Locking device for a hand tool

Tools – Tool jaw – With means to immobilize jaws

Reexamination Certificate

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Details

C081S302000, C081S321000, C081S423000, C081S424000

Reexamination Certificate

active

06308597

ABSTRACT:

FIELD OF INVENTION
The present invention relates to a hand tool to lockably apply a compressive or separating force on a workpiece, said tool comprising two shafts pivotable in relation to each other, the ends of which form two jaws for cooperation with the workpiece and which, spaced from these ends, are joined together by a spring element with an action corresponding to a compressible compression spring, and a locking device between said spring element and said jaws, said locking device comprising a toothed locking element protruding from one of the shafts and a locking device on the other shaft arranged by engagement with the toothed locking element to releasably lock the position of a joint about the spring element.
DESCRIPTION OF THE PRIOR ART
Patent specification EP 0403517 describes a tool according to the above, comprising two shafts with jaws, a spring element and a locking device, which locking device produces a movable joint. The movable joint enables a combination of high clamping force and large working range. To obtain a high clamping force on workpieces of varying thicknesses the possible locked positions for the joint must be as close together as possible. The above patent suggests different designs of locking devices which can be divided into two main groups: shape-dependent and friction-dependent locking devices. Friction-dependent locking devices allow in principle stepless adjustment of the position of the joint, but have the drawback that they require considerable contact forces. These large contact forces require the locking element and locking member to be manufactured of high-strength material, thereby greatly increasing manufacturing costs. In practice, therefore, shape-dependent locking devices have come to be used for this type of hand tool, said locking devices comprising a toothed locking element protruding from one of the shafts and a locking member in the form of a catch on the other shaft, arranged by engagement in the toothed locking element to releasably lock the position of the joint. It has been found that a catch that is pivotably suspended in the second shaft offers particularly good function. The drawback with this type of locking device is that the teeth on the locking element can hardly be closer together than 2.5 mm if they are manufactured of metal with high precision, if a reliable locking function is to be obtained. This means that greater amplification than approximately 3 times the force cannot be obtained if an acceptable clamping function is to be obtained on workpieces of varying thicknesses when the tool is operated. with one hand. There has hitherto been no satisfactory solution to this limitation in force amplification. Furthermore, due to the demand for locking positions close together, and thus small teeth, it has hitherto been impossible to achieve a reliable locking device made from plastic, which is desirable since the tool can then be produced more cheaply.
SUMMARY OF THE INVENTION
The main object of the present invention is to provide a hand tool as described above consisting of two shafts with jaws, a spring element and a shape-dependent locking device which produces a movable joint, said locking device combining reliable locking function and tightly spaced locked positions for the joint.
This object is achieved with a hand tool to lockably apply a compressing or separating force on a workpiece, said tool comprising two shafts pivotable in relation to each other, the ends of which form two jaws for cooperation with the workpiece and which, spaced from these ends are joined together by a spring element with an action corresponding to a compressible compression spring, and a locking device between said spring element and said jaws, said locking device comprising a toothed locking element protruding from one of the shafts and a locking device on the other shaft arranged by engagement with the toothed locking element to releasably lock the position of a joint about which the shafts can pivot in relation to each other under influence of the spring element, said locking device comprising two or more catches and/or said locking element comprising two or more rows of teeth.


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