Low cost limited angle torque dc brushless servomotor and method for fabricating thereof

Abstract

A novel low cost limited angle torque DC brushless servomotor is disclosed. The motor itself is a modified standard low cost DC brush motor which is modified by removing the brush assembly and substituting in its place an appropriately configured multiconductor flexible circuit which is coupled between a controller, the commutator and a magnetic rotor shaft angular displacement sensor. The flexible circuit has a dual function—it provides on one hand the conduit for electrical communication between the controller and the commutator and on the other hand between the sensor and the controller. Part of the circuit is supported between a bearing assembly and the commutator and flexes in consonance with the controlled limited angular rotation of the rotor without affecting performance or reliability of the motor. The rest of the circuit remains stationary during motor operation. The bearing assembly supports the sensor and is used to mount the motor in a housing for a pneumatic servovalve or the like. The sensor comprises a conventional surface mount Hall effect device which on one side is soldered directly to a portion of the flexible circuit and on the other side is glued to the bearing assembly in proximity to a permanent ring-shaped Hall magnet which is fixed concentrically on the rotor shaft. The sensor provides a feedback signal to the controller regarding the angular rotor displacement from a pre-determined null position. The controller compares the feedback signal to an external command signal and drives the rotor (and spool if it is a pneumatic servovalve application) to the commanded position when it detects an error via the flexible circuit.