The present invention relates generally to position sensors and methods of determining the positions between two relatively-movable members, and, more particularly, to an improved non-contacting magnetically-operated position sensor for sensing and determining the position between two relatively-movable members, and to an improved method of determining the position between such members.
There are many applications in which it is necessary to determine the position between two relatively-movable members.
In some applications, it would be highly desirable to determine such position without introducing friction between the members.
In still other applications, it would be desirable to provide such a position detector that is relatively insensitive to vibrations and the like.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved non-contacting magnetically-operated position sensor for sensing and determining the position between two relatively-movable members, and to an improved method of determining the position between two relatively-movable members.
The improved position sensor (20) broadly comprises: a pair of flux-conductive converging polepieces (21, 22) mounted on one of the members (23), the polepieces having convergent ends (24, 25) and divergent ends (26, 28); a magnetic sensor (29) mounted on the one member and positioned proximate one of the ends of the polepieces, the magnetic sensor being adapted to produce an output signal as a function of the magnetic flux density therein; and a magnet (30) mounted on the other of the members for movement toward and away from the magnetic sensor, the magnet being positioned between the polepieces to define a first air gap (32) between the magnet and a first of the polepieces and a second air gap (33) between the magnet and a second of the polepieces; the reluctances (RV1 and RV2, respectively) of the first and second air gaps (32, 33, respectively) varying as a function of the position of the magnet relative to the magnetic sensor; whereby the sensor output signal will be a function of the position of the magnet from the magnetic sensor, which causes the lengths of air gaps RV1 and RV2 to change.
The sum of the reluctances of the first and second air gaps is a constant at any position of the magnet relative to the magnetic sensor.
In one form, the polepieces are positioned symmetrically about an axis (x-x), and the magnet moves substantially along the axis. Hence, the reluctances of the first and second air gaps are substantially equal at all permitted positions of the magnet relative to the magnetic sensor.
The magnet may be mounted for linear or rotary movement relative to the magnetic sensor. If mounted for rotary movement, the polepieces may be helically wound on the one member.
The magnetic sensor may be a Hall effect sensor, a magneto-resistive sensor, or some other sensor.
In one form, the transverse cross-section of each polepiece is substantially constant along its entire operative length, and may be substantially rectangular. In another form, the transverse cross-sections of the polepieces are shaped along their lengths such that the magnetic sensor output signal varies substantially linearly with the position of the magnet from the magnetic sensor.
The magnet and the first and second air gaps may be arranged magnetically in series with the magnetic sensor. The magnet may be formed of a rare earth material, or any high coercive force magnet material.
The position sensor may further include: a first stop (34) for limiting movement of the magnet toward the magnetic sensor, and a second stop (35) for limiting movement of the magnet away from the magnetic sensor.
The magnetic sensor (29) is preferably positioned between the convergent ends (24, 25) of the polepieces.
The improved method broadly includes the steps of: mounting a magnet (30) on one of the members (31); mounting a magnetic sensor (29) on the other of the members (23), the magnetic sensor being adapted to produce an output signal as a function of the magnetic flux density therein; mounting a flux-conductive first polepiece (21) on the other member (23) so as to define a first air gap (32) between the magnet and the first polepiece, the length of the first air gap varying with the distance between the magnet and the magnetic sensor; and mounting a flux-conductive second polepiece (22) on the other member so as to define a second air gap (33) between the magnet and the second pole-piece, the length of the second air gap varying with the distance between the magnet and the magnetic sensor; thereby to provide a magnetic circuit in which the magnet, the magnetic sensor and the air gaps are arranged in series such that the output signal of the magnetic sensor will be a function of the distance between the magnet and the magnetic sensor, which causes the variable-reluctance air gaps (RV1 and RV2) to change.
With this method, the polepieces may be so configured and arranged that the output signal varies substantially linearly with the distance between the magnet and the magnetic sensor.
Accordingly, the general object of this invention is to provide an improved non-contacting position sensor for sensing and determining the position of two relatively-movable members.
Another object is to provide and improved method of determining the position between two relatively-movable members.
These and other objects and advantages will become apparent from the foregoing an ongoing written specification, the drawings and the appended claims.
At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.
Referring now to the drawings, and, more particularly, to
A magnetic sensor 29, such as a Hall effect sensor, a magneto-resistive sensor or the like, is mounted on member 23 and is adapted to produce an output signal as a function of the magnetic flux density therein.
A magnet 30 is mounted on another member 31 that is movable relative to member 30. In
The sum of the reluctances of the first and second air gaps is a constant at any position of the magnet relative to the motor, regardless of whether the magnet is generally centered between the polepieces or not. If axis x-x bisects the angle of convergence of the polepieces, then the sum of the reluctances of the first and second air gaps 32, 33 will be substantially the same, assuming that each polepiece has a constant transverse cross-section and composition.
In another aspect, the invention provides an improved method of determining the position between two relatively-movable members 23, 31, which comprises the steps of: mounting the magnet 30 on one of the members 31; mounting a magnetic sensor 29 on the other of the members 23, the magnetic sensor being adapted to produce an output signal as a function of the magnetic flux density therein; mounting a flux-conductive first polepiece 21 on the other member 23 so as to define a first air gap 32 between the magnet and the first polepiece, the length of the first air gap varying with the distance between the magnet and the magnetic sensor; and mounting the flux-conductive second polepiece 22 on the other member so as to define a second air gap 33 between the magnet and the second polepiece, the length of this second air gap varying with the distance between the magnet and the magnetic sensor; thereby to provide a magnetic circuit in which the magnet, the magnetic sensor and the air gaps are arranged in series such that the output signal of the magnetic sensor will be a function of the distance between the magnet and the magnetic sensor.
While the curve shown in
The present invention expressly contemplates that many changes and modifications may be made. For example, the particular material of which the polepieces are constructed is not deemed critical, and may be changed. As indicated above, the cross-section of the polepieces may be changed along their longitudinal extents so as to linearize the output signal. The magnetic may be a rare earth material, such as samarium cobalt. However, such magnetic may be of other forms as well. The magnetic sensor may be a Hall effect position sensor, a magneto-resistive element, or some other element responsive to the magnitude of the magnetic flux therein.
Therefore, while a presently-preferred form of the improved position sensor has been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.