Abstract: In a dynamic pressure bearing, a dynamic pressure-generating groove is provided to one of a thrust bearing surface and a part of a rotator facing the thrust bearing surface on one of a first and second thrust bearings, and a thrust bearing surface and a part of the rotator on the other one of the first and second thrust bearings which is not provided with the dynamic pressure-generating groove are smoothed so that the smoothed surfaces are formed.

Abstract: A dynamic pressure generating bearing includes a rotational body, a radial bearing provided adjacent to a center of the rotational body to rotatably support the rotational body around the radial bearing and at least one thrust bearing provided on one end of the radial bearing. When the rotational body is stably rotated, a minimum clearance generated between the rotational body and the thrust bearing is always greater than a minimum clearance generated between the rotational body and the radial bearing.

Abstract: A polygon mirror is produced using a diamond tool. The diamond tool includes a major cutting edge and an end cutting edge. The major cutting edge is formed straight by a rake face and a side flank, the major cutting edge having a first side and a second side. The end cutting edge is formed straight by the rake face and a front flank, the end cutting edge having a third side. A microscopic cutting edge is arranged between the second side and the third side so that the major cutting edge and the microscopic cutting edge together create a first corner at the second side, and the end cutting edge and the microscopic cutting edge create a second corner at the third side. The rake face is inclined downward from the second corner to the first side. The microscopic cutting edge is between 0.1 mm and 0.4 mm in a direction of the end cutting edge. The microscopic cutting edge at the first corner is swept back by an amount between 0.21 .mu.m and 0.6 .mu.

Abstract: A trip throttle valve with a manual exerciser and combination of a hydraulic piston and a biasing force bearing sleeve is provided in place of a piston. The piston is not directly connected to a valve stem and the sleeve is threadably engaged with the valve stem so as to cause relative axial movement between the sleeve and the valve stem when the stem is rotated through the manual exerciser. The hydraulic portion of the valve is provided with a by-pass passage so that the piston is made axially movable toward the sleeve under the pressure which occurs when the by-pass passage for the hydraulic liquid is blocked but the piston is arrested at a certain axial position where the by-pass passage is still blocked and the axial movement of the sleeve is restricted against the piston.