Abstract: An electromagnetic clutch according to the invention includes a first rotatable member having an axial end plate of magnetic material and a second rotatable member. The second rotatable member includes a drive shaft, and a hub mounted on an end of the shaft. An annular armature plate is disposed on an outer peripheral portion of the hub facing the axial end plate of the first rotatable member with an axial air gap therebetween. An electromagnetic device is disposed within the first rotatable member for attracting the armature plate to the axial end surface of the first rotatable member. The armature plate is elastically connected with the hub by a plurality of leaf springs and is made of materials with a low Curie point. Meltable elements are disposed on the armature plate to define the axial air gap between the first rotatable member and the armature plate.

Abstract: An electromagnetic clutch includes a clutch rotor and an annular electromagnet. The clutch rotor has a rotor which sectional side view is a U-shaped configuration and a pulley mounted at an outer peripheral surface of the rotor. The annular electromagnet is disposed in an annular cavity of the rotor. An armature plate facing to a front end surface of the rotor is supported elastically by a stopper plate through a plurality of leaf springs. The stopper plate is fixed to an outer end of a drive shaft. First engaging elements are formed at an outer peripheral surface of the rotor. Second engaging elements are formed at an inner peripheral surface of the pulley. The first and second engaging elements are complementary and prevent the relative rotational motion of the pulley and the rotor when engaged. A stopper provided on the outer peripheral surface of the rotor prevents the relative axial movement of the pulley and the rotor.

Abstract: A photographic lens comprising, from front to rear, a first lens unit of positive power, a stop, a second lens unit of positive power, a third lens unit of negative power and a fourth lens unit of positive power. The first lens unit has at least one negative lens having a strong concave surface facing the stop, and the second lens unit has at least one negative lens having a strong concave surface facing the stop. When focusing is performed from an infinitely distant object to a close object, the first and second lens units are moved forward in unison, while the third lens unit is moved by a less amount than the amount of movement of the first and second lens units, whereby closeup optical performance is improved.

Abstract: A zoom lens including, from front to rear, a first lens unit of positive power, a second lens unit of negative power and a third lens unit of positive power, wherein for a standard focal length range at least the first and second lens units move simultaneously and independently of each other, and to obtain a focal length beyond the standard range, at least the second lens unit moves, whereby the locus of movement of the first lens unit bends at an end of the standard range, and as the standard range is exceeded, the first lens unit either remains stationary or moves forward.

Abstract: A zoom lens comprising, from front to rear, a first zoom section and a second zoom section, the first zoom section having a plurality of movable lens units which simultaneously move to effect zooming, and the second zoom section having a plurality of axially movable lens units, the light beam exiting from the rearmost unit in the first section enters directly the frontmost unit in the second section, and the refractive powers of the front and rear lens units are made positive and negative respectively, whereby the front and rear lens units are simultaneously moved in such a way that the magnifying power of the rear lens unit remains positive when the focal length of the entire system varies.

Abstract: An electromagnetic clutch is disclosed that includes a pulley and an electromagnetic mechanism. A hub is secured on a drive shaft and has a radially extending flange portion. An armature plate is concentrically disposed on the hub and faces the axial end surface of the pulley with an axial air gap therebetween. A holder plate is fixed on an outer axial end surface of the armature plate and is formed with a triangularly axially extending flange. The radial flange portion of the hub is also formed with a second axially extending flange corresponding to the first flange. The first and second axially extending flanges are formed of a similar configuration and face one another with a radial gap. An elastic member is disposed in the radial gap to ease the impact force created when the clutch is engaged.

Abstract: A photographic lens comprising four lens units, of which the first and second counting from front are of positive power, and the third and fourth have powers of opposite sign to each other, wherein as focusing is performed from infinitely distant object to nearby object, the first three units are axially moved in such differential relation that all the three air separations between the successive two units increase, while the fourth lens unit is held stationary during focusing, thereby the picture quality for the nearby object is greatly improved.

Abstract: An electromagnetic clutch according to the invention includes a first rotatable member having an axial end plate of magnetic material and a second rotatable member. The second rotatable member includes a drive shaft, and a hub mounted on an end of the shaft. An annular armature plate is disposed on an outer peripheral portion of the hub facing the axial end plate of the first rotatable member with an axial air gap therebetween. An electromagnetic device is disposed within the first rotatable member for attracting the armature plate to the axial end surface of the first rotatable member. The armature plate is elastically connected with the hub by a plurality of leaf springs. A self-return type temperature switch is fixedly disposed within the first rotatable member and closely placed to the axial end plate of the first rotatable member for controlling the energization of the electromagnetic device according to the temperature on the axial end plate.

Abstract: A zoom lens having a plurality of lens units with the air separations, at least one of which is varied to effect zooming, the rearmost lens surface of successive two of the lens units and the frontmost lens surface of the rear one being both formed to convex shapes toward the front, whereby when these two lens units axially move at different speeds from each other, a soft-focus effect of varying magnitude is produced on the image.

Abstract: A zoom lens whose first lens group, counting from front, has a negative refractive power and moves axially in differential relation to a following lens group to effect zooming, wherein the first lens group is constructed with a lens unit of negative power followed by another lens unit of positive power, whereby for focusing purposes, the negative lens unit is axially moved, while the positive lens unit is held stationary, to improve the stabilization of aberration correction throughout the entire focusing range.

Abstract: A zoom lens including, from front to rear, a first lens unit of negative power and a second lens unit of positive power with the separation therebetween being varied to effect zooming. The first lens unit is moved to effect focusing, wherein with the first lens unit focusing a finite object distance on the wide angle side, the second lens unit moves rearward to obtain focal lengths beyond the zooming range.

Abstract: A molten metal discharging device comprising:a stationary plate adapted to be mounted at a bottom portion of a container accomodating molten metal, the stationary plate having a molten metal passage bore for permitting the molten metal from the container to be discharged therethrough, anda slide plate slidable along a lower face of the stationary plate and adapted to open or close the passage bore by being slidably displaced relative to the stationary plate, in whicha circumferential wall of the passage bore in the stationary plate is made of dense refractory material and the circumferential wall made of the dense refractory material has a plurality of gas supply holes therein for permitting a gas to be supplied into the passage borehas less fear that the passage bore thereof may be blocked by the solidification of the molten metal and/or deposition of metal oxides and has an improved resistance against corrosion by the molten metal.

Abstract: An electromagnetic clutch is disclosed which includes a pulley and an electromagnetic coil. A hub is secured on a drive shaft and has a radially extending flange portion which faces the pulley at a predetermined axial gap. An armature plate is disposed in the axial gap between the pulley and the radially extending flange portion of the hub. The armature plate is elastically connected to the flange portion of the hub by a plurality of spring members. The spring members are provided with a pair of fittings radially opposed to one another at a predetermined radial gap to prevent excessive bending of the spring members during initial operation of the electromagnetic clutch. When the armature plate beings to rotate, each spring member bends to reduce the gap between the pair of radially opposed fittings to thereby absorb the impact force.

Abstract: A molten metal discharging device including a stationary plate of refractory material and adapted to be mounted at a bottom portion of a container for accommodating molten metal, the stationary plate having a molten metal passage bore for permitting the molten metal from the container to be discharged therethrough, and a slide plate of refractory material slidable along a lower face of the stationary plate and adapted to open or close the passage bore by being slidably displaced relative to the stationary plate, wherein the stationary plate includes a stationary plate main body having the passage bore therein, at least a major part of the main body being made of porous refractory material, the stationary plate main body having a chamber around a circumferential wall part of the passage bore and a gas introduction hole communicated with the chamber for introducing a gas from outside into the chamber, the circumferential wall part having gas supply hole elements for supplying the gas therethrough from the chamb

Abstract: A method of making a clutch rotor for use in an electromagnetic clutch according to this invention includes the steps of forming a cup-shaped blank with a generally cylindrical annular flange wall; applying an outward transaxial force to the annular flange wall of the cup-shaped blank to form an annular outward bulge in the flange wall forming at least one inwardly projecting approximately V-shaped groove in the annular bulge by a press operation; applying a roller working operation to the approximately V-shaped groove to form the final V-shaped groove; and pressing a portion of the bottom plate to form an inner cylindrical member.