1. A permanent magnet motor for driving a fan, comprising:
a rotor including a permanent magnet;
a stator including a stator core having a stator winding;
a bearing for rotatably supporting a rotary shaft of said rotor; and
a fan arranged on said rotor;
wherein the fan is rotated while preventing, by a magnetic attraction force of the permanent magnet and the stator core, said rotor moving in a direction of thrust of the rotary shaft with a rotation of said fan; and
wherein a surface magnetic flux density of the permanent magnet facing the stator core is lower at an end portion than at a central portion of the permanent magnet along the direction of thrust of the rotary shaft.
2. A permanent magnet motor according to claim 1, wherein said permanent magnet motor is configured of magnetic materials having different magnetic characteristics so that the surface magnetic flux density of said permanent magnet facing said stator core is lower at the end portion than at the central portion of said permanent magnet along the direction of thrust of said rotary shaft.
3. A permanent magnet motor according to claim 1, wherein a gap between said permanent magnet and said stator is wider at the end portion than at the central portion in the direction of thrust of said rotary shaft in such a manner that the surface magnetic flux density of said permanent magnet facing said stator core is lower at the end portion than at the central portion of said permanent magnet along the direction of thrust of said rotary shaft.
4. A permanent magnet motor according to claim 1, wherein the motor has an internal rotor, the end portion in the direction of thrust of the rotary shaft constituting an outer peripheral portion of the permanent magnet is chamfered or curved in such a maimer that the surface magnetic flux density of said permanent magnet facing said stator core is lower at the end portion than at the central portion of said permanent magnet along the direction of thrust of said rotary shaft.
5. A permanent magnet motor for driving a fan, comprising:
a rotor including a permanent magnet;
a stator including a stator core having a stator winding;
a bearing for rotatably supporting a rotary shaft of said rotor; and
a fan arranged on said rotor;
wherein the fan is rotated while a movement of said rotor in a direction of thrust of the rotary shaft with a rotation of the fan is prevented by a magnetic attraction force of the permanent magnet and the stator core; and
wherein a thickness of the stator core in the direction of thrust of the rotary shaft is greater than a thickness of the permanent magnet in the direction of thrust of the rotary shaft by an amount substantially equivalent to a displacement of said rotor moved by the thrust with a maximum rotational speed of said fan.
6. A permanent magnet motor according to claim 1, wherein a magnetization yoke smaller in thickness than said permanent magnet in the direction of thrust of the rotary shaft is arranged or molded by a die for orientation molding at an end portion of said permanent magnet in such a manner that a surface magnetic flux density of said permanent magnet facing said stator core is lower at the end portion of said permanent magnet than at a central portion along the direction of thrust of said rotary shaft.
7. A permanent magnet motor according to claim 1, wherein said fan is an axial flow fan.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A sheet conveyance apparatus comprising:
a guide unit held in contact with a side end portion of a conveyed sheet to guide the side end portion of the sheet;
a first roller pair arranged on a downstream side of the guide unit, including a driven roller held in contact with a whole sheet in a sheet width direction, and adapted to convey the sheet while pinching the same; and
a second roller pair having a conveyance roller arranged on the downstream side of the roller and adapted to convey the sheet, and a plurality of pinch rollers pinching the sheet in cooperation with the conveyance roller,
wherein each of the plurality of pinch rollers applies to the sheet a conveyance force inclined toward a conveyance path side end which is nearer to the pinch roller, and wherein the smaller the distance between the pinch roller and the conveyance path side end, the greater the inclination of the conveyance force thereof.
2. The sheet conveyance apparatus according to claim 1, wherein each pinch roller is inclined such that the end portion of the pinch roller on the conveyance path side end which is nearer to the pinch roller, is situated on the upstream side from the end portion which is nearer to a center of the conveyance path, and wherein, the smaller the distance to the conveyance path side end, the greater the inclination of the pinch roller.
3. The sheet conveyance apparatus according to claim 1, wherein the guide unit has a first guide abutting a first side end portion of the sheet and a second guide abutting a second side end portion on the opposite side of the first side end portion, wherein there is provided a detection unit detecting the position of the first side end portion, and wherein there is provided a movement unit moving the first guide to a position where it abuts the first side end portion according to the detection result of the detection unit.
4. The sheet conveyance apparatus according to claim 3, wherein the detection unit detects the position of the second side end portion, and wherein the movement unit moves the second guide to a position where it abuts the second side end portion according to the detection result of the detection unit.
5. The sheet conveyance apparatus according to claim 1, wherein the second roller pair has a conveyance force larger than that of the first roller pair.
6. A printing apparatus comprising: a sheet conveyance apparatus as claimed in claim 1; a printing unit arranged on a downstream side of the second roller pair and adapted to form an image on a sheet; and a third roller pair arranged on the downstream side of the second roller pair and in the vicinity of the printing unit and adapted to convey the sheet.
7. The printing apparatus according to claim 6, wherein in the printing unit, a plurality of line type printing heads are arranged along a sheet conveyance direction.