Structure of drive section of power tool

Abstract

.[.An output axis of a motor has an eccentric portion, a vibratory arm is vibratably supported at its central portion, connecting section of said vibratory arm with the eccentric portion is formed in shape of two crotches, the eccentric portion and the vibratory arm are connected to each other in a manner that the eccentric portion is inserted between the two crotches of the vibratory arm, thereby rotational movement of the output axis of the motor is converted into vibrational movement of the vibratory arm, and at least one of contact portion formed on the outer circumfrential surface of the eccentric portion or contact portions respectively formed on the inside surface of each of two crotches is formed in shape of a curved surface..]..Iadd.A power tool has a drive section with a shaft having a rotational axis and an eccentric portion offset from the rotational axis. An arm drivingly connects the shaft to a tool working member. The arm has one end formed in the shape of a fork with a pair of prongs, and is pivotable about a vibrating axis generally perpendicular to the rotational axis. A first contact portion on the eccentric portion engages a second contact portion on the prongs to convert rotational movement of the shaft about the rotational axis into pivotal movement of the arm about the vibrating axis to pivot the working member about the vibrating axis. At least one of the first and second contact portions has a curved surface of which a contour curves on a plane generally perpendicular to the vibrating axis..Iaddend.

What is claimed is: 
     
       1. Structure of drive section of a power tool for giving a swinging motion to a tool .[.such as a sander.]., which comprises: an output shaft portion of a motor having a rotational axis and an eccentric portion deviating from said rotational axis;   a vibratory arm capable of vibrating about a vibrating axis and holding said tool at its one end, said vibrating axis being perpendicular to said rotational axis; and   connecting section of the other end of said vibratory arm with said eccentric portion formed in shape of two crotches, said eccentric portion and said vibratory arm being connected to each other in such a manner that said eccentric portion is inserted between said two crotches of said vibratory arm, thereby rotational movement of said output shaft portion of said motor being converted into vibrational movement of said vibratory arm, said connecting section having a first contact portion formed on the outer circumferential surface of said eccentric portion and second contact portions respectively formed on the inside surface of each of said two crotches, and at least one of said first contact portion and each of said second contact portions comprising a curved surface of which a contour curves on a plane perpendicular to said vibrating axis.   
     
     
       2. The structure of drive section of the power tool according to claim 1, wherein said second contact portions comprise half pillar like projections of which axes are extended perpendicularly to the axial direction of said vibratory arm, and each of said half pillar like projections contacts said first contact portion. 
     
     
       3. The structure of drive section of the power tool according to claim 1, wherein said first contact portion comprises an outer circumferential surface of which a central part is raised in its radial direction so as to form said curved surface, and the top of said curved surface contacts said second contact portions. 
     
     
       4. The structure of drive section of the power tool according to claim 1, wherein a ring is attached to the outer circumferential portion of said eccentric portion, and an outer surface of said ring contacts said second contact portions. 
     
     
       5. The structure of drive section of the power tool according to claim 4, wherein a generatrix of said outer surface of said ring is parallel to the axial direction of said ring, and said each of said second contact portions comprises said curved surface. 
     
     
       6. The structure of drive section of the power tool according to claim 4, wherein, on said outer surface, said ring has said curved surface of which a central part is raised outside to the radial direction of said ring. 
     
     
       7. The structure of drive section of the power tool according to claim 4, wherein said ring is a ball bearing. 
     
     
       8. The structure of drive section of the power tool according to claim 4, wherein said ring is a bearing with spherical outside surface. 
     
     
       9. The structure of drive section of the power tool according to claim 8, wherein said bearing has needle rollers on its inner circumferential surface. 
     
     
       10. The structure of drive section of the power tool according to claim 4, wherein said ring is rotatably attached to said eccentric portion. 
     
     
       11. Structure of drive section of a power tool for giving a swinging motion to a tool .[.such as a sander.]., which comprises: an output shaft portion of a motor having a rotational axis and an eccentric portion deviating from said rotational axis;   a vibratory arm vibratably supported at a predetermined position and holding said tool at its one end; and   connecting section of the other end of said vibratory arm with said eccentric portion formed in shape of two crotches, said eccentric portion and said vibratory arm being connected to each other in such a manner that said eccentric portion is inserted between said two crotches of said vibratory arm, thereby rotational movement of said output shaft portion of said motor being converted into vibrational movement of said vibratory arm, said connecting section having a first contact portion formed on the outer circumferential surface of said eccentric portion and second contact portions respectively formed on the inside surface of each of said two crotches, said second contact portions comprising half pillar like projections of which axes are extended perpendicularly to the axial direction of said vibratory arm, and each of said half pillar like projections contacts said first contact portion, and at least one of said first contact portion and each of said second contact portions comprising a curved surface of which a contour curves on a plane perpendicular to said vibrating axis.   
     
     
       12. Structure of drive section of a power tool for giving a swinging motion to a tool .[.such as a sander.]., which comprises: an output shaft portion of a motor having a rotational axis and an eccentric portion deviating from said rotational axis;   a vibratory arm vibratably supported at a predetermined position and holding said tool at its one end; and   connecting section of the other end of said vibratory arm with said eccentric portion formed in shape of two crotches, said eccentric portion and said vibratory arm being connected to each other in such a manner that said eccentric portion is inserted between said two crotches of said vibratory arm, thereby rotational movement of said output shaft portion of said motor being converted into vibrational movement of said vibratory arm, said connecting section having a first contact portion formed on the outer circumferential surface of said eccentric portion and second contact portions respectively formed on the inside surface of each of said two crotches, said first contact portion comprising an outer circumferential surface of which a central part is raised in its radial direction so as to form said curved surface, and the top of said curved surface contacts said second contact portions, and at least one of said first contact portion and each of said second contact portions comprising a curved surface of which a contour curves on a plane perpendicular to said vibrating axis. .Iadd.13. A power tool comprising:   a housing;   a motor disposed in the housing;   a working member for engaging a workpiece;   a shaft driven by the motor, the shaft having a rotational axis and an eccentric portion offset from the rotational axis; and   an arm driven by the shaft and drivingly connected to the working member, the arm being pivotable about a vibrating axis and having one end formed in the shape of a fork with a pair of prongs, the vibrating axis being generally perpendicular to the rotational axis,   wherein the eccentric portion is received between the pair of prongs such that a first contact portion on the eccentric portion engages a second contact portion on the prongs to convert rotational movement of the shaft about the rotational axis into pivotal movement of the arm about the vibrating axis to pivot the working member about the vibrating axis, and wherein at least one of the first and second contact portions has a curved surface of which a contour curves on a plane generally perpendicular to   
     
     
        the vibrating axis..Iaddend..Iadd.14.  The power tool of claim 13 wherein the second contact portion comprises: a pair of circumferential projections, each circumferential projection being located at a corresponding prong and forming a part of the curved surface with an axis generally parallel to the vibratory axis..Iaddend..Iadd.15. The power tool of claim 13 wherein the first contact portion comprises:   an outer circumferential surface of the eccentric portion, the outer circumferential surface having a radially extended central part to form the curved surface..Iaddend..Iadd.16. The power tool of claim 13 further comprising:   a bearing attached to the eccentric portion, the bearing having an outer circumferential surface forming the first contact surface..Iaddend..Iadd.17. The power tool of claim 16 wherein the bearing outer circumferential surface has a radially extended central part to form the curved surface..Iaddend..Iadd.18. A sander comprising:   a housing;   a motor disposed in the housing;   a working member for holding a piece of sand paper;   a shaft driven by the motor, the shaft having a rotational axis and an eccentric portion offset from the rotational axis; and   an arm driven by the shaft and drivingly connected to the working member, the arm being pivotable about a vibrating axis and having one end formed in the shape of a fork with a pair of prongs, the vibrating axis being generally perpendicular to the rotational axis,   wherein the eccentric portion is received between the pair of prongs such that a first contact portion on the eccentric portion engages a second contact portion on the prongs to convert rotational movement of the shaft about the rotational axis into pivotal movement of the arm about the vibrating axis to pivot the working member about the vibrating axis, and wherein at least one of the first and second contact portions has a curved surface of which a contour curves on a plane generally perpendicular to the vibrating axis..Iaddend..Iadd.19. The sander of claim 18 wherein the second contact portion comprises:   a pair of circumferential projections, each circumferential projection being located at a corresponding prong and forming a part of the curved surface with an axis generally parallel to the vibratory axis..Iaddend..Iadd.20. The sander of claim 18 wherein the first contact portion comprises:   an outer circumferential surface of the eccentric portion, the outer circumferential surface having a radially extended central part to form the curved surface..Iaddend..Iadd.21. The sander of claim 18 further comprising:   a bearing attached to the eccentric portion, the bearing having an outer circumferential surface forming the first contact surface..Iaddend..Iadd.22. The sander of claim 21 wherein the bearing outer circumferential surface has a radially extended central part to form the curved surface..Iaddend..Iadd.23. A drive section for a power tool including a housing, a motor disposed in the housing, and a working member for engaging a workpiece, the drive section comprising:   a shaft driven by the motor, the shaft having a rotational axis and an eccentric portion offset from the rotational axis; and   an arm driven by the shaft and drivingly connected to the working member, the arm being pivotable about a vibrating axis and having one end formed in the shape of a fork with a pair of prongs, the vibrating axis being generally perpendicular to the rotational axis,   wherein the eccentric portion is received between the pair of prongs such that a first contact portion on the eccentric portion engages a second contact portion on the prongs to convert rotational movement of the shaft about the rotational axis into pivotal movement of the arm about the vibrating axis to pivot the working member about the vibrating axis, and wherein at least one of the first and second contact portions has a curved surface of which a contour curves on a plane generally perpendicular to the vibrating axis..Iaddend..Iadd.24. The drive section of claim 23 wherein the second contact portion comprises:   a pair of circumferential projections, each circumferential projection being located at a corresponding prong and forming a part of the curved surface with an axis generally parallel to the vibratory axis..Iaddend..Iadd.25. The drive section of claim 23 wherein the first contact portion comprises:   an outer circumferential surface of the eccentric portion, the outer circumferential surface having a radially extended central part to form   
     
     
        the curved surface..Iaddend..Iadd.26.  The drive section of claim 23 further comprising: a bearing attached to the eccentric portion, the bearing having an outer circumferential surface forming the first contact surface..Iaddend..Iadd.27. The drive section of claim 26 wherein the bearing outer circumferential surface has a radially extended central part to form the curved surface..Iaddend..Iadd.28. A power tool comprising:   a housing;   a motor disposed in the housing;   a working member for engaging a workpiece;   a shaft driven by the motor, the shaft having a rotational axis and an eccentric portion offset from the rotational axis; and   an arm driven by the shaft and drivingly connected to the working member, the arm being pivotable about a vibrating axis and having one end formed in the shape of a fork with a pair of prongs, the vibrating axis being perpendicular to the rotational axis,   wherein the eccentric portion is received between the pair of prongs such that a first contact portion on the eccentric portion engages a second contact portion on the prongs to convert rotational movement of the shaft about the rotational axis into pivotal movement of the arm about the vibrating axis to pivot the working member about the vibrating axis, and wherein at least one of the first and second contact portions has a curved surface of which a contour curves on a plane perpendicular to the vibrating axis..Iaddend.