The present invention relates to a paper punch for office use. Background of the Invention

A known paper punch of this type is disclosed in US 4,466,322 and comprises a base having a base cover for supporting a stack of paper; an upstanding support structure comprising a pair of first and second hollow upright guide members mounted on the base and spaced apart a predetermined distance relative to each other. The guide members form a guide for respective punch holder blocks supporting substantially tubular punches having an upper head portion received within said punch holder blocks, and a bottom punching end for punching and perforating the stack of paper. A handle is pivotally supported in an upper portion of the support structure for rotation about a horizontal pivot axis relative the said base and is coupled to the punch holder blocks for slidingly moving said punch holder blocks within said guide members in a substantially vertical direction towards and away from the base. The punches are received in mating insertion bores in the bottom portion of the punch holder blocks and are secured therein by set screws extending into the punch holder blocks. On pivoting the handle downwardly about its pivot axis, the punch holder blocks are moved down in the vertical direction. Pads are provided on the base at positions at which the tip ends of the punches are to abut after penetrating the stack of paper disposed on the base.

With the above-described conventional paper punch, the sharp bottom ends of the punches wear over time so that the cutting performance of the punches is degraded. Further, it may be desired to change the size of the hole to be formed through the stack of paper. In both cases, it is necessary to exchange the punches. For exchanging the punches, it is necessary to remove the set screws and subsequently withdraw the punches from the insertion bore, then to insert new punches into the insertion bores of the punch holder blocks and thereafter to fix the new punches by the set screws. This exchange of the punches therefore is time consuming and troublesome, especially since the punches are to be inserted into the insertion bores located at the bottom of the punch holder blocks, so that it is impossible to carry out the insertion while observing the insertion bore. Accordingly, it is difficult to insert the head portion of the punches into these holes.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a paper punch in which replacement of punches is simplified.

According to a first aspect of the invention, with a paper punch as set out above, the punch holder blocks are provided with a horizontal extension extending therefrom and from said support structure over said base cover and forming a guide for a respective punch holder slidingly supported within the extension in a substantially horizontal direction parallel to said base. Each punch holder is adapted to receive the head portion of a punch for movement between an operative position within the punch holder block and a retracted position within said extension. Locking means are provided to lock said punch holder within the extension in the operative position. In this manner, the punch holder blocks simply may be unlocked and slid away from the punch holder blocks so that the punches are freely accessible and may be withdrawn in an upward direction. The insertion of a new punch is possible in an equally simple manner by inserting the respective new punch into the punch holder and sliding the punch holder into its operative position.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

Fig. 1 is a perspective view showing an embodiment of the paper punch according to the invention in a rest position with a stack of paper partly arranged on a base cover of the paper punch; Fig. 2 is a view similar to Fig. 1 after pushing the stack of paper with its front edge into a gap formed in a support structure below the punches guided therein;

Fig. 3 is a perspective view showing the paper punch of Figs. 1 and 2 after moving a handle actuating the punches and pivotably mounted in the top portion of the support structure downwards, thereby punching holes into the stack of paper;

Fig. 4 is a perspective view of the paper punch of Figs. 1 to 3 with a front cover of the support structure removed, together with a detail indicated in Fig. 4 by a dashed circle and showing in larger scale of one of two guide members and an associated punch holder block in the operative position of the punches;

Fig. 5 is a view similar to Fig 4, but showing the punch holder blocks after withdrawing the punch holders and the punches from the support structure into a retracted position for changing the punches;

Fig. 6a to 6d are perspective views of details of one embodiment of the invention of a punch holder block and the parts associated therewith; and

Fig. 7a to 7f are perspective views of showing further details of the embodiment of the punch holder block and the parts associated therewith in more detail.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described by way of example with reference to the accompanying drawings. Fig. 1 to 5 give a general overview of the paper punch according to a preferred embodiment as well as the mode of operation thereof. As may be seen from Fig. 1 , a support structure indicated generally at 20 is supported by a base 10. A generally U shaped handle 30 is pivotably supported in an upper portion of said support structure 20 for rotation about a horizontal pivot axis relative to the base 10. As will be set out below in detail with reference to Figs. 4 and 5, the handle 30 is coupled to punch holder blocks 40 for slidingly moving these punch holder blocks within guide members 23 disposed the support structure 20 in a substantially vertical direction towards and away from said base 10.

In Fig. 1 , a stack of paper 14 is partly disposed on a base cover 17 on the top surface of the base 10 to show a gap for inserting the stack of paper at the bottom end of the support structure 20 and below the path of movement of punches (not shown in Fig. 1 ). Pads 1 1 are provided on the top surface of the base for engagement with the bottom cutting edges of the punches after these punches have penetrated the stack of paper. The support structure 20 is covered by a rear cover 21 and a front cover 22 to avoid the risk of injuries by the moving parts of the support structure 20.

In Fig. 2, the stack of paper has been pushed into the gap at the bottom end of the support structure 20 and below the path of movement of the punches. Setting means 15 are provided in a conventional manner to adjust the position of the the stack of paper with respect to the punches.

Fig. 3 shows the paper punch after the handle 30 has been pressed downwardly until the punching or perforating operation of the stack of paper is completed and the cutting edges of the punches have been brought into engagement wit the pads 1 1 .

In Figs. 4 and 5, the embodiment of the paper punch is shown after removing the front cover 22 of the support structure 20. In these Figs. 4 and 5, details the support structure 20 and of one of the punch holder blocks in the region surrounded by dashed circles in the left hand portions of these Figs, are shown on a larger scale in the right hand portion thereof.

As may be seen from Fig. 4, the free ends of legs 33 of the handle 30 are pivotally mounted about shafts 31 at the top portion of the support structure 20. The support structure comprises a pair of first and second hollow upright guide members 23 mounted on said base 10 and spaced apart a predetermined distance relative to each other. The guide members 23 form a guide for respective punch holder blocks 40 supporting substantially tubular punches (45) having a bottom punching or cutting end for punching and perforating the stack of paper 14. The punch holder blocks 40 are actuated in the embodiment shown via links 32 connected between the upper end of the punch holder blocks 40 and a pivot axis of the leg 33 offset with respect to the shaft 31 thereof

As will be explained in detail below with reference to Figs. 6 and 7, the punch holder blocks 40 have a horizontal extension 41 extending therefrom and from said support structure 20 over said base cover 17 and forming a guide for a respective punch holder 44 slidingly supported within the extension 41 in a substantially horizontal direction parallel to said base 10.

As may be seen from Figs. 6 and 7, the extensions 41 of the punch holder blocks 40 form guides for respective punch holders 44 which are adapted to receive the head portion 45a of a punch 41 for movement between an operative position (Fig. 4 and Fig. 6b) within said punch holder block 40 and a retracted position within said extension 41 (Fig. 5 and 6c). The extensions 41 of said punch holder blocks 40 have an U-shaped cross section comprising a bottom portion 41 a and lateral flanges 41 b, the flanges 41 b being provided with guide slots 42 extending substantially horizontally. The slots 42 end in a vertically upwardly directed end portion 42a adjacent said guide members 23. A locking pin 43 extends through a transverse vertically extending groove 44a provided in the bottom surface of the punch holder 44 and is guided within the slots 42 and is movable upwardly relative to said punch holder 44 within said groove 44a to engage within the vertical end portions 42a of said slots 42 to lock the punch holder 44 in said working position wherein the punch 45 is positioned within said punch holder block 40. The punch holder 44 supports the lower ends of spring means 46a, 46b) for biasing the locking pin 43 in an upward direction via an angled lever 47 acting from below against the locking pin 43. The lever 47 comprises at a first end a support pin 47a extending into a hole 44c in a top surface of the punch holder 44 for restraining the lever 47 in the longitudinal direction of the extension 41. The lever 47 further comprises at the end opposite to the pin 47a a release portion 47b cooperating with release means formed by a cap 48 covering the upper side and part of the flanges 41 b of the extension 41. The cap 48 is mounted for a limited pivot movement about the outer ends of the locking pin 43 which extend beyond the flanges 41 of the extension 41 into recesses 48a on the inner side of side walls of the cap 48.

The cap 48 further comprises an actuation protrusion 48b at the bottom surface of its top wall, said actuation pin 48b adapted to act on the the release portion 47b of the lever 47 for moving the locking pin 43 downwardly to release it from the vertical end portion 42a of the slots 42.

The punch holder 44 comprises a bifurcated extension 44b at its end directed to the punch holder block 40. This bifurcated extension 44b is configured and adapted to receive and hold a head portion 45a of a respective punch 45 opposite to the bottom cutting edge 45b thereof. This punch 45 extends from the bifurcated extension 44b through an elongated slot 41 c provided in the bottom portion 41 a of the extension 41 downwardly from the punch holder block extension 44. The slot 41 c further extends into the bottom surface of the punch holder block 40 as may be especially seen from Fig 7c. The punch 45 thereby is adapted to be moved by the punch holder 44 along this slot 41 c between an operative position within the punch holder block 40 and a position within the extension 41. In the latter position, the punch is readily accessible in front of the front cover 22 of the upstanding support structure 20 and may be removed and replaced. In the operative position of the punch 45, the head portion 45a thereof is clamped between the bifurcated extension 44b and a complementary configuration of the bottom end of the punch holder block 40 and is locked in this position by the engagement of the locking pin 43 in the angled end portions of the slots 42 of the extension 41. On pressing on cap 48, the protrusion 48a thereof acts on the end 47b of the lever 47 to disengage the pin 43 from the end portions 42a of the slots 42, such that the punch holder 44 and thereby the punch may be moved away from the punch holder block 40 into the removal position of the punch. In spite of the fact that a preferred embodiment of locking means have been set out in detail above, other designs of releasable locking means for locking the punch holders in their operative position may be provided.

Fig. 7 further shows a preferred embodiment of the punch holder block 40 and the extension 41 thereof wherein these two parts are formed as an integral structure, for instance as a casting, which in this case is subdivided into two halves along a vertical and longitudinal plane of the block 40 and the extension 41 to facilitate the fabrication and machining thereof. Mating protrusions and recesses between the two halves ensure a rigid interlocking of these two halves which may be secured to one another by means of fasteners 40d.