Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1996-12-27
1998-07-28
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 36, 335276, 335279, H02K 720, H02K 3300
Patent
active
057866490
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a rotary electromagnetic actuator. More particularly, the invention relates to an improved Rotary Electromagnetic Actuator suitable for, but not limited to, actuating rotary valves.
Rotary electromagnetic actuators are presently used in a variety of industrial and scientific applications. Examples of such applications include automatic liquid dispensing devices and fuel regulators. Some examples of known electromagnetic actuators are shown in GB1461397 (C.A.V. Limited), GB275942 (General Railway Signal Company), US5337030 (Mohler) and WO90/02870 (Robert Bosch GmbH).
The actuator shown in GB1461397 contains a shaft rotatably mounted between the pole pieces of an electromagnet. A rotor member is attached to the shaft and is shaped such that when a current is applied to the coil, the shaft will tend to rotate to a position of least reluctance. It is not clear from the '397 patent what will happen when current stops being applied to the coil.
GB275942 shows an electromagnetic actuator used in railway signalling devices. FIG. 5 of the patent, and the related text, disclose a shaft having a first electromagnetic coil wound around it. A shaped rotor member is attached to the shaft and a stator member is also provided. A second electromagnetic coil acts to magnetize the stator member when energised. When the first coil is also supplied with current, the shaft will tend to rotate until a position of least reluctance is reached. When the current supply to the first coil ceases, the shaft will rotate back to the starting position. The device of the '942 patent therefore operates to rotate the shaft forward to a particular position and then allow it to fall back again. US5337030 shows a permanent magnet brushless torque actuator. A rotatable shaft carries a rotor with an even number of magnetised regions, adjacent regions being permanently magnetised in opposite directions. An electromagnetic assembly is shown arranged so that energisation of the electromagnet assembly causes the shaft to tend to a position where the permanent magnetic regions are aligned with the magnetisation of the electromagnet assembly. A spring is shown which biases the rotor to its zero position when the electromagnet is not energised, the shaft being free to rotate in either direction upon energisation. However, work must continually be done to overcome the biasing force of the spring. If the spring is not used, a complicated and costly feedback position sensing means is proposed. Furthermore, unidirectional rotation is not ensured.
W090/02870 discloses an electric rotatory actuator having a shaped rotor with two regions which are permanently magnetised in opposite directions, rotating within the shaped arms of an electromagnetic stator member. When a coil associated with the stator member is energised, the rotor rotates to a particular position, determined by the amount of current. When no current is supplied, the actuator rotates back to its zero position; rotation of the shaft is therefore not unidirectional. Furthermore, the variable air gap in the device results in a torque which is not constant.
None of the prior art devices shows a device which rotates unidirectionally in a defined way on each actuation. Furthermore, the prior art devices, in order to define the direction of rotation must either have a spring means against which the device is continually having to work, or complicated feedback means, or alternatively a variable air gap resulting in non-constant torque.
It is an object of the present invention to overcome the above disadvantages. Specifically it is an object of the present invention to provide a unidirectionally rotating electromagnetic actuator which is efficient and precisely controllable, while being simple, reliable and inexpensive to manufacture. It is a further object of the invention to provide a rotary electromagnetic actuator which rotates through a defined angle in an accurate, reproducible manner with a high torque. It is a still further object of the invention to provide a rot
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Dougherty Thomas M.
Wallace, Jr. Michael J.
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