Patent Description:
Embodiments of the present disclosure relate to the field of sensors, and, more particularly, to linear positioning systems for measuring the linear offset of a first object with respect to a second object.

An elevator control system (ECS) is used to stop an elevator car at a desired position at each floor of a building. An ECS typically includes a vertical position sensor that must precisely determine the height of an elevator car with respect to the edge of a floor, regardless of any lateral movements of the elevator car within an elevator shaft. It is desirable, for this purpose that the vertical height of the elevator car be precisely determined with +/- <NUM> positioning error. Typical prior art systems use lasers and mirrors to achieve this accuracy, however, these systems are costly and are prone to variations due to temperature and humidity.

The abstract of <CIT> states: 'A magnetic position sensor including a pair of magnets of opposite polarity which are spaced apart to define an air gap extending along an axis, and a pair of shaped pole pieces at least partially disposed within the air gap and positioned adjacent respective ones of the magnets. The pole pieces are formed of a composite material comprising a non-magnetic material and a magnetizable material. The pole pieces cooperate with the magnets to generate a magnetic field that is substantially symmetrical relative to the axis and which has a magnetic flux density that linearly varies along the axis. A magnetic flux sensor is positioned within the magnetic field to sense varying magnitudes of magnetic flux density along the axis through a sensing plane oriented substantially perpendicular to the axis. The magnetic flux sensor generates an output signal uniquely representative of a sensed magnitude of the magnetic flux density.

The abstract of <CIT> states: An apparatus for determining if an elevator car is level with respect to a landing comprises: a first magnet disposed proximate to the landing; a second magnet disposed proximate to the landing; a sensor for providing a level signal in response to detecting a minimum flux region formed by the first and second magnets; and a processor for determining if the elevator is level with respect to the landing in response to the level signal. Each magnet has a first and second magnetic pole. The first and second magnets are adjacently aligned such that the first magnetic pole of the first magnet is adjacent to the first magnetic pole of the second magnet, and the second magnetic pole of the first magnet is adjacent to the second magnetic pole of the second magnet.

The abstract of <CIT> states: 'A sensing apparatus and sensing device using the sensing apparatus are capable of identifying a relative position of a body which includes a magnetic module by using sensing data of a sensor unit which may be arranged in a <NUM>-dimensional structure.

The disclosure relates to a linear positioning system according to claim <NUM>. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter, whereas the invention is set out in the appended set of claims.

In accordance with the present disclosure, a linear positioning system is specified. In the invention, the system includes a pair of magnets disposed adjacent one another and defining a gap therebetween, and a magnetic sensor movable along an axis passing through the gap.

The linear positioning system of the present disclosure includes a pair of magnets disposed adjacent one another and defining a gap therebetween, the magnets having common poles facing one another, and first, second, and third magnetic sensors disposed within a housing and oriented orthogonally with respect to one another for detecting linear motion along X, Z, and Y axes of a Cartesian coordinate system, respectively, the housing being movable along an axis passing through the gap.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention, however, may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein but to the appended claims. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout.

The present embodiments are generally directed to a linear positioning system (hereinafter "the system") having a stationary portion, shown in <FIG> and a mobile portion, shown in <FIG>. <FIG> shows the stationary portion of the system including a non-magnetic portion <NUM> on which magnets <NUM> are mounted. Non-magnetic portion <NUM> may be a portion of a stationary object or structure, for example, a wall of an elevator shaft or a stationary portion of an elevator assembly. Alternatively, non-magnetic portion <NUM> could be any non-magnetic material on which magnets <NUM> are mounted and which may, in turn, be mounted to the stationary object.

Magnets <NUM> are mounted on the non-magnetic portion <NUM> such as to define a gap <NUM> therebetween. In one preferred embodiment, each of the magnets <NUM> may be approximately <NUM> in width, <NUM> in height, and <NUM> in thickness, while the gap <NUM> may vary between approximately <NUM> and <NUM>. The present disclosure is not limited in this regard. In various embodiments, different sizes of magnets could be used, and different gap sizes are possible. As will be discussed in greater detail below, the response of the system of the present disclosure may vary with the geometry of the magnets <NUM> and the size of the gap <NUM>. In preferred embodiments of the present disclosure, the magnets <NUM> may be formed of neodymium, although other magnetic materials familiar to those of ordinary skill in the art may be used.

<FIG> illustrates the orientation of the poles of the magnets <NUM> (with tips of the illustrated cones indicating the north poles of the magnets <NUM>), wherein common poles of the magnets face one another. In this case, the north poles of the magnets <NUM> face each other, however, in alternate embodiments, the orientations of the magnets <NUM> could be reversed such that their south poles face each other.

<FIG> shows the mobile portion of the system of the present disclosure. The mobile portion may include an arm <NUM> that attaches at a first end to a mobile object or structure such as, for example, an elevator car (not shown). Preferably, arm <NUM> is composed of a non-magnetic material so as not to interfere with the operation of the sensor. A second end of the arm <NUM> may be attached to a housing <NUM> containing three magnetic sensors <NUM>, <NUM>, and <NUM> oriented orthogonally with respect to each other such as to be able to detect linear motion along X, Z, and Y axes, respectively, of a Cartesian coordinate system.

In one embodiment of the system of the present disclosure, only one magnetic sensor (e.g., magnetic sensor <NUM> shown in <FIG>) may be used. For example, in the case where one wishes to detect only the vertical position of an elevator, only one sensor would be required, oriented in the vertical direction. Explanations of the invention below may refer to a single magnetic sensor <NUM> in the housing however (with the sensors <NUM>, <NUM> shown in <FIG> being omitted from such explanations unless otherwise indicated), it should be appreciated by those of ordinary skill in the art that any number of magnetic sensors could be implemented in the system of the present disclosure. Magnetic sensor <NUM> may be, in a preferred embodiment, a Hall effect sensor. In other embodiments any different type of magnetic sensor could be used, for example, TMR or GMR sensors.

Housing <NUM> houses the magnetic sensor <NUM>. Preferably, housing <NUM> is composed of a non-magnetic, or, more preferably, a non-metallic material to prevent blocking of the magnetic field of magnets <NUM> from reaching magnetic sensor <NUM>. The material from which housing <NUM> is made may depend upon the environment in which the sensor is deployed and is preferably configured to protect magnetic sensor <NUM> from large variations in temperature and/or humidity and from vibrations which may affect the position readings. For example, housing <NUM> could be composed of high-density polyethylene (HDPE). The present disclosure is not limited in this regard.

<FIG> shows a top view of the stationary and mobile portions of the system oriented with respect to each other during operation. Housing <NUM> containing magnetic sensor <NUM> may be attached to a moving object which, when in motion, will move along the Z-axis (i.e. into and out of the page in <FIG>) between the magnets <NUM>. In one application of the preferred embodiment, non-magnetic portion <NUM> may be any nonmagnetic material attached to a stationary object, for example, the wall of an elevator shaft. Magnets <NUM> are mounted on non-magnetic portion <NUM>. Arm <NUM> may be attached to the moving object, for example, an elevator car (not shown), and housing <NUM> containing magnetic sensor <NUM> is attached to the arm and adjusted such that it passes, preferably equidistant between magnets <NUM>, as the mobile object moves along the Z-axis. In the case of the elevator example, the Z-axis would be the vertical axis. <FIG> shows a side view the sensor of <FIG>. Preferably, the mobile and stationary objects will be aligned in the desired orientation with respect to each other when magnetic sensor <NUM> (now within view) is equidistant from the top and bottom edges of the magnets <NUM>. For example, the alignment may comprise a floor of an elevator car being aligned with a floor of a building.

<FIG> shows an embodiment of the system of the present disclosure wherein three magnetic sensors <NUM>, <NUM> and <NUM> are implemented within the housing <NUM>. <FIG> shows the axes of the Cartesian coordinate system in the lower left corner, wherein the Z-axis is vertical, the Y-axis horizontal, and the X-axis is into and out of the page. As such, the orientation of the magnetic sensors <NUM>, <NUM>, <NUM> is such that magnetic sensor <NUM> will detect the motion of magnets (e.g., the magnets <NUM>) relative thereto along the X-axis, magnetic sensor <NUM> will detect motion along the Z-axis, and magnetic sensor <NUM> will detect motion along the Y-axis.

<FIG> is a graph showing the vertical displacement of an elevator as the magnetic sensor <NUM> approaches magnets <NUM>, and then departs magnets <NUM> as the elevator ascends or descends. For purposes of an example, assume an elevator car having the magnetic sensor <NUM> mounted thereon is approaching the floor where the magnets <NUM> are mounted from below. As can be seen in the graph, a negative magnetic field is detected when magnetic sensor <NUM> approaches magnets <NUM> from below; a null magnetic field is detected when the magnetic sensor <NUM> reaches the vertical center point of the magnets <NUM>; and a positive magnetic field is detected as the magnetic sensor <NUM> continues ascending past the floor. The opposite circumstance occurs when the elevator car is descending. However, in both cases, when the magnetic sensor <NUM> reaches the vertical center point of the magnets <NUM>, and a null magnetic field is detected, it is assumed that the stationary and mobile objects are aligned. In this case, the positioning of the stationary and mobile components of the system need to be such that when the null magnetic field is detected, the floor of the elevator car is aligned with the floor of the building, preferably with ± <NUM> accuracy.

<FIG> is a graph showing a vertical travel distance of magnetic sensor <NUM> passing through the center of the gap <NUM> between magnets <NUM> for gaps <NUM> (see <FIG>) of various sizes between the magnets <NUM>, wherein the magnets <NUM> are <NUM> in width, <NUM> in height, and <NUM> in thickness. As the size of gap <NUM> becomes smaller, the slope of magnetic fields increases. Certain magnetic sensors require minimum peak to peak magnetic field strength for operation. Depending on such minimum magnetic field strength, the size of the gap <NUM> can be varied to meet such requirement.

<FIG> is a graph showing a vertical travel distance of magnetic sensor <NUM> passing through the center of the gap <NUM> between magnets <NUM> versus the magnetic field measured by the magnetic sensor <NUM>, with magnets <NUM> of varying heights (<NUM>-<NUM>), wherein the magnets <NUM> are <NUM> in width and <NUM> in thickness and wherein the gap <NUM> measures <NUM>. As can be seen, as the height of the magnets <NUM> increases, the slope of the measured magnetic field becomes more linear over a longer vertical travel distance range.

<FIG> is a graph showing a vertical travel distance of magnetic sensor <NUM> passing through the center of the gap <NUM> between magnets <NUM> versus the magnetic field measured by the magnetic sensor <NUM>, with magnets <NUM> of varying widths (<NUM>-<NUM>), wherein the magnets <NUM> are <NUM> in height and <NUM> in thickness and wherein the gap <NUM> measures <NUM>. As can be seen, as the width of the magnets <NUM> increases, the slope of the measured magnetic field increases.

<FIG> is a graph showing a vertical travel distance of magnetic sensor <NUM> passing through the center of the gap <NUM> between magnets <NUM> versus the magnetic field measured by the magnetic sensor <NUM>, with magnets <NUM> of varying thicknesses (<NUM>-<NUM>), wherein the magnets <NUM> are <NUM> in height and <NUM> in width and wherein the gap <NUM> measures <NUM>. As can be seen, thicker magnets <NUM> provide higher sensitivity slopes and larger peak-to-peak signals relative to thinner magnets <NUM>.

<FIG> is a graph showing horizontal travel distances of magnetic sensor <NUM> moving along the X-axis and magnetic sensor <NUM> moving along the Y-axis (see <FIG>) versus magnetic fields measured by the magnetic sensor <NUM> and the magnetic sensor <NUM>, respectively.

The described linear positioning system has the advantage of using a low-cost, dual magnet arrangement, which provides an asymmetric magnetic field across the X, Y, plain. This allows self-canceling of the magnetic variation in the Z direction throughout the operational temperature range of the system. This also allows for a precise measurement along the Z-axis, to sub-<NUM> accuracy, when approaching from either the +Z or -Z directions, and further allows precise measurements, to sub-<NUM> accuracy, throughout the X-Y plane bounded by the magnets <NUM>. Magnetic field contour plots are shown on <FIG>, <FIG>, and <FIG> for magnetic fields measured in the x, y, and z planes (Bx, By and Bz), respectively. The contour plots show linear slopes of Bx, By and Bz when sensors move along the X, Y, and Z directions, respectively.

While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claim(s). Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof. For example, the invention has been described using the example of an elevator car traveling in a vertical direction along a defined Z-axis. The reference to the Z-axis in this case is meant to denote the axis passing between the magnets, and, although described as being vertical in examples herein, one of ordinary skill in the art would realize that this axis could be oriented in any physical direction. It should be further realized that the application of the linear position sensor is not limited to elevators but may be used with any two objects requiring linear positioning and alignment with respect to each other.

Claim 1:
A linear positioning system comprising:
a pair of magnets (<NUM>) disposed adjacent one another along an X-axis of the system and defining a gap (<NUM>) therebetween, each of the magnets having a north pole and a south pole and wherein common poles of the magnets (<NUM>) face one another,
the pair of magnets (<NUM>) being mountable to a stationary structure; and
a magnetic sensor (<NUM>, <NUM>, <NUM>), connectable to a mobile structure, and movable along an axis passing through the gap (<NUM>), wherein, when in use, a null magnetic field is detected by the magnetic sensor (<NUM>, <NUM>, <NUM>) in response to the magnet sensor reaching the vertical point of the magnets (<NUM>) wherein the vertical direction is along a Z- axis defined with respect to the system,
wherein the magnetic sensor comprises a first magnetic sensor (<NUM>), a second magnetic sensor (<NUM>), and a third magnetic sensor (<NUM>), wherein the first, second, and third magnetic sensors (<NUM>, <NUM>, <NUM>) are oriented orthogonally with respect to one another for detecting linear motion along X, Z, and Y axes of a Cartesian coordinate system, respectively.