Tweezers and grasping system

The invention proposes tweezers (12) and a grasping system (10) for grasping and assembling at least one component (14) in a timepiece, comprising first and second branches (16, 18), which are joined at a first end (20) of the tweezers (12) and which form a grasping pincer (22) at the second end of the tweezers (12) in order to allow the component (14) to be grasped by the pincer (22), via a manual manipulation of the tweezers (12), characterized in that the first branch (16) includes at least one electrostatic grasping surface (24) provided for grasping, via electrostatic attraction, a component (14) made of conductive or semiconductor material.

This application claims priority from European Patent Application No. 06113848.3, filed May 12, 2006, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention concerns tweezers and a system for grasping and assembling components in a timepiece.

The invention more specifically concerns tweezers for grasping and assembling at least one component in a timepiece, comprising first and second branches which are joined at a first end of the tweezers and which form a grasping pincer at the second end of the tweezers for the purpose of grasping the component via the pincer, by a manual manipulation of the tweezers.

BACKGROUND OF THE INVENTION

During assembly of timepiece components of small dimensions, such as display hands, watchmakers usually use tweezers, which enables them to manipulate the components and position them more precisely in order to create an assembly in a timepiece. Such tweezers are disclosed and shown, for example, in U.S. Pat. No. 3,638,516.

It has become clear that, for certain types of components, the tweezers tend to leave marks on the components. In particular, when the components are made of a semiconductor material such as silicon, the very fragile external surface is marked by scratches from handling by the tweezers, which is damaging to the final aesthetic appearance of the timepiece. Handling by tweezers can even cause breakage of the component.

Grasping the timepiece components by suction has already been proposed, particularly in CH Patent No. 667 839. However, this solution does not solve the problem of marking or breakage of fragile components.

It is an object of the present invention to overcome this problem by proposing a tool which allows easy and precise handling without altering the surface of the components being handled.

SUMMARY OF THE INVENTION

Thus, the invention proposes tweezers of the type previously described, characterized in that the first branch comprises at least one electrostatic grasping surface provided for grasping a component made of conductive or semiconductor material by electrostatic attraction.

The tweezers according to the invention have the advantage of being particularly easy to hold in the hand since they have the shape of a tool that is used daily by watchmakers. Moreover, they can be used in a conventional mode, by means of the pincer, and in an advanced mode, by means of the electrostatic grasping surface, which enables them to be adapted to the requirements of watchmakers.

Preferably, the electrostatic grasping surface is arranged on the side of the outer face of the branch, which facilitates the holding of components by making the electrostatic grasping surface easily accessible while allowing the user to continue to use the conventional pincer for grasping less fragile conventional components.

According to one advantageous embodiment, the electrostatic grasping surface has at least one guide portion, which is provided to force the component to occupy a determined position on the electrostatic grasping surface. This feature enables the component to obtain a stable relative position on the grasping surface, thereby facilitating assembly operations. Moreover, since the tweezers are used for assembling a watch hand on an arbour, the electrostatic grasping surface comprises at least one orifice provided for the passage of the arbour when the hand is positioned thereon, which facilitates the mounting of the hand on its drive arbour in the timepiece.

Advantageously, at least one part of the electrostatic grasping surface belongs to an added element, which is removably secured to the first branch by snap fit. Interchangeable electrostatic grasping surfaces can thus be used as a function of the components to be handled.

According to other features of the invention, the branches are made of an electrically conductive material and the electrostatic grasping surface is made of a synthetic electrically insulating material, whose hardness and surface appearance are provided so as not to alter the surface appearance of the component being grasped.

The first branch comprises an electrode supplied with an electric current by a powering device and an insulating envelope made of dielectric material, which covers the electrode, and the insulating envelope comprises an outer surface that forms the electrostatic grasping surface.

The powering device can be carried by the tweezers or offset in relation to the tweezers.

Preferably, a member controlling the intensity of the electrostatic attractive force produced on the electrostatic grasping surface is arranged on the tweezers, which enables the attraction force to be adapted to the component to be handled, and which allows the component to be released when desired.

The present invention also proposes an electrostatic grasping system comprising tweezers as previously described and including a member, off-set relative to the tweezers, which controls the intensity of the electrostatic attractive force produced on the electrostatic grasping surface. The control member is a pedal, which varies the intensity of the electrostatic attractive force as a function of the pressing force applied to the pedal.

These features enable the grasping system according to the invention to be particularly ergonomic since the user has both hands free for handling the components using the tweezers and for holding the timepiece, while his feet control the electrostatic attractive force.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

In the following description, identical or similar elements bear the same references.

FIG. 1shows a grasping system10according to a first embodiment comprising tweezers12for grasping and assembling at least one component14in a timepiece (not shown), particularly in a wristwatch.

The component14to be grasped is formed, for example, of a display hand15, which has to be fitted onto an arbour of the timepiece. Of course, other components14can be handled by means of grasping system10according to the invention, particularly arbours, wheels, springs . . . .

In the following description, a vertical axial orientation along the general axis A1of tweezers12will be used in a non-limiting manner.

Tweezers12comprise first and second branches16,18which are joined at a first axial end20of the tweezers and which form a grasping pincer22at the second axial end of the tweezers in order to allow component14to be grasped by pincer22, by a manual manipulation of tweezers12.

Branches16,18are made of an electrically conductive material and they are placed at a determined potential, for example earth.

In accordance with the teaching of the invention, the first branch16comprises at least one electrostatic grasping surface24provided for grasping, by electrostatic attraction, a component14made of a conductive or semiconductor material, particularly hands15made of silicon-based crystalline material. Prior to being grasped, component14is placed on a support (not shown) made of electrically conductive material, placed at a determined potential corresponding to the potential of branches16,18, for example earth.

According to the embodiment shown, the electrostatic grasping surface24is formed by the outer surface of an insulating envelope30which covers electrode26. Electrode26is supplied with electric current by a powering device28.

Insulating envelope30is made of a dielectric material and it entirely covers electrode26. Insulating envelope30has a parallelepiped shape here. In order to guarantee a sufficient electrostatic attractive force with a reasonable voltage, the thickness of insulating envelope30, between electrode26and electrostatic grasping surface24, must be relatively small.

Advantageously, electrode26and insulating envelope30are arranged on the outer face32of the first branch16, such that electrostatic grasping surface24is orientated on the side opposite axis A1. Insulating envelope30is made of a synthetic material whose surface appearance is provided to allow a non-aggressive contact between component14and grasping surface24, so as not to alter the surface appearance of component14.

According to the embodiment shown here, powering device28is carried by the first end20of tweezers12and it is electrically connected to electrode26by a wire34. Powering device28includes, for example, a rechargeable battery and a high voltage generator (from 0.01 to 10 kV).

Powering device28comprises a control member36, which allows the user of tweezers12to manually control M the powering of electrode26to cause the electrostatic attraction of component14and thus to hold it pressed against electrostatic grasping surface24, as shown inFIGS. 1 and 2.

It will be noted that the intensity of the electrostatic attractive force for holding component14pressed against electrostatic grasping surface24is relatively low because of the low weight of a component14, such as a display hand15. Consequently, during certain assembly operations of component14, for example during assembly of hand15on an arbour, if it is held in position on the arbour by a mechanical force such as a gripping force, it is not indispensable to implement any particular control strategy of powering device18in order to release component14.

Control member36can be formed by a switch and, preferably, when the user stops powering electrode26, an electric power control strategy is implemented in order to release component14, for example by causing several alternating pulses of decreasing amplitude.

The operation of tweezers12according to the first embodiment of the invention is set out below.

When the user, generally a watchmaker, is handling and assembling components14which are not particularly fragile, for example components14made of brass, then he uses the conventional pincer22for grasping the component14and positioning it in the timepiece, simply by exerting mechanical pressure with his fingers on branches16,18of tweezers12.

When the user is handling and assembling components14that must be subjected to particular precautions to avoid damaging or scratching the same, for example silicon hands15, then he controls the powering of electrode26by means of switch36, which charges the insulating envelope30by producing, on electrostatic grasping surface24, an attraction force which enables component14to be grasped without needing to exert any mechanical pressure thereon. The user can then move component14in the timepiece in order to position it, then release component14by again acting on switch36.

It should be noted that since the component14made of conductive or semiconductor material is placed on a support at the same potential as branches16,18, which here is earth, then component14is itself at earth. When electrostatic grasping surface24approaches component14, the powering of electrode26causes a difference in potential between electrode26and component14, which generates an electric field and an electrostatic attractive force. Electric charges appear on electrostatic grasping surface24and on component14. When the electrostatic force is sufficient, component14will be pressed against electrostatic grasping surface24. Since the majority of the electric charges mobilised in component14remain on component14, the electrostatic attractive force is maintained which enables component14to be moved while keeping it pressed against electrostatic grasping surface24, until it is released by action on switch36.

The second embodiment, which is shown inFIGS. 3 and 4, will now be described, with particular reference to the technical features that differentiate this second embodiment from the first embodiment.

According to the second embodiment, powering device28is offset relative to tweezers12, the electrical connection wire34extending from tweezers12to powering device28. Moreover, control member36is formed by a pedal38, which enables the user to vary the intensity of the electrostatic attractive force, on electrostatic grasping surface24, as a function of the force that he exerts on pedal28with his foot.

FIG. 3shows a support39, on which component14is placed prior to being grasped. As mentioned previously, support39is placed at the same electric potential as branches16,18of tweezers12, here it is placed at earth.

In the second embodiment, electrostatic grasping surface24has at least one guide portion40,42provided for forcing component14to occupy a determined position on electrostatic grasping surface24.

FIG. 4shows first and second guide portions40,42, which are arranged on electrostatic grasping surface24in order to form complementary housings for hands15shown in dotted lines.

According to the example shown, the first guide portion40extends over the entire width of grasping surface24and it has the shape of an end section of hand15located on the side of the axis of rotation thereof. The first guide portion40is formed here by a recess delimited by two opposite edges44,46, which force hand15to be orientated along a transverse direction relative to axis A1, as shown inFIG. 3. Thus, hand15is not only held on electrostatic grasping surface24by the electrostatic attractive force, but it is also held in a determined position relative to electrostatic grasping surface24which then facilitates the positioning of hand15by the user in the timepiece for the assembly thereof.

According to the example shown, the second guide portion42is a housing that has the shape of a half-disc but it could take any other shape adapted to the shape of the component14to be handled.

According to an improvement of this second embodiment, the first guide portion40includes, opposite the arbour hole for hand15, an orifice48for receiving the axial end section of the arbour on which hand15will be mounted. Thus, when the user positions hand15in order to mount it on the arbour, he can exert pressure on hand15with tweezers12without directly abutting the end of the arbour.

Guide portions40,42are formed here by hollows shapes, but they could also be made in the form of ribs delimiting complementary housings for portions of the component14to be handled.

Of course, guide portions40,42can also be arranged on grasping surface24of the first embodiment.

Advantageously, at least one part of the electrostatic grasping surface24belongs to an added element50, which is removably secured to first branch16. According to the example embodiment shown, the added element50is formed by a plate of dielectric material, which is snap fitted to a plate52of dielectric material. Plate52is secured to the first branch16of tweezers12, for example by bonding, and it comprises a housing that receives electrode26. The added element50and plate42together form insulating envelope30which encloses electrode26.

The advantage of the added element50is that it facilitates the changing of electrostatic grasping surface24and thus allows the use of an electrostatic grasping surface24whose raised portions40,42are adapted to the component14to be grasped. Thus, if one wishes to handle silicon wheels, one only has to replace the added element50for hands15by an added element50fitted with portions40,42that complement the wheel to be grasped.

According to a variant (not shown), insulating envelope30can be entirely secured in a removable manner to tweezers12, which, if necessary, enables tweezers12to be used without the electrostatic grasping surface24.

The operation of the grasping system according to the invention will now be described with reference to the second embodiment.

In order to grasp a silicon hand15, the user moves electrostatic grasping surface24close to the support carrying hand15, approximately aligning hand15with the first guide portion40. Simultaneously, the user presses on pedal38to power electrode26and gradually increase the electrostatic attractive force until hand15is pressed against electrostatic grasping surface24. Due to the attraction force and due to the appropriate shape of the first guide portion40, hand15positions itself in a suitable manner in the first guide portion40, such that the arbour hole thereof faces orifice48.

The user then carries hand15with tweezers12to the timepiece in which it has to be assembled. The user then fits hand15onto the corresponding arbour of the timepiece by threading hand15onto the arbour until the free end of the arbour is accommodated in orifice18of electrostatic grasping surface24.

When hand15is fitted, the user raises the pedal38which cancels the electrostatic attractive force and releases hand15, the latter being in any event held on the arbour via its fit, similar to driving in.

The invention has been described with reference to tweezers12that comprise an electrostatic grasping surface24solely on the first branch6. Of course, the second branch18of tweezers12could also include an electrostatic grasping surface24similar to that previously described. It could comprise guide portions40,42, different from those of the first branch16, which would increase the number of components able to be grasped by electrostatic attraction using the same tweezers12.