Gripping unit and a method for gripping a paper
A gripping unit for gripping a paper from a top surface of a stack includes a first and a second friction wheel having rotation axes that are mainly parallel with respect to each other. The friction wheels are arranged to exert a friction force on sections of a paper. Further, the gripping unit comprises an actuator on which the first friction wheel is mounted for moving the first friction wheel towards the second friction wheel. The first friction wheel is arranged to rotate with respect to its axis during the movement towards the second friction wheel such that a paper section on which the first wheel exerts the friction force is forced into the direction of the second friction wheel.
1. A gripping unit for gripping a paper from a top surface of a stack, comprising a first friction wheel and a second friction wheel, said first friction wheel and second friction wheel having rotation axes that are mainly parallel with respect to each other and being arranged to exert a friction force on sections of a paper, the gripping unit further comprising an actuator on which the first friction wheel is mounted for moving the first friction wheel towards the second friction wheel, wherein the first friction wheel is arranged to rotate with respect to its axis during the movement towards the second friction wheel such that a paper section on which the first wheel exerts the friction force is forced into the direction of the second friction wheel, said gripping unit further comprising an airflow generator providing a flow of air between a paper being gripped and at least one of a surface below the paper and a surface above the paper.
2. A gripping unit according to claim 1 , wherein the first friction wheel is arranged to rotate with respect to its axis during the movement towards the second friction wheel such, that a contact portion of the first friction wheel exerting the friction force on the paper section is substantially moving towards the second friction wheel.
3. A gripping unit according to claim 1 , wherein the second friction wheel is arranged to rotate with respect to its axis during the movement of the first friction wheel such, that a contact portion of the second friction wheel exerting the friction force on a second paper section is substantially moving towards the first friction wheel.
4. A gripping unit according to claim 1 , wherein the movement of the first friction wheel forms substantially a translation.
5. A gripping unit according to claim 1 , wherein the rotation of the first friction wheel is driven by the actuator for moving the first friction wheel towards the second friction wheel.
6. A gripping unit according to claim 1 , wherein the first friction wheel is driven by a tooth wheel transmission.
7. A gripping unit according to claim 1 , wherein the first friction wheel is fixedly provided with a gear wheel cooperating with a gear rack that is fixed with respect to the axis of the second friction wheel.
8. A gripping unit according to claim 1 , wherein the first friction wheel is mounted on a first axle being provided with one or more additional friction wheels.
9. A gripping unit according to claim 1 , wherein the second friction wheel is mounted on a second axle being provided with one or more additional frictional wheels.
10. A gripping unit for gripping a paper from a top surface of a stack, comprising a first friction wheel and a second friction wheel, said first friction wheel and second friction wheel having rotation axes that are mainly parallel with respect to each other and being arranged to exert a friction force on sections of a paper, the gripping unit further comprising an actuator on which the first friction wheel is mounted for moving the first friction wheel towards the second friction wheel, wherein the first friction wheel is arranged to rotate with respect to its axis during the movement towards the second friction wheel such that a paper section on which the first wheel exerts the friction force is forced into the direction of the second friction wheel, said gripping unit further comprising a guiding element for removing from the stack an element having a surface above the paper to be gripped.
11. A gripping unit for gripping a paper from a top surface of a stack, comprising a first friction wheel and a second friction wheel, said first friction wheel and second friction wheel having rotation axes that are mainly parallel with respect to each other and being arranged to exert a friction force on sections of a paper, the gripping unit further comprising an actuator on which the first friction wheel is mounted for moving the first friction wheel towards the second friction wheel, wherein the first friction wheel is arranged to rotate with respect to its axis during the movement towards the second friction wheel such that a paper section on which the first wheel exerts the friction force is forced into the direction of the second friction wheel, wherein the second friction wheel is allowed to rotate in one direction only.
12. A method for gripping a paper from a top surface of a stack, comprising the steps of
exerting friction forces on a first and second section of the paper via a first friction wheel and a second friction wheel, respectively, the friction wheels having rotation axes that are mainly parallel with respect to each other, and
moving the first friction wheel towards the second friction wheel while rotating the first friction wheel with respect to its axis such that the first paper section is forced into the direction of the second friction wheel, and
providing a flow of air between a paper being gripped and at least one of a surface below the paper and a surface above the paper.