Patent Application
20180003525
Many endeavors call for measuring a position of one object relative to another. Measuring the linear movement of one object relative to another may also be desirable in a great variety of situations. One mechanism capable of measuring such positioning or linear movement is known as a linear variable differential transformer (LVDT). LVDTs generally operate by driving an electrical current through a primary solenoid coil that may cause an induction current to be generated in secondary solenoid coils disposed axially on either side of the primary coil. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, may slide along an axis between the primary and secondary coils and alter the induced current as it moves. When the core is displaced toward one of the secondary coils, the voltage in that secondary coil may increase as the voltage in the other secondary coil decreases and vice versa. While this design may have a variety of advantages, the length that may be measured may be limited given that it is the proximity to edges of the core the causes the induced currents to rise and fall.
Another mechanism for measuring linear displacement, having a longer possible stroke than previously described LVDTs, may comprise a tube with ferromagnetic ball bearings disposed therein. This series of ball bearings may act as a scale around which a plurality of coils may pass. As in a traditional LVDT, an electrical current may be driven through one of the coils while a number of other spaced pickup coils detect variations in induced magnetic fields. However, in this case, the ball bearings may create a repeating differentiation in the induced magnetic fields. While this design may allow for longer measurement stroke, it still requires coils of wire spaced around a center, just like traditional LVDTs, which may add to its size, complexity, cost and structural weakness.
Thus, while conventional LVDTs and other known linear position sensors have many advantages, a linear measurement device comprising fewer parts, more robust construction, smaller size, simplified circuitry, or reduced cost may be desirable. Further, while conventional LVDTs may require alternating current that may draw significant power, a linear measurement device with reduced power demands may be desirable. Additionally, the relatively short measurement stroke of conventional LVDTs often requires a scaling of the measured signals. A linear measurement device comprising a longer stroke may not require such scaling and, thus, may be desirable.
A relatively small linear measurement device may comprise few working parts, a robust construction and simple electrical circuitry. Such a linear measurement device may be formed from a first tube axially translatable with respect to a second tube. Inside the first tube may be placed a sensor capable of sensing a magnetic field. A magnet may also be found within the first tube and produce a magnetic field sensible by the sensor. The second tube may comprise a plurality of deviations disposed therealong capable of altering the magnetic field when near the magnet. As the first tube is axially translated with respect to the second tube, the sensor may sense alterations in the magnetic field due to the plurality of deviations thus allowing for a linear displacement to be determined.
The magnet 102 may produce a magnetic field 106 capable of being sensed by the sensor 103. Further, the second tube 110 may comprise a plurality of deviations 111 disposed thereon capable of altering the magnetic field 106 when in proximity thereto. Not only may the sensor 103 sense the magnetic field 106, but it may also be capable of sensing alterations in the magnetic field 106 due to the deviations 111. Additionally, while the present embodiment shows the sensor 103 positioned axially adjacent the magnet 102, such sensors could also be placed in various positions, such as off axis, relative to magnets based on where they are likely to experience substantial changes in magnetic field due to interactions with a second tube. Further, if deviations disposed on a second tube are not symmetric about an axis thereof then it may be advantageous to specifically orient such sensors in relation to the deviations.
The second tube 110 may be formed of a material comprising a relative permeability significantly greater than unity. As such, physical variations in a sidewall 112 of the second tube 110 may form the plurality of deviations 111. For example, in the embodiment shown, the plurality of deviations 111 may comprise a plurality of holes 113 disposed in the sidewall 112 of the second tube 110. As shown, the plurality of holes 113 may each be substantially identical in shape and evenly spaced axially along the second tube 110. This plurality of holes 113 may be formed by any of a variety of machining or cutting methods. While such a configuration may be desirable in many situations due to its axial consistency, other embodiments comprising uneven configurations could provide a variation in resolution along the displacement.
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The circuit board 104 may comprise electronics capable of interpreting data from the sensors and calculating linear displacement of the first tube 101 relative to the second tube 110. The electronics may further comprise a counter capable of counting repetitive magnetic field alterations sensed by the sensors. A wire 116 extending from the circuit board 104 along the first tube 101 may electrically connect the sensors to further electronics outside the first tube 101.
In addition, while the present embodiment shows magnets and sensors disposed within an inner tube and magnetic field altering deviations disposed on an outer tube, a reverse configuration comprising magnets and sensors on an outer tube and deviations on an inner tube may function similarly.
Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.
