The present invention relates to an electromagnetically driven device and, more particularly, to an improvement of the device.
A typical electromagnetically driven device is a solenoid device having a coil and a plunger. The coil produces a magnetic force when current flows through the coil. Preferably, the coil is provided with an armature which can be magnetized when the coil is energized to produce a magnetic force. The plunger includes a rod member and a segment made of magnetic material rigidly attached to one end of the rod. The rod member is movably inserted into the coil in the axial direction of the coil while the segment is positioned adjacent to the armature with a predetermined gap therebetween. When the current flows through the coil, the armature is magnetized for generating a magnetic force which attracts the segment. Thus, the segment is moved towards the armature together with the plunger rod. The movement of the rod acts on a mechanical device provided adjacent to the rod member.
In the solenoid device described above, the magnetic force generated from the armature is exponentially reduced from the outside face of the armature towards the axial direction of the coil. Accordingly, when the gap between the armature and the segment is considerably large, the magnetized armature attracts the segment with a weak attractive force. Therefore, the solenoid device described above may be applicable only to a mechanical device which requires a short distance of movement of the plunger. However, in the case where the plunger is required to move a considerably long distance with quick and stable motion, it is necessary to strengthen the attractive force between the coil and the plunger. For this purpose, many improvements have been made.
One example is disclosed in U.S. Pat. No. 4,060,313 to Kondo issued on Nov. 29, 1977. Kondo discloses a coil and a blade inserted in the coil shiftably in an axial direction of the coil. A magnet sheet is mounted in the blade inside the coil so that the magnetic force developed in the coil is exerted on the magnet sheet to move it together with the blade. In this example, the stroke of the magnet is determined by the axial length of both the magnet and the coil, thus the size of the device becomes large as the stroke of the blade becomes longer. Furthermore, the magnet can be disadvantageously trapped at the center of the coil. If the magnet is made long for increasing the length of stroke, the magnetic resistance is increased. Then, it requires an increase in current in the coil for increasing the magnetic force.
A similar electromagnetic driven device is disclosed in U.S. Pat. No. 4,072,965, to Kondo issued on Feb. 7, 1978.
Another electromagnetically driven device is a linear motor having an array of magnets aligned and fixed on a base and a movable member positioned above and close to the magnet array with a predetermined gap. The movable member is provided with at least one coil for producing a magnetic force. The produced magnetic force attracts the magnet array and advances the movable member. This device requires the supply of electricity to the coil in the movable member. Therefore, the wiring or connection between the power source and the coil is complicated.