1. Field of the Invention
The present invention relates to a system for preventing malfunction of a switching circuit for a linear motor, and more particularly to a system for preventing malfunction of a switching circuit for a linear motor capable of preventing malfunction of the switching circuit due to magnet flux generated from permanent magnets mounted on a movable element.
2. Description of the Conventional Art
Linear motors are, generally, used in accurate transfer control of objects, such as machining tools, industrial robots, etc.
A conventional linear motor, shown in FIGS. 1 and 2, is comprised of a stator element 1 and a movable element 2. The stator element 1 has plural armature coils 3 arranged in a longitudinal direction of the stator element 1, and the movable element 2 has a plurality of permanent magnets 4 provided opposing to the plural armature coils 3. A plurality of permanent magnets 4 disposed to face the plural armature coils 3 are arranged to have their polarities of N pole and S poles separated to each other.
When electric current flows to the plural armature coils 3, the linear motor generates a thrust allowing the movable element 2 to be moved, by Fleming.quadrature.s left-hand rule. To create such a thrust able to move the movable element 2, the current flows into the armature coil 3 should be controlled. At this time, the current flowing into the armature coil 3 may be controlled using plural Hall sensors 6 mounted on the stator element 1.
On the other hand, the plural Hall sensors 6 output a constant level of voltage when the sensors 6 sense magnetic flux created from the sensing magnet 5 mounted on the movable element 2. The output voltage is used for controlling switches (not shown) employed to control the current flows into the armature coils 3. With the controlled current flows into the armature coils 3 by the turning ON/OFF of the switches, the thrust for moving the movable element 2 can be generated.
While the use of the sensing magnets coupled to the movable element 2 are needed to control the ON/OFF of the switches, malfunction of a switching circuit may occur due to relatively stronger intensity of magnet flux generated from the permanent magnets of the movable element 2.
To prevent such an occurrence, a dummy magnet (not shown), independently of the generation of the thrust, mounted on both sides of the movable element 2, is employed to prevent malfunction of the switching circuit 20 which may be caused by the magnet flux from the permanent magnet 4. In case such a dummy magnet is used so as to prevent abnormal operation of the Hall sensor 6, the weight of the movable element 2 increases, which requires to design the linear motor capable of producing higher thrust.