Four-bar linkage pruning shears

Abstract

The present invention relates to a shears comprising a four-bar-linkage hand power mechanism wherein a spring is attached to two of the four bars at positions the distance of which increases as the shears are cutting.

Description

[0001] FOUR-BAR LINKAGE PRUNING SHEARS

[0002] DESCRIPTION

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a shears comprising a four-bar-linkage hand power mechanism wherein a spring is attached to two of the four bars at positions the distance of which increases as the shears are cutting.

[0005] BACKGROUND

[0006] A four-bar linkage hand power tools are known from S. Tepic, US 5052243A, Hand power tool mechanism disclosing applications to caulking guns and garden or pruning shears. While the caulking guns according to that patent have seen significant commercial applications, to the best knowledge of the inventor, the pruning shears have not been commercialized.

[0007] US 5052243A does not disclose how the obligatory return spring would be implemented in that invention. In conventional, single-pivot shears, the return springs are of the compression type. In most cases, they are made from rolled sheet metal and are known as volute springs, placed between the handles, and close to the pivot.

[0008] SUMMARY OF THE INVENTION

[0009] The present invention discloses a return spring for garden shears incorporating a four-bar- linkage hand power mechanism whereby the spring is of tension-type and attached to two of the four bars at positions the distance of which increases as the shears are cutting.

[0010] Tension springs are not prone to buckling, they are robust against fatigue and free from internal friction, unlike volute springs. An aspect of the present invention relates to a shears comprising a four-bar-linkage hand power mechanism wherein a spring of tension-type is attached to two of the four bars at positions the distance of which increases as the shears are cutting. In particular embodiment, the shears is adapted for garden work, particularly for pruning actions.

[0011] A further aspect of the invention relates to the use of the shears for gardening work.

[0012] DESCRIPTION OF FIGURES

[0013] Figure 1 : Photographs showing front and back views of the pruning shears according to the invention in closed and open positions, respectively.

[0014] Figure 2: Orthogonal views as a technical drawing of the pruning shears in the closed position.

[0015] Figure 3: Orthogonal views as a technical drawing of the pruning shears in the open position.

[0016] DETAILED DESCRIPTION

[0017] The present invention relates to a shears comprising an lower blade (9) and an upper blade (10) adapted for sliding against each other in a cutting action, a four bar linkage mechanism comprising a lower blade support (1 ), an upper blade support (2), a handle (3), and a link (4) and a return spring (12) wherein the ends of the return spring (12) are attached to two of said bars at positions (13, 14) the distance between which increases as the shears are cutting, wherein the return spring (12) is a tension-type spring.

[0018] In certain embodiments, the lower blade (9) and the lower blade support (1 ) attached thereto form a stationary grip element of the shears. The upper blade (10) and the upper blade support (2) attached thereto together with the handle (3) and the link (4) may form a movable grip element of the shears. The linkage between the lower blade (9) and the upper blade (10) or the lower blade support (1 ) and the upper blade support (2), respectively, may be provided by a plurality of pivots (5, 6, 7 and 8) comprising a first pivot (5) which connects the lower blade (9) and the upper blade (10) and provides the center of rotation between them. The shears may further comprise a second pivot (6) connecting the upper blade (10) with the link (4), a third pivot (7) connecting the handle (3) with the link (4), and a fourth pivot (8) connecting the upper blade support (1 ) with the handle (3). The ends of the return spring (12) may be attached to the upper blade support (2) and the link (4), e.g., via posts protruding from the surface of the respective element.

[0019] The shears may further comprise a lock (11 ) adapted for keeping the shears in closed position when not in use. The lock may be attached to the lower blade support (1 ) and adapted for engagement with the handle (3).

[0020] In certain embodiments, the distance between return spring attachment positions (13) and (14) is at its minimum when the shears are in an open position. Thus, the distance between spring attachment positions (13) and (14) and hence the return force of spring (12) increases as the shears are closing in a cutting action. The shears' maximum limit of opening may be defined by a contact position (15) between the upper blade support (2) and link (4).

[0021] In certain embodiments, the return spring (12) is under residual tension, particularly between

[0022] 1 and 3 N, in the position at the maximum limit of opening. In further embodiments, the return force between the upper blade support (1 ) and the handle (3) is substantially constant throughout the range from open to closed position. I .For example, the return spring may be adapted to provide a return force at the grip elements between 1 and 15 N, preferably between

[0023] 2 and 10 N, and most preferably between 3 and 7 N.

[0024] In certain embodiments, the shears further comprises a thumb support (16) attached to the lower blade support (1 ). The thumb support is optional -- if used, it may be affixed to the lower blade support (1 ), e.g., by a peg at the upper end (not visible) and, e.g., a screw at the lower end.

[0025] Preferred embodiments of the present invention are described in more detail in the following by reference to the appended Figures.

[0026] Figure 1 a shows the front view of the shears according to the invention in the closed position. The lower blade support 1 , the upper blade support 2, the handle 3, and the link 4 comprise the four-bar linkage mechanism. The pivots 5, 6, 7, and 8 close the linkage. The lower blade 9 and the upper blade 10 slide past each other in the cutting action. The pivot 5 is the main pivot and the center of rotation of the blades 9 and 10. The lock 11 , keeps the shears in closed position when not in use.

[0027] Figure 1 b shows the back side of the shears in the open position. The return spring 12 is attached to posts 14, and 13 on the upper blade support 2 and link 4, respectively. Note that the distance between posts 13, and 14 is at its minimum when the shears are in the open position. The shears' opening limit is provided by the contact between the upper blade support 2 and link 4 at point 15. In this position, the spring is under residual tension, i.e., stretched beyond its unloaded length. As the shears are closing in the cutting action the distance between posts 13 and 14 increases, and hence the return force of spring 12. The length of the spring, its stiffness, and the preload in the closed position provide design freedom to make the return force between handles 1 and 3, relatively constant throughout the range from open to closed position. Optional thumb support 16, is a unique feature of the shears according to this invention.

[0028] Figure 2 is the technical drawing showing the shears in all orthogonal views when in a closed position. The main parts are numbered as in Figure 1.

[0029] Figure 3 is the technical drawing showing the shears in all orthogonal views when in an open position. The main parts are numbered as in Figures 1 and 2.

[0030] The spring used in the shears of the present invention may be made from stainless steel.

[0031] In certain embodiments, the shears and its constituents may have dimensions as indicated in the following. The thickness of the spring wire is 1 .0 mm. The outside diameter is 8.0 mm. The unloaded length is 42 mm, and the maximum active length (in a closed position) is 66 mm. In the open position, the length is 53 mm. In the open position, the residual force between the handles is about 3 N. To fully close the shears, the handles need to be squeezed by about 7 N. An average hand can generate about 200 N fingers-to-palm force.

[0032] The shears as disclosed herein is particularly suitable for gardening work, e.g., for pruning trees and shrubs.

Claims

CLAIMS1. A shears comprising a lower blade (9) and an upper blade (10) adapted for sliding against each other in a cutting action, a four bar linkage mechanism comprising a lower blade support (1 ), an upper blade support (2), a handle (3), and a link (4) and a return spring (12) wherein the ends of the return spring (12) are attached to two of said bars at positions (13, 14) the distance between which increases as the shears are cutting, wherein the return spring (12) is a tension-type spring.

2. The shears of claim 1 wherein the lower blade (9) and the lower blade support (1 ) attached thereto form a stationary element.

3. The shears of claim 1 or 2 wherein the upper blade (10) and the upper blade support (2) attached thereto together with the handle (3) and the link (4) form a movable element.

4. The shears of any one of claims 1 -3 wherein the linkage between the lower blade support (1 ) and the upper blade support (2) is provided by a plurality of pivots (5, 6, 7 and 8) comprising a first pivot (5) which connects the lower blade (9) and the upper blade (10) and provides the center of rotation between them.

5. The shears of claim 4 further comprising a second pivot (6) connecting the lower blade support (1 ) with the link (4), a third pivot (7) connecting the handle (3) with the link (4), and a fourth pivot (8) connecting the upper blade support (2) with the handle (3).

6. The shears of any one of claims 1 -5, wherein the ends of the return spring (12) are attached to the upper blade support (2) and the link (4).

7. The shears of any one of claims 1 -6 further comprising a lock (11 ) adapted for keeping the shears in closed position when not in use, wherein the lock is preferably fixed to the lower blade support (1 ) and adapted for engagement to the handle (3).

8. The shears of any one of claims 1 -7, wherein the distance between spring attachment positions (13) and (14) is at its minimum when the shears are in an open position.

9. The shears of any one of claims 1 -8, wherein the distance between spring attachment positions (13) and (14) and hence the return force of spring (12) increases as the shears are closing in a cutting action.

10. The shears of any one of claims 1 -9, wherein the shears' maximum limit of opening is defined by a contact position (15) between the upper blade support (2) and link (4).11 . The shears of any one of claims 1 -10, wherein the spring (12) is under residual tension in the position at the maximum limit of opening.

12. The shears of any one of claims 1 -11 , wherein the return force between the upper blade support (1 ) and the handle (3) is substantially constant throughout the range from open to closed position.

13. The shears of any one of claims 1 -12 further comprising a thumb support (16) attached to lower blade support (1 ).

14. The shears of any one of claims 1 -13, wherein return spring (12) is adapted to provide a return force at the handles between 1 and 15 N, preferably between 2 and 10 N, and most preferably between 3 and 7 N.

15. Use of a shear of any one of claims 1 -14 for gardening work.

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