Background of the Invention

This invention relates to a hand power tool mechanism having a stationary handle, and a drive lever connected to said stationary handle by a joint.

More particularly the invention relates to a bone cement caulking gun. Bone cement is used for the anchoring of prosthetic replacements in human bones. It is prepared by mixing a powder component (mainly consisting of polymethylmethacrylate beads and a polymerization catalyst) with a liquid component (mainly consisting of methylmethacrylate monomer) and is applied to the site of implantation by said caulking gun which is used to expel the bone cement mixture in a state of relatively high viscosity. For this purpose the mixed bone cement is filled into a syringe and is extruded by a piston. The power for driving the piston is produced by the action of the hand through a drive mechanism of the friction or ratchet type. In conventional bone cement caulking guns the handles are arranged in a simple kinematic pair, whereby the position of the strongest fingers is unfavorable for delivering power to the piston.

Summary of the Invention

The invention as claimed is intended to remedy these drawbacks. It solves the problem of how to design a hand power tool with favorable conditions for delivering hand power to the advance mechanism of the tool, in particular a bone cement caulking gun. The invention is equally useful for other hand powered tools, like guns for delivering silicone rubber, scissors or pliers.

The advantages offered by the invention are mainly the better utilisation of hand power.

In a preferred embodiment the four joints of the four-bar linkage mechanism are arranged in such a way that an optimal force/travel ratio for the fingers of the hand results. In particular the two lines connecting the proximal with the distal joints preferably intersect at a point distally to the mechanism, preferably at 0,5 to 2,5 lengths of the linkage closure bar.

In a further preferred embodiment of the hand power tool mechanism according to the invention the kinematic joints are replaced by flexible joints, preferably made of elastomer allowing a simpler construction and avoiding cleaning problems especially for surgical applications.

The hand power tocl mechanism according to the invention can be used e.g. for a bone cement or silicone rubber caulking gun, for scissors or pliers.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For the better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which are illustrated and described preferred embodiments of the invention.

Brief Description of the Drawings

In the drawings:

Fig. 1 is a sectional view of a conventional bone cement caulking gun.

Fig. 2 is a perspective view of a conventional scissors.

Fig. 3 is a four bar linkage caulking gun according to the invention.

Fig. 4 is a sectional view of a four bar linkage scissors according to the invention.

Description of the Preferred Embodiments

Fig. 1 represents a conventional bone cement caulking gun with a stationary handle 1 connected to the body 2 and a movable handle 3 connected to the stationary handle 1 by means of the joint 4. Movement of the handle 3 as indicated by arrow 5a results in the movement indicated by arrow 7 of the bar 6 which advances rod 9 via pusher 8. Piston plate 10 advances forwardly as indicated by arrow 36 for each squeeze of the handles 1,3 extruding material 11 from the syringe 12 through a nozzle 13. On return stroke as indicated by arrow 5b the rod 9 is prevented from retracting by a brake 14. Position of the hand on the handles 1,3 is indicated by circles 21 for the palm, 22 for the index, 23 for the middle finger, 24 for the ring-finger and 25 for the little finger with lever arms 31,32,33,34,35 with respect to joint 4. The strongest fingers (index and middle finger) have the shortest lever arms 32,33. The energy transmitted to the piston plate 10 is equal to the product of the force and travel cf each of the fingers. The utilisation of the strongest fingers of the hand is consequently poor.

Number of strokes per minute one can execute with the hand is obviously limited and so is the power delivered to the tool.

Fig. 2 represents conventional scissors where two handles 61, 62 are connected at the joint 63. The position of the hand is identical to that described in Fig. 1 and consequently the power delivered to the blades 64,65 does not correspond to the full potential of the hand.

Fig. 3 represents a caulking gun according to the invention. Its hand power tool mechanism comprises a stationary handle 101, a drive lever 102 connected to said stationary handle 101 by a joint 103, a movable handle 104 connected to said drive lever 102 by a joint 105 and a linkage closure bar 106 connected to both said movable handle 104 and said stationary handle 101 by joints 107 and 108 respectively. Said stationary handle 101, drive lever 102, movable handle 104, linkage closure bar 106 and said four joints 03,105,107,108 are forming a four bar linkage mechanism. The movement of said movable handle 104 (as shown by arrow 109} from the open position to the closed position (as represented by the dotted lines) and back is defined by the kinematics of the four bar linkage. Position of the palm and fingers is indicated by the circles 111,112,113,114,115. Position of the strongest fingers (index and middle finger) is favorable for power delivery through a mechanism sirr.il r to the one described in Fig. 1.

Fig. 4 represents a four bar linkage scissors according tc the invention. Stationary handle 91 is connected to the movable handle 94 with two bars 92,96 through the joints 93,95,97 and

98. Hand power is delivered to the blades 99 and 100 through the four-bar linkage movement of the handles 91 and 94 with optimum utilization of the fingers.