Combined position sensor and magnetic motor or bearing

• US 4,652,820 A
• Filed: 03/23/1983
• Issued: 03/24/1987
• Est. Priority Date: 03/23/1983
• Status: Expired due to Fees

• Current Assignee: North American Philips Corp. (Koninklijke Philips N.V.)
• Original Assignee: North American Philips Corp. (Koninklijke Philips N.V.)
• Inventors: Maresca, Robert L.
• Primary Examiner(s): Karlsen, Ernest F.
• Assistant Examiner(s): Snow, Walter E.
• Application Number:
  US06/478,171
• Time in Patent Office: 1,462 Days
• Field of Search: 324/207, 324/208, 324/232, 324/225, 361/143, 308/10, 104/284, 318/652, 318/653
• US Class Current: 324/207.16
• CPC Class Codes: F16C 32/0448 by using the electromagnet itself as sensor, e.g. sensorless magnetic bearings
• CPC Class Codes: F16C 32/0459 Details of the magnetic circuit
• CPC Class Codes: G01B 7/02 for measuring length, width or thickness G01B7/004, G01B7/12 take precedence
• CPC Class Codes: G01N 29/30 Arrangements for calibrating or comparing, e.g. with standard objects
• CPC Class Codes: H01F 7/08 with armatures
• CPC Class Codes: H02K 29/12 using detecting coils using the machine windings as detecting coil

Abstract

A combined magnetic sensor and actuator device for applying a magnetic force to a magnetizable body and for sensing the distance between the device and the magnetizable body. The device includes a magnetizable pole piece separated from the magnetizable body by gaps. The pole piece, gaps, and magnetizable body form a magnetic circuit with the gaps preferably being the major reluctance of the circuit. Separate means are provided for generating a relatively large time-varying magnetic actuating flux in the magnetic circuit and for generating a relatively small time-varying magnetic sensing flux in the magnetic circuit. Each magnetic flux follows a flux path, such that the two flux paths have at least a portion in common. Detection means measure the relatively small magnetic flux in the magnetic circuit, and thereby measure the distance between the device and the magnetizable body.

Claims

1. A magnetic sensor and actuator device for applying a magnetic force to a magnetizable body and for sensing the distance between the device and the magnetizable body, said device comprising:

a magnetizable pole piece projecting toward the magnetizable body and separated therefrom by gaps, said pole piece, gaps, and magnetizable body forming a magnetic circuit, the gaps being the major reluctance of the magnetic circuit;

first means for generating a relatively large and relatively low frequency time-varying magnetic actuating flux in the magnetic circuit, said flux following a first flux path;

second means for generating a relatively small and relatively high frequency time-varying magnetic sensing flux in the magnetic circuit, said flux following a second flux path having at least a portion in common with the first flux path; and

detection mans for measuring the relatively small, relatively high frequency magnetic flux in the magnetic circuit;

characterized in that;

the first magnetic flux-generating means further comprises an electrical conductor wound around the pole piece to form a coil and means for generating a relatively low frequency electric current in the coil, said low frequency electric current being a drive signal;

the second magnetic flux-generating means further comprises an electrical conductor wound around the pole piece to form a coil and means for generating a relatively high frequency electric current in the coil;

the detection means generates a position signal indicating the relative distance between the pole piece and the magnetizable body; and

the device further comprises negative feedback-control means which compare a reference signal to the position signal to generate the driving signal.

2. A device as claimed in claim 1, characterized in that the gaps are the major reluctance of the magnetic circuit.

3. A device as claimed in claim 2, characterized in that the first and second flux paths are identical.

4. A device as claimed in claim 3, characterized in that:

the first magnetic flux-generating means generates a relatively low frequency magnetic flux;

the second magnetic flux-generating means generates a relatively high frequency magnetic flux; and

the detection means measures the high frequency magnetic flux in the magnetic circuit.

5. A device as claimed in claim 4, characterized in that the detection means measures the amplitude of the high frequency magnetic flux.

6. A device as claimed in claim 4, characterized in that the detection means measures the phase of the high frequency magnetic flux.

7. A device as claimed in claim 4, characterized in that the pole piece and the magnetizable body are made of soft-magnetic materials.

8. A device as claimed in claim 7, characterized in that the pole piece and the magnetizable body are made of ferrites.

9. A device as claimed in claim 4, characterized in that the pole piece is "U"-shaped.

10. A device as claimed in claim 9, characterized in that the gaps comprise at least 95% of the total reluctance of the magnetic circuit.

11. A device as claimed in claim 10, characterized in that the first and second magnetic flux-generating means comprise a single electrical conductor wound around the pole piece to form a coil.

12. A device as claimed in claim 11, characterized in that:

the first magnetic flux-generating means further comprises means for generating a relatively low frequency electric current component in the coil; and

the second magnetic flux-generating means further comprises means for generating a relatively high frequency electric current component in the coil.

13. A device as claimed in claim 12, characterized in that the detection means comprises a high-pass filter for separating the high frequency electric current component from the low frequency component.

14. A device as claimed in claim 13, characterized in that the high-pass filter is a notch filter.

15. A device as claimed in claim 14, characterized in that the detection means further comprises means for measuring the amplitude of the high frequency electric current component.

16. A device as claimed in claim 14, characterized in that the detection means further comprises means for measuring the phase of the high frequency electric current component.

17. A magnetic sensor and actuator device for applying a magnetic force to a magnetizable body and for sensing the distance between the device and the magnetizable body, said device comprising:

a magnetizable pole piece projecting toward the magnetizable body and separated therefrom by gaps, said pole piece, gaps, and magnetizable body forming a magnetic circuit, the gaps being the major reluctance of the magnetic circuit;

first means for generating a relatively large and relatively low frequency time-varying magnetic actuating flux in the magnetic circuit, said flux following a first flux path;

second means for generating a relatively small and relatively high frequency time-varying magnetic sensing flux in the magnetic circuit, said flux following a second flux path having at least a portion in common with the first flux path; and

detection means for measuring the relatively small, relatively high frequency magnetic flux in the magnetic circuit;

characterized in that;

the first and second magnetic flux-generating means comprise a single electrical conductor wound around the pole piece to form a coil;

the first magnetic flux-generating means further comprises means for generating a relatively low frequency electric current component in the coil, said low frequency electric current component being a drive signal;

the second magnetic flux-generating means further comprises means for generating a relatively high frequency electric current component in the coil;

the detection means comprises a high-pass filter for separating the high frequency electric current componet from the low frequency component, said detection means generating a position signal indicating the relative distance between the pole piece and the magnetizable body; and

the device further comprises negative feedback-control means which compare a reference signal to the position signal to generate the driving signal.

18. A magnetic sensor and actuator devices for applying a magnetic force to a magnetizable body and for sensing the distance between the device and the magnetizable body, said device comprising:

a magnetizable pole piece projecting toward the magnetizable body and separated therefrom by gaps, said pole piece, gaps, and magnetizable body forming a magnetic circuit, the gaps being the major reluctance of the magnetic circuit;

first means for generating a relatively large and relatively low frequency time-varying magnetic actuating flux in the magnetic circuit, said flux following a first flux path;

second means for generating relatively small and relatively high frequency time-varying magnetic sensing flux in the magnetic circuit, said flux following a second flux path having at least a portion in common with the first flux path; and

detection means for measuring the relatively small, relatively high frequency magnetic flux in the magnetic circuit;

characterized in that the pole piece has three legs and an "E"-shaped cross-section, one of the legs being shorter than the other two, the shorter leg also having an end with a smaller cross-section than the other two legs.

19. A device as claimed in claim 18, characterized in that the device is a magnetic bearing for suspending the magnetizable body.