BACKGROUND OF THE INVENTION

The present invention relates to a safety cutter and more particularly pertains to a safety cutter with automatically retracts the blade into the housing after the blade leaves the cutting surface even if the trigger is not released.

A convention safety cutter usually comprises a housing which receives a trigger, a transmission member, a blade carrier and a blade. When the user pushes the trigger, the transmission member is driven to move the blade carrier forward, thus exposing the blade out of the housing to preform cutting operation. After the cutting operation is complete, a user is required to release the trigger to retract the blade into the housing. However, sometimes a user may inadvertently forget to release the trigger after the cutting operation, and the exposed blade may injure the user or other people near the user.

Besides, in conventional safety cutters, it is difficult to push the blade outward for a long distance. This is because in the trigger mechanism in conventional safety cutters, when a user presses the trigger for a certain distance (e.g. 1 mm), the trigger could only drive the blade to move outward for the same distance (e.g. 1 mm). Due to limitation in the space provided to accommodate the trigger mechanism in safety cutters, it is usually impossible for the blade to be pushed outward for a long distance. This would pose difficulties for users when it is necessary to cut through thicker materials.

BRIEF SUMMARY OF THE INVENTION

In view of the aforesaid disadvantages now present in the prior art, an object of the present invention is to provide a safety cutter which is capable of moving the blade outward for a longer distance than conventional safety cutters.

It is a further object of the present invention to provide a safety cutter wherein the blade carrier is releasably engaged with the transmission member to achieve automatic retraction of the blade into housing after the blade leaves the cutting surface even if the trigger is not released, thus improving safety of the cutter.

To attain these, the present invention comprises a housing which receives a trigger, a transmission member, a blade carrier and a blade. The housing has a front end with a blade opening for a blade to protrude outwards therefrom and a rear end opposite to the front end. The trigger is movable between an actuated positon and a rest position. The transmission member is engaged operatively with the trigger via a gear assembly to move between a biased transmission member retracted position when the trigger is at the rest position and a transmission member extended position when the trigger is at the actuated position. The blade carrier is transversely fixed in the housing for carrying the blade, and is releasably engaged with the transmission member and longitudinally movable between a biased blade carrier retracted position where the blade is entirely received within the housing and a blade carrier extended position where the blade is at least partially exposed out of the housing via the blade opening for performing cutting operation. The trigger comprises a handle portion exposed outside the housing and a trigger rack portion which extends from the handle portion into the housing in a direction which is substantially perpendicular to which the blade is moved. The transmission member comprises a transmission rack portion which extends longitudinally in a direction substantially parallel to which the blade is moved. The gear assembly comprises a first gear engaged operatively with the trigger rack portion, a second gear coaxially and rotationally engaged with the first gear via a gear rotations shaft and engaged operatively with the transmission rack portion. The first gear has a smaller number of teeth than the second gear. A first limiting member provided in the housing is configured to abut against a top portion of a rear wall of the trigger rack portion for preventing rearward movement of the trigger. A pair of second limiting members provided in the housing is positioned on two substantially opposite sides of the second gear for preventing longitudinal movement of the second gear.

The safety cutter further comprises a pusher received in the housing at a front end of the transmission member having a first inclined surface and a second inclined surface. At the blade carrier extended position, the blade carrier is pivotally rotatable between an unlifted position when no external force is exerted upon the blade and a lifted position when the blade is pressed upon a cutting surface to perform cutting operation. A first protrusion is provided on the blade carrier and cooperates with the first inclined surface for facilitating disengagement of the transmission member from the blade carrier when the blade carrier is pivotally rotated from the unlifted position to the lifted position. A second protrusion is provided on the blade carrier and cooperates with the second inclined surface for facilitating engagement of the transmission member with the blade carrier when the blade carrier is at the blade carrier retracted positon and the transmission member returns from the transmission member extended position to the transmission member retracted position as the trigger returns from the actuated position to the rest position.

The safety cutter further comprises a third protrusion extended upwards from the blade carrier which engages with a downward-facing recess at a top inner portion of the housing when the blade carrier is at the lifted position to prevent the blade carrier from returning to the blade carrier retracted position.

The recess has an inclined rear wall which extends from a rear bottom end of the recess upwards and forwards towards a rear top end of the recess for facilitating disengagement of the third protrusion from the recess when the blade carrier is returned from the lifted position to the unlifted position.

The blade carrier further comprises a first pin extending from a first side thereof which is inserted into and slides in a first guiding groove formed on a first inner wall of the housing, and a second pin extending from a second side thereof which is inserted into and slides in a second guiding groove formed on a second inner wall of the housing; the second guiding groove has a horizontal portion and an upward sloping portion for the second pin to slide therein when the blade carrier rotates upwards from the unlifted position to the lifted position.

The blade carrier further comprises a blade carrier spring with one end thereof coupled to the blade carrier and another end thereof coupled to the housing for biasing the blade carrier towards the blade carrier retracted position.

The transmission member further comprises a transmission spring with one end thereof coupled to the transmission member and another end thereof coupled to the housing for biasing the transmission member towards the transmission member retracted position.

The first protrusion is a cuboid which extends along a direction substantially parallel to which the blade is moved; the second protrusion is a cuboid which extends along a direction substantially perpendicular to which the blade is moved and forms an L-shape with the first protrusion.

The pusher comprises a lower pusher portion and an upper pusher portion extending upwards and inwards therefrom; the lower pusher portion is a cuboid with its top side coplanar with and substantially flushes against a top side of the first protrusion when the blade carrier is engaged with the transmission member and the blade carrier is at the unlifted position; the upper pusher portion has a rear side coplanar with and substantially flushes against a front side of the second protrusion when the blade carrier is at the blade carrier retracted position and the rear side reaches the second protrusion while the trigger returns from the actuated position to the rest position, a front side parallel to the rear side with its inner end extending inwards so that the front side is partially abutted against a rear side of the second protrusion when the blade carrier is engaged with the transmission member and the blade carrier is at the unlifted position, an inner side joining an inner edge of the rear side and an inner edge of the front side to form the first inclined surface, a bottom side with an outer portion which aligns with the top side of the lower pusher portion and a triangular-shaped inner portion which extends upwards and inwards from the outer portion to join a bottom edge of the inner side to form the second inclined surface.

