusion <NUM> has a diameter equal to or smaller than a diameter of the hole Wa of the to-be-clamped object W.

In this arrangement, the relative movement restriction mechanism can be easily produced.

Furthermore, in the clamping apparatus of the above aspect of the invention, it is preferable that the support member <NUM> includes: a tubular portion <NUM> in which the clamp rod <NUM> is inserted so as to be movable in the axial direction; a peripheral wall portion <NUM> provided on the leading end side relative to the tubular portion <NUM>, the peripheral wall portion <NUM> having a guide hole 21a in which the locking member <NUM> is inserted so as to be radially movable; and a tapered top wall portion <NUM> provided on the leading end side relative to the peripheral wall portion <NUM>.

Due to this arrangement of the support member, it is possible to prevent a peripheral wall of the hole of the object from colliding with the locking member when the object is placed. Furthermore, this makes the operation of the locking member more stable in clamping and unclamping action.

According to embodiments of the clamping apparatus it is possible to reduce or minimize the possibility that a to-be-clamped object such as a workpiece is lifted up in unclamping action.

<FIG> show a first embodiment of the present invention. A clamping apparatus of this embodiment is used to fasten a workpiece W functioning as a to-be-clamped object. The workpiece W is, for example, a steel plate used as material for automotive panels with a thickness of approximately <NUM> to <NUM>, for example. The workpiece W has a hole Wa.

The structure of the clamping apparatus of the first embodiment of the present invention will be described with reference to <FIG>.

A housing <NUM> is attached to a stationary stand T such as a table. The housing <NUM> includes: a lower housing <NUM>; a lid member <NUM> which hermetically closes an opening of a lower end portion of a cylinder hole 2a provided in the lower housing <NUM>; and a tubular upper housing <NUM> fixed to a top surface of the lower housing <NUM> with a bolt <NUM>. The lower housing <NUM> has the cylinder hole 2a and a small-diameter hole 2b, which are provided from bottom to top in this order.

A piston <NUM> is hermetically inserted in the cylinder hole 2a. A clamp rod <NUM> protruding upward from the piston <NUM> is hermetically inserted in the small-diameter hole 2b. Compressed air is supplied to and discharged from a clamp chamber <NUM> provided above the piston <NUM> via an air supply and discharge port <NUM>. Compressed air is also supplied to and discharged from an unclamp chamber <NUM> provided below the piston <NUM> via another air supply and discharge port <NUM>. The piston <NUM>, the clamp chamber <NUM>, and the unclamp chamber <NUM> constitute a driving means <NUM> configured to drive the clamp rod <NUM> downward for clamping action and to drive the clamp rod <NUM> upward for unclamping action. Although the clamp rod <NUM> and the piston <NUM> are unitary with each other in this embodiment, these may be separately formed and then fixed into one piece. Springs <NUM> and <NUM> functioning as a biasing means are housed in the clamp chamber <NUM>. The springs <NUM> and <NUM> bias the clamp rod <NUM> downward via the piston <NUM>.

A seat portion <NUM> configured to receive the workpiece W is provided on an upper end surface of the upper housing <NUM>. A detection passage <NUM> extending in an up-down direction is provided in a side wall of the upper housing <NUM>. An upper end of the detection passage <NUM> opens onto the seat portion <NUM>, while a lower end of the detection passage <NUM> is communicatively connected to an air supply port <NUM>.

A support member <NUM> is inserted in an upper-side portion of the upper housing <NUM> so as to be movable in its axial direction. The support member <NUM> includes: a tubular portion <NUM>; a peripheral wall portion <NUM> having a diameter smaller than that of the tubular portion <NUM>; and a top wall portion <NUM> tapered down toward its leading end. These portions are provided from bottom to top in this order. The peripheral wall portion <NUM> and the top wall portion <NUM> protrude upward relative to an upper end of the upper housing <NUM> and they are configured to be insertable into the hole Wa of the workpiece W.

The peripheral wall portion <NUM> has three guide holes 21a provided at intervals of <NUM> degrees in its circumferential direction. A locking member <NUM> is inserted in each of the guide holes 21a so as to be radially movable. Each locking member <NUM> has a proximal end portion <NUM>, a base portion <NUM>, and a protruding portion <NUM>, which are provided from bottom to top in this order. The proximal end portion <NUM> is a portion which is supported from below by the tubular portion <NUM> of the support member <NUM>. An outer peripheral surface of the protruding portion <NUM> is located radially outward relative to an outer peripheral surface 28a of the base portion <NUM>. It should be noted that only one of the locking members <NUM> is shown in <FIG> and other figures.

An annular protrusion <NUM> protruding radially inward is provided at an upper end portion of the upper housing <NUM>. The protrusion <NUM> constitutes a relative movement restriction mechanism <NUM> configured to restrict radially outward movement of the locking members <NUM> relative to the clamp rod <NUM> within a predetermined range when the clamp rod <NUM> is driven downward for clamping action. The diameter of the hole inside the protrusion <NUM> is designed to be equal to the diameter of the hole Wa of the workpiece W. The diameter of the hole inside the protrusion <NUM> may be smaller than that of the hole Wa of the workpiece W.

The clamp rod <NUM> is inserted in the tubular portion <NUM> and in the peripheral wall portion <NUM> from below so as to be movable in the axial direction. Wedge surfaces <NUM> are provided on an upper portion of the clamp rod <NUM>. Each wedge surface <NUM> is engaged from above with an inclined surface <NUM> of the corresponding one of the locking members <NUM>. The inclined surface <NUM> is provided opposite from the outer peripheral surface 28a. The wedge surfaces <NUM> and the inclined surfaces <NUM> are flat surfaces in this embodiment, and each surface is inclined so that the distance between the surface and the axis of the clamp rod <NUM> decreases downward. In this embodiment, three wedge surfaces <NUM> are provided at intervals of <NUM> degrees in the circumferential direction of the clamp rod <NUM>, in correspondence with the number of the locking members <NUM>.

On each wedge surface <NUM>, there is provided a rod-side engagement groove 24a extending in the up-down direction along the wedge surface <NUM>. On each inclined surface <NUM>, there is provided a locking-member-side engagement portion 25a extending in the up-down direction along the inclined surface <NUM>. Each locking-member-side engagement portion 25a is engaged with the corresponding rod-side engagement groove 24a. The locking-member-side engagement portions 25a and the rod-side engagement grooves 24a constitute an engagement maintaining mechanism <NUM> which allows the wedge surfaces <NUM> of the clamp rod <NUM> to be engaged with the respective inclined surfaces <NUM> of the locking members <NUM> so that the surfaces <NUM> and <NUM> are movable relative to each other.

A tapered surface 7a, tapering down toward a leading end, is provided on an outer periphery of the clamp rod <NUM>.

The support member <NUM> is guided in the up-down direction by a straight-movement guiding mechanism <NUM>. The straight-movement guiding mechanism <NUM> includes: a ball <NUM> attached in an inner peripheral wall of the upper housing <NUM>; and a straight-movement guiding groove <NUM> provided on an outer peripheral surface of the tubular portion <NUM> of the support member <NUM> and extending in the up-down direction. The ball <NUM> is inserted in the straight-movement guiding groove <NUM>.

An annular groove <NUM> is provided on an outer peripheral surface of a lower end portion of the tubular portion <NUM>. A retaining ring <NUM> functioning as a ring-like elastic member is attached in the annular groove <NUM>. The annular groove <NUM> and the retaining ring <NUM> constitute a resistance giving mechanism <NUM> configured to give resistance to the axial movement (movement in the up-down direction) of the support member <NUM>. A portion indicated with the reference numeral 33a is a slit of the retaining ring <NUM>. That is, the retaining ring <NUM> is a so-called C-shaped retaining ring. Instead of the C-shaped retaining ring, a complete-ring-shaped or O-shaped retaining ring may be used as a ring-like elastic member. An annular groove 5a is provided on an inner peripheral surface of the upper housing <NUM>. The retaining ring <NUM> is fitted in the groove 5a in an unclamping state.

The clamping apparatus having the above-described structure operates as follows.

In the unclamping state shown in <FIG>, compressed air in the clamp chamber <NUM> has been discharged, and compressed air has been supplied to the unclamp chamber <NUM>. As a result, the piston <NUM> has moved the clamp rod <NUM> to an upper unclamping position against the biasing forces of the springs <NUM> and <NUM>, and each locking member <NUM> has been retracted radially inward by the engagement maintaining mechanism <NUM>.

In this state, the outer peripheral surface of the protruding portion <NUM> of each locking member <NUM> is located inward of an outer peripheral surface of the peripheral wall portion <NUM> of the support member <NUM>. This prevents a peripheral wall of the hole Wa of the workpiece W from colliding with the locking members <NUM>. As the workpiece W is lowered in this unclamping state, the hole Wa of the workpiece W is located around the peripheral wall portion <NUM> of the support member <NUM> and around the locking members <NUM>, with a predetermined gap.

To cause the apparatus to transition from the unclamping state shown in <FIG> to a clamping state shown in <FIG>, compressed air in the unclamp chamber <NUM> is discharged and compressed air is supplied to the clamp chamber <NUM>, to lower the piston <NUM>.

As a result, the clamp rod <NUM> descends first, as shown in <FIG>. Due to the elastic restoring force of the retaining ring <NUM> of the resistance giving mechanism <NUM>, the support member <NUM> and the locking members <NUM> are held at their respective positions in the unclamping state shown in <FIG>, or these members are slightly lowered.

As the clamp rod <NUM> descends, the wedge surfaces <NUM> push the locking members <NUM> radially outward to bring the outer peripheral surfaces 28a of the base portions <NUM> of the locking members <NUM> into contact with: an inner peripheral surface of the hole Wa of the workpiece W; and an inner peripheral surface of the protrusion <NUM> provided at the upper end portion of the upper housing <NUM>. As the outer peripheral surfaces 28a of the base portions <NUM> of the locking members <NUM> are thus brought into contact with the inner peripheral surface of the hole Wa of the workpiece W, the workpiece W is positioned with respect to a horizontal direction. Meanwhile, the protruding portions <NUM> of the locking members <NUM> face the peripheral wall of the hole Wa from above.

After the locking members <NUM> come into contact with the inner peripheral surface of the protrusion <NUM>, the locking members <NUM> cannot move radially outward anymore. Because of this, the wedge surfaces <NUM> of the clamp rod <NUM> push the locking members <NUM> and the support member <NUM> downward, with the result that the locking members <NUM> and the support member <NUM>, as well as the clamp rod <NUM>, descend together against the elastic restoring force of the retaining ring <NUM>. Because the diameter of the hole in the protrusion <NUM> is designed to be equal to the diameter of the hole Wa of the workpiece W, the locking members <NUM> do not have a great impact onto the inner peripheral surface of the hole Wa of the workpiece W. Thus, damage to the inner peripheral surface of the hole Wa can be reduced or minimized.

Thereafter, as shown in <FIG>, under surfaces of the protruding portions <NUM> of the locking members <NUM> reach the level of a top surface of the peripheral wall of the hole Wa of the workpiece W, and the peripheral wall of the hole Wa is pressed onto the seat portion <NUM> of the upper housing <NUM> by the protruding portions <NUM> of the locking members <NUM>. The workpiece W is thus clamped. The biasing forces of the springs <NUM> and <NUM> housed in the clamp chamber <NUM> enhance the capability of holding the workpiece W.

In the clamping state shown in <FIG>, the detection passage <NUM> is closed by an under surface of the workpiece W. Due to this, the pressure of pressurized air supplied to the detection passage <NUM> to detect the workpiece becomes higher than a set pressure. Such an increase in pressure is detected by a pressure switch or the like, to confirm that the workpiece W has been clamped.

To cause the apparatus to transition from the clamping state shown in <FIG> to the unclamping state shown in <FIG>, compressed air in the clamp chamber <NUM> is discharged and compressed air is supplied to the unclamp chamber <NUM>, to raise the piston <NUM>.

As a result, the clamp rod <NUM> ascends first, as shown in <FIG>. The support member <NUM> and the locking members <NUM> are held at their respective positions in the clamping state shown in <FIG> (at their respective lowered positions) due to the elastic restoring force of the retaining ring <NUM> of the resistance giving mechanism <NUM>.

As the clamp rod <NUM> ascends, the locking members <NUM> are retracted radially inward with the movement of the wedge surfaces <NUM>, and therefore the protruding portions <NUM> of the locking members <NUM> are moved radially inward away from the peripheral wall of the hole Wa of the workpiece W. This is because: the upward movement of the locking members <NUM> is restricted by the support member <NUM> (i.e., the upward movement of the locking members <NUM> is restricted by upper end surfaces of the respective guide holes 21a); and the wedge surfaces <NUM> of the clamp rod <NUM> are respectively engaged with the locking members <NUM> by the engagement maintaining mechanism <NUM> so as to be relatively movable.

As the clamp rod <NUM> ascends further, the tapered surface 7a provided on the outer periphery of the clamp rod <NUM> comes to abut an inner peripheral edge portion of an upper end portion of the tubular portion <NUM> of the support member <NUM>. Then the locking members <NUM> and the support member <NUM>, as well as the clamp rod <NUM>, ascend together against the elastic restoring force of the retaining ring <NUM>. In other words, the clamp rod <NUM> moves the locking members <NUM> upward via the support member <NUM>.

Thereafter, an upper end surface of the tubular portion <NUM> comes to abut an inner portion of a ceiling surface of the upper housing <NUM>, which stops the ascent of the clamp rod <NUM>, and the apparatus is into the unclamping state shown in <FIG>.

<FIG> show a second embodiment of the present invention. The following describes a difference between a clamping apparatus of the second embodiment and the clamping apparatus of the first embodiment.

The difference between the second embodiment and the first embodiment is in the structure of the resistance giving mechanism <NUM>. The resistance giving mechanism <NUM> of the second embodiment is structured as follows.

A lateral hole <NUM> is bored in a side wall of the upper housing <NUM>, that is, in a side wall of a leading-end-side portion of the housing <NUM>. In the lateral hole <NUM>, a ball <NUM> and a spring <NUM> are attached. The ball <NUM> functions as an engagement member, while the spring <NUM> functions as a biasing means configured to bias the ball <NUM> toward the tubular portion <NUM> of the support member <NUM>. The lateral hole <NUM>, the ball <NUM>, and the spring <NUM> constitute the resistance giving mechanism <NUM>. An annular plate <NUM> is attached to a portion of an outer peripheral surface of the upper housing <NUM>, which is outward of the spring <NUM>. Furthermore, a lateral hole <NUM>, into which a portion of the ball <NUM> is fitted in the unclamping state, is bored in the tubular portion <NUM>. The diameter of the lateral hole <NUM> is smaller than that of the lateral hole <NUM>. Due to this, only a portion of the ball <NUM>, which is smaller than a half thereof, is fitted in the lateral hole <NUM> when the support member <NUM> is at its raised position. The ball <NUM> is always attached in the lateral hole <NUM>, as well as the spring <NUM>.

The clamping apparatus of the second embodiment operates as follows, when the clamping apparatus is driven for the unclamping action from the clamping state shown in <FIG> to the unclamping state shown in <FIG>.

In the clamping apparatus in the above-described clamping state, compressed air in the clamp chamber <NUM> is discharged and compressed air is supplied to the unclamp chamber <NUM>, to raise the piston <NUM>. As a result, the clamp rod <NUM> ascends first, as shown in <FIG>. The support member <NUM> and the locking members <NUM> are held at their respective positions in the clamping state shown in <FIG> (at their respective lowered positions) by the elastic restoring force of the spring <NUM> of the resistance giving mechanism <NUM>.

As the clamp rod <NUM> ascends, the wedge surfaces <NUM> cause the locking members <NUM> to retract radially inward, and the protruding portions <NUM> of the locking members <NUM> are moved radially inward away from the peripheral wall of the hole Wa of the workpiece W.

As the clamp rod <NUM> ascends further, the tapered surface 7a provided on the outer periphery of the clamp rod <NUM> comes to abut the inner peripheral edge portion of the upper end portion of the tubular portion <NUM> of the support member <NUM>. Then the locking members <NUM> and the support member <NUM>, as well as the clamp rod <NUM>, ascend together against the elastic restoring force of the spring <NUM>. Thereafter, the upper end surface of the tubular portion <NUM> comes to abut an inner portion of the ceiling surface of the upper housing <NUM>, which stops the ascent of the clamp rod <NUM>, and the apparatus is into the unclamping state shown in <FIG>.

<FIG> show a third embodiment of the present invention. The following describes a difference between a clamping apparatus of the third embodiment and the clamping apparatus of the first embodiment.

The difference between the third embodiment and the first embodiment is in the structure of the resistance giving mechanism <NUM>. The resistance giving mechanism <NUM> of the third embodiment is structured as follows.

An inclined surface <NUM>, which is inclined relative to the axial direction, is provided on an outer periphery of the tubular portion <NUM> of the support member <NUM>. A wedge member <NUM> engaged with the inclined surface <NUM> from below is attached between the inclined surface <NUM> and the inner peripheral surface of the upper housing <NUM>. A spring <NUM> functioning as a biasing means configured to bias the wedge member <NUM> upward is held close to the outer peripheral surface of the tubular portion <NUM> by a holding means <NUM> constituted by an annular spring receiver <NUM> and a retaining ring <NUM>. The wedge member <NUM>, the spring <NUM>, and the holding means <NUM> constitute the resistance giving mechanism <NUM>. The annular wedge member <NUM> has a slit 43a, and is therefore elastically deformable in the radial direction.

The clamping apparatus of the third embodiment operates as follows in the unclamping action.

Compressed air in the clamp chamber <NUM> is discharged and compressed air is supplied to the unclamp chamber <NUM>, to raise the piston <NUM>. As a result, the clamp rod <NUM> ascends first, as shown in <FIG>. The support member <NUM> and the locking members <NUM> are held at their respective positions in the clamping state shown in <FIG> (at their respective lowered positions) by the wedge member <NUM>, which radially disperses the biasing force of the spring <NUM> of the resistance giving mechanism <NUM>.

As the clamp rod <NUM> ascends further, the tapered surface 7a provided on the outer periphery of the clamp rod <NUM> comes to abut the inner peripheral edge portion of the upper end portion of the tubular portion <NUM> of the support member <NUM>. Then the locking members <NUM> and the support member <NUM>, as well as the clamp rod <NUM>, ascend together against the resistance from the wedge member <NUM>. Thereafter, the upper end surface of the tubular portion <NUM> comes to abut the inner portion of the ceiling surface of the upper housing <NUM>, which stops the ascent of the clamp rod <NUM>, and the apparatus is into the unclamping state shown in <FIG>.

<FIG> and <FIG> show a fourth embodiment of the present invention. The following describes differences between a clamping apparatus of the fourth embodiment and the clamping apparatus of the third embodiment.

The differences between the fourth embodiment and the third embodiment are: in the structure of the support member <NUM>; in the structure of the relative movement restriction mechanism <NUM>; in the structure of the resistance giving mechanism <NUM>; and in the structure of the locking members <NUM>. While the workpiece W (object to be clamped) in each of the first to third embodiments is thin, a workpiece W in the fourth embodiment is thick.

The support member <NUM> of the fourth embodiment is structured as follows.

Differently from that in the first to third embodiments, the support member <NUM> in the fourth embodiment has neither the peripheral wall portion <NUM> nor the top wall portion <NUM>, and is structured only by the tubular portion <NUM>.

The relative movement restriction mechanism <NUM> of the fourth embodiment is structured as follows. A pin <NUM> is attached to the clamp rod <NUM> so as to radially penetrate the clamp rod <NUM>. Elongated holes <NUM>, each elongated in the axial direction (in the up-down direction), are provided in a peripheral wall of the support member <NUM> (of the tubular portion <NUM>). End portions 48a of the pin <NUM> are respectively inserted in the elongated holes <NUM>. The pin <NUM> and the elongated holes <NUM> constitute the relative movement restriction mechanism <NUM>.

The resistance giving mechanism <NUM> of the fourth embodiment is structured as follows.

The biasing means of the resistance giving mechanism <NUM> is constituted by an O ring <NUM> and compressed air, instead of the spring in the third embodiment. Compressed air supplied from the air supply port <NUM> not only flows into the detection passage <NUM>, but also flows upward in the upper housing <NUM>. To be more specific, compressed air supplied from the air supply port <NUM> is also supplied to a cylindrical hollow space of the upper housing <NUM>, through a groove provided between: a bottom surface of a recessed portion at an upper end portion of the lower housing <NUM>; and an under surface of the upper housing <NUM>. Compressed air supplied to the cylindrical hollow space of the upper housing <NUM> pushes the O ring <NUM> upward, functioning as one of elements constituting the biasing means. The O ring <NUM> is attached in a space created between the inner peripheral surface of the upper housing <NUM> and an outer peripheral surface of a lower portion of the tubular portion <NUM>, so as to push the wedge member <NUM> upward. The spring receiver <NUM> of the third embodiment is an O ring receiver in the fourth embodiment. Compressed air does not have to be always supplied into the cylindrical hollow space in the upper housing <NUM> from its bottom portion if the elastic restoring force of the O ring <NUM> is large enough. That is, the biasing means of the resistance giving mechanism <NUM> may be constituted only by the O ring <NUM>. Alternatively, the wedge member <NUM> may be biased upward only by compressed air supplied into the cylindrical hollow space in the upper housing <NUM> from its bottom portion, instead of the above arrangement in which the biasing means is constituted only by the elastic restoring force of the O ring <NUM>.

The locking members <NUM> of the fourth embodiment are structured as follows.

Differently from those in the first to third embodiments, each locking member <NUM> in this embodiment has no protruding portion <NUM>, and is constituted by the proximal end portion <NUM> and the base portion <NUM>. Furthermore, an accommodation groove 28b is provided in the circumferential direction on an outer peripheral wall of the base portion <NUM> of each locking member <NUM>. (It should be noted that <FIG> and <FIG> each shows only one of the three locking members <NUM>. ) A ring-like elastic member 28c is attached in the accommodation grooves 28b of the three locking members <NUM>. The elastic member 28c is made of rubber, resin, or the like. The elastic member 28c biases the three locking members <NUM> toward the axis of the clamp rod <NUM>. The elastic member 28c is provided to firmly hold the locking members <NUM> at a leading end portion of the clamp rod <NUM>.

In this embodiment, the outer peripheral surfaces 28a of the base portions <NUM> are pressed onto the inner peripheral surface of the hole Wa of the workpiece W, to clamp the workpiece W.

The clamping apparatus of the fourth embodiment operates as follows.

To cause the apparatus to transition from the unclamping state shown in <FIG> to the clamping state shown in <FIG>, compressed air in the unclamp chamber <NUM> is discharged and compressed air is supplied to the clamp chamber <NUM>, to lower the piston <NUM>.

As a result, the clamp rod <NUM> descends. Due to this, the wedge surfaces <NUM> of the clamp rod <NUM> push the locking members <NUM> radially outward, and the outer peripheral surfaces 28a of the base portions <NUM> of the locking members <NUM> push the inner peripheral surface of the hole Wa of the workpiece W. The workpiece W is thus clamped. When the clamp rod <NUM> is lowered, the end portions 48a of the pin <NUM> is brought into contact with respective bottom surfaces of the elongated holes <NUM>, and the support member <NUM> and the locking members <NUM> descend slightly. The contact of the end portions 48a of the pin <NUM> with the respective bottom surfaces of the elongated holes <NUM> prevents the locking members <NUM> from moving further radially outward.

As a result, the clamp rod <NUM> ascends first. The support member <NUM> and the locking members <NUM> are held at their respective positions in the clamping state (at their respective lowered positions) by the wedge member <NUM>, which radially disperses the biasing force of the O ring <NUM> of the resistance giving mechanism <NUM>.

As the clamp rod <NUM> ascends, the wedge surfaces <NUM> cause the locking members <NUM> to retract radially inward, and the outer peripheral surfaces 28a of the base portions <NUM> of the locking members <NUM> move radially inward away from the inner peripheral surface of the hole Wa of the workpiece W.

As the clamp rod <NUM> ascends further, a stepped portion 7b of an upper portion of the clamp rod <NUM> comes to abut the inner peripheral edge portion of the upper end portion of the support member <NUM>, or the end portions 48a of the pin <NUM> come to abut respective ceiling surfaces of the elongated holes <NUM>. Then the locking members <NUM> and the support member <NUM>, as well as the clamp rod <NUM>, ascend together against the resistance from the wedge member <NUM>. Thereafter the ascent of the clamp rod <NUM> stops, and the apparatus is into the unclamping state shown in <FIG>.

The above-described embodiments are changeable as follows.

Operating fluid used for the driving means <NUM> may be liquid such as pressurized oil, instead of compressed air. The driving means <NUM> may be of a single-acting type such as a spring-releasing type and a spring-locking type, instead of the double-acting type, which has been described by way of example. Furthermore, the driving means <NUM> may be structured by another actuator such as an electrical actuator, instead of the fluid actuator described by way of example.

The two springs <NUM> and <NUM> are disposed in the clamp chamber <NUM>. The number of springs disposed in the clamp chamber <NUM> may be one. Alternatively, no spring may be disposed in the clamp chamber <NUM>.

The number of locking members <NUM> may be two or four or more, instead of three. Alternatively, an annular collet having one or more slits may be used to act as a locking member.

The engagement maintaining mechanism <NUM> may be arranged as follows: instead of the locking-member-side engagement portion 25a, a locking-member-side engagement groove of a groove-like shape may be provided on the inclined surface <NUM> of each locking member <NUM>; and instead of the rod-side engagement groove 24a, a rod-side engagement portion configured to be fitted in the locking-member-side engagement groove may be provided on each wedge surface <NUM> of the clamp rod <NUM>.

Furthermore, it is possible to arrange the mechanism as follows: the locking-member-side engagement portion 25a and the rod-side engagement groove 24a are not provided; and an annular elastic member is fitted over an upper end portion of the clamp rod <NUM> provided with the wedge surfaces <NUM> and over the locking members <NUM>, to maintain the engagement between the wedge surfaces <NUM> of the clamp rod <NUM> and the respective locking members <NUM>. For example, the following configuration is possible: the accommodation groove 28b is provided on the outer peripheral wall of each base portion <NUM> similarly to the locking members <NUM> of the fourth embodiment shown in <FIG> and <FIG>; and the annular elastic member 28c functioning as the above-mentioned elastic member is fitted in the accommodation grooves 28b, to maintain the engagement between the wedge surfaces <NUM> of the clamp rod <NUM> and the respective locking members <NUM>.

For the resistance giving mechanism <NUM> in the firstembodiment, an elastic member such as an O ring may be used instead of the retaining ring <NUM>.

In the description of the operation at the time of the unclamping action in the first to third embodiments, the tapered surface 7a provided on the outer periphery of the clamp rod <NUM> comes to abut the inner peripheral edge portion of the upper end portion of the tubular portion <NUM> of the support member <NUM>, and consequently the locking members <NUM> and the support member <NUM>, as well as the clamp rod <NUM>, ascend together. Instead of this, the apparatus may be arranged so that: the locking members <NUM> and the support member <NUM>, as well as the clamp rod, <NUM> ascend together by causing an upper end surface of the clamp rod <NUM> to abut an inner wall surface of the top wall portion <NUM> of the support member <NUM> to lift up the support member <NUM>.

Instead of the support member <NUM> of the clamping apparatuses of the first to third embodiments, there may be used the support member <NUM> in the fourth embodiment, which has neither the peripheral wall portion <NUM> nor the top wall portion <NUM> and is structured only by the tubular portion <NUM>.

Instead of the relative movement restriction mechanism <NUM> of the clamping apparatus of each of the first to third embodiments, there may be used the relative movement restriction mechanism <NUM> of the clamping apparatus of the fourth embodiment. Instead of the relative movement restriction mechanism <NUM> of the clamping apparatus of the fourth embodiment, there may be used the relative movement restriction mechanism <NUM> of the clamping apparatus of each of the first to third embodiments.

The resistance giving mechanism <NUM> of the clamping apparatus of the fourth embodiment may be used in the clamping apparatus of the first embodiment. Furthermore, the resistance giving mechanism <NUM> of the clamping apparatus of each of the first to third embodiments may be used in the clamping apparatus of the fourth embodiment.

Instead of the upright or vertical position as illustrated by way of example, the clamping apparatus of the present invention may be placed in an upside-down position, a horizontal position, or a tilted position.

Claim 1:
A clamping apparatus comprising:
a housing (<NUM>);
a locking member (<NUM>) protruding toward a leading end side relative to the housing (<NUM>) and configured to be insertable into a hole (Wa) of a to-be-clamped object (W);
a clamp rod (<NUM>) including a wedge surface (<NUM>) configured to be engaged with the locking member (<NUM>) from the leading end side;
a driving means (<NUM>) configured to drive the clamp rod (<NUM>) toward a base end side for clamping action and to drive the clamp rod (<NUM>) toward the leading end side for unclamping action;
a support member (<NUM>) supporting a base end portion of the locking member (<NUM>) so that the locking member (<NUM>) is radially movable, the support member (<NUM>) being inserted in a leading-end-side portion of the housing (<NUM>) so as to be movable in its axial direction;
a resistance giving mechanism (<NUM>) configured to give resistance to axial movement of the support member (<NUM>); and
an engagement maintaining mechanism (<NUM>) which allows the wedge surface (<NUM>) of the clamp rod (<NUM>) to be engaged with the locking member (<NUM>) so as to be movable relative to each other, wherein
the support member (<NUM>) includes a tubular portion (<NUM>) in which the clamp rod (<NUM>) is inserted so as to be movable in the axial direction, characterised in that
the resistance giving mechanism (<NUM>) includes:
an annular groove (<NUM>) provided on an outer peripheral surface of the tubular portion(<NUM>); and
a ring-like elastic member (<NUM>) attached to the annular groove (<NUM>), wherein
an annular groove (5a) is provided on an inner peripheral surface of a tubular upper housing (<NUM>), and the elastic member (<NUM>) is fitted in the groove (5a) in an unclamping state, and wherein
when the clamp rod (<NUM>) is driven toward the leading end side for unclamping action, the clamp rod (<NUM>) moves the locking member (<NUM>) toward the leading end side via the support member (<NUM>) after the locking member (<NUM>) moves radially inward.