INDUCTANCE COIL SENSOR

Abstract: The accurate detection of a change in a monitored parameter is accomplished by an inductance non-contacting coil sensor that has a stationary coil which is composed of two parts which are disposed on opposite sides of a spoiler. One part of the stationary coil includes planar metal coil parts (12a, 12b, 14a, 14b) which are located on an insulating board (10). The other part of the stationary coil includes metal coil parts which are located on another insulating board (28). Planar metal coil parts (12a, 12b) which are located on opposite sides of the insulating board (10) are connected via a through hole (16). Similarly, planar metal coil parts (14a, 14b), (30a, 30b), (32a, 32b) are located on opposite sides of their respective insulating boards (10, 28, 28) via respective through holes (18, 34, 36). A spoiler (46) on a shaft (48) is positioned between the two insulating boards. By disposing the spoiler between the two parts of the stationary coil compensation is provided for undesired movements of the spoiler along its rotation axis.

Description: DBSCRIPTION INDUCTANCE COIL SENSOR Technical Field The present invention relates, in general, to sensors which develop signals corresponding to variations in a parameter being monitored. The invention is concerned particularly with a planar inductance coil sensor which has an inductance which varies as the parameter being sensed varies. Background Art Non-contacting sensors are well-known. Such sensors may include one or more stationary inductance coils and a movable member which moves in the field of the stationary inductance coils in accordance with the parameter being 'monitored to change the inductance of the stationary coils. Non-contacting sensors are especially useful because they are not subject to wearing as are those sensors in which the moving and stationary parts are in contact. For example, in a simple potentiometer having a wiper blade which moves along a resistance winding, the constant moving, frictional contact between the wiper blade and the resistance winding will cause wear of one or both parts. Various differently configured non-contacting sensors have been developed in the past. One of these is a planar coil sensor which can be produced by printed circuit techniques. Among the advantages of planar coil sensors are ease of manufacture, relatively low cost, and small size. In one known planar coil sensor, the moving part, sometimes referred to as a "spoiler", is mounted on a shaft for rotary movement into and out of the field of one or more stationary planar coils attached to an insulating board. The position of the spoiler, relative to the position of the stationary coil or coils, is set by the parameter being monitored and determines the change in inductance of the planar coil or coils. Changes in inductance, caused by the spoiler movement, are detected by electronic circuitry which, in turn, provides an output indication corresponding to changes in the parameter being monitored. Many current-day applications of sensors require extremely accurate indications of the parameter being monitored. The particular planar coil sensor described above is subject to errors when the spoiler is displaced in a direction perpendicular to the the plane of the coil. This may be caused by slippage of the spoiler along its mounting shaft or by axial displacement of the shaft itself or by canting of the spoiler relative to its mounting shaft. Instead of altering the field of the planar coil by movement of the - spoiler only within a prescribed plane, the spoiler can undergo different movements, ' which can have an adverse effect on the accuracy of the sensor. Disclosure of the Invention Accordingly, it is an objective of the present invention to provide a new and improved inductance coil sensor . It is another objective of the present invention to provide a new and improved inductance coil sensor in the form of a planar coil. It is a further objective of the present invention to provide a planar coil inductance sensor which is accurate and reliable in operation. These and other objectives are achieved, according to the present invention, by an inductance coil sensor which includes a first insulating board having a planar metal coil attached thereto and a second insulating board disposed parallel to the first insulating board and having a planar metal coil attached thereto. The planar metal coils are connected in a series. The invention also includes a movable planar metal member which is positioned between the two insulating boards and is disposed parallel to the boards. The invention further includes means for moving the movable planar metal member in its plane. Brief Description of the Drawings Referring to the drawings: Figure 1 is an exploded perspective view of a preferred embodiment of an inductance coil sensor constructed in accordance with the present invention; Figure 2 is a sectional view of a portion of the Figure 1 inductance coil sensor; Figure 3 is a schematic diagram showing the connections of the planar coils of the inductance coil sensor of Figures 1 and 2; Figure 4 is a circuit diagram showing how the inductance coil sensor of Figures 1 and 2 can be used; and Figure 5 is a series of waveform diagrams useful in understanding the operation of the Figure 4 circuit. Best Mode of earring Out the Invention Referring to Figures 1, 2 and 3, an inductance coil sensor, constructed in accordance with the present invention, includes a first insulating board 10 having first and second planar metal coils 12a, 12b and 14a, 14b attached thereto. Coils 12a, 12b and 14a, 14b may be formed by conventional printed circuit techniques with each having a generally semi-circular shape. As shown most clearly in Figure 2, coil part 12a is on the top surface of insulating board 10 and coil part 12b is on the bottom surface of insulating board 10. By means of a plated through-hole 16 which extends ' through insulating board 10, coil parts 12a and 12b are connected to form planar metal coil 12a, 12b. This is shown schematically in Figure 3. In a similar manner, coil parts 14a and 14b, on the top and bottom surfaces, respectively, of insulating board 10, are connected by a plated through-hole 18 which extends through insulating board 10 to form planar metal coil 14a, 14b. Terminals 20 and 22 each define one end of cols 12a, 12b and 14a, 14b, respectively, while terminals 24 and 26, shown only in Figure 3, each define the other end of coils 12a, 12b and 14a, 14b respectively. Although coil parts 12a, 12b, 14a and 14b are shown as being generally semi-circular shapes so that adjacent coils form a generally circular shape, these coils, as well as the other coil parts to be described below, can have other shapes. An inductance coil sensor, constructed in accordance with the present invention, also includes a second insulating board 28 having third and fourth planar metal coils 30a, 30b and 32a, 32b attached thereto. Coils 30a, 30b and 32a, 32b may be formed in the same way and arranged in a similar manner • to coils 12a, 12b and 14a, 14b. Coil parts 30a and 30b, on the top and bottom surfaces, respectively, of insulating board 28, are connected by a plated through-hole 34 which extends through insulating board 28 to form planar metal coil 30a, 30b. Coil parts 32a and 32b, on the top and bottom surfaces, respectively, of insulating board 28, are connected by a plated through-hole 36 which extends through insulating board 28 to form planar metal coil 32a, 32b. Terminals 38 and 40 each define one end of coils 30a, 30b and 32a, 32b, respectively, while terminals 42 and 44, shown only in Figure 3, each define the other ends of coils 30a, 30b and 32a, 32b. The inductance coil sensor of the invention further includes means for connecting one of the coils on insulating board 10 in series with one of the coils on insulating board 28 and for connecting the other coil on insulating board 10 with the other coil on insulating board 28. The series connections of the coils is not shown in the exploded perspective view of Figure 1 for the sake of clarity but are represented in the schematic diagram of Figure 3 by the connection of terminals 24 and 38 and the connection of terminals 26 and 40. The series connection of coils 12a 12b and 30a, 30b will be referred to hereinafter as coil 1230 and the series connection of coils 14a, 14b and 32a, 32b will be referred to hereinafter as coil 1432. Positioned between and spaced from insulating boards 10 and 28 is a movable planar metal member 46 which serves as a spoiler as it moves in the space bounded by the two insulating boards. Spoiler 46 is mounted on a shaft 48 which, in turn, is coupled to another rotating component (not shown), the movement of which represents the parameter being monitored. Shaft 48 is disposed perpendicular to the plane of spoiler 46. As the shaft turns in reponse to changes in the parameter being monitored, spoiler 46 moves in its plane between the spaced coils of coil 1230 (coils 12a, 12b and 30a, 30b) and the spaced coils of coil.1432 (14a,. 14b and 32a, 32b). Although shown as a solid par ' t- having a generally semi-circular shape, spoiler 46 can be a wound or coiled article and can have a different shape. As shown in Figure 1, insulating board 28 may be arranged to carry electronic circuit components which make up the circuit which develops indications of changes in the parameter being monitored. This circuit will be considered in greater detail in connection with Figure 4. The various components form an assembly which is held together by a plurality of screws 50, 52, 54, and 56, extending between a pair of insulating blocks 58 an 60, and engaged by a plurality of mating nuts 62, 64, and 66. The nut associated with screw 52 is not shown in Figure 1. Insulating board 10, carrying coils 12a, 12b and 14a, 14b, is spaced from insulating board 28, carrying coils 30a 30b and 32a, 32b, by means of a plurality of spacers 68, 70, and 72 through which screws 50, 54 and 56, respectively, pass. The spacer associated with screw 52 is not shown in Figure 1. In this way, spoiler 46 can be spaced from the insulating boards and the coils carried by the insulating boards, so that there is no physical contact between the spoiler and the coils. The axial position of the spoiler, relative to insulating boards 10 and 28, can be set by a pair of collars 74 and 76 which are fitted over shaft 48 and secured to the shaft by set screws 78 and 80, respectively. Figure 4 shows one circuit which may be used with the inductance coil sensor of Figures 1 and 2 to develop an indication of the position of the spoiler and, therefore, the parameter being monitored. The particular circuit shown in Figure 4 uses multiplex signal processing techniques. The two coils 1230 and 1432 are switched, in timed alternating sequence, to the input of a pulse generator 82 which has a capacitor 84 connected between its input and ground. The switching of coils 1230 and 1432 is accomplised by a switching circuit composed of a pair of transistors 86 and 88 connected in series with coils 1230 and 1432, respectively, a pair of resistors 90 and 92, and an inverter 94. At any particular time, the eoil connected to pulse generator 82 forms a tank circuit with ' capacitor 84. Waveforms (A) and (B) of Figure 5 represent, respectively, the two different resonant frequencies of the tank circuit formed by coil 1230 and capacitor 84 and the tank circuit formed by coil 1432 and capacitor 84. The higher frequency of waveform (B) represents the condition of spoiler 46 being more in the vicinity of coil 1432 than in the vicinity of coil 1230. Waveform (C) represents the output of pulse generator 82. During those periods when coil 1230 is connected to pulse generator 82, the repetition rate of the output of the pulse generator corresponds to the resonant frequency of the tank circuit formed by coil 1230 and capacitor 84. During those periods when coil 1432 is connected to pulse generator 82, the repetiton rate of the output of the pulse generator is higher and correponds to the higher resonant frequency of the tank circuit formed by coil 1432 and capacitor 84. The output of pulse generator 82 is supplied to a counter 96 which measures the amount of time required to count a specific number of pulses. For the example shown in Figure 5, four pulses, two positive-going and two negative-going, are counted, and after the prescribed number of pulses have been counted, a new count is started. With the start of each new count, the output of counter 96 changes level to form pulses having durations corresponding to the time required to count the prescribed number of pulses. This is shown by waveform (D) in Figure 5. The relative time durations of the counter pulses of waveform (D) provide an indication of the position of spoiler 46 relative to coils 1230 and 1432. The output of counter 96 also controls the operation of the switching circuit which switches the input of pulse generator 82 between coils 1230 and 1432. An output indication, representative of the position of the spoiler, is developed by an inverter 98, a pair of resistors 100 and 102, and a pair of capacitors 104 and 106. The signal at a terminal 108 between resistor 100 and capacitor 104 has a " value proportional to: l T l + T 2 where T, and T 2 are identified in Figure 5, while the signal at a terminal 110 between resistor 102 and capacitor 106 has a value proportional to: l + T 2 The difference in the signals at terminals 108 and 110 is proportional to: T l l - T λ 2 T. A change in position of spoiler 46 will change the resonant frequencies of the two tank circuits which, in turn, changes the repetition rates of the output of pulse generator 82. This causes a corresponding change in the values of T. and T_ at the output of counter 96 and thereby changes the difference in the signals at terminals 108 and 110. By locating parts of coils 1230 and 1432 both above and below spoiler 46, a compensation is provided for movements of the spoiler along the axis of mounting shaft 48. As the spoiler undergoes such movements, whereby it approaches or moves away from one part of the coil and produces in that part of the coil a particular effect due to such movements, an opposite effect is produced in the series-connected other part of the coil disposed on the other side of the spoiler. Consequently, great accuracy can be achieved by an inductance coil sensor, constructed in accordance with the present invention, dispite undesired movements of the spoiler which do not represent changes in the parameter being monitored. In addition, by locating part of each coil both above and below the spoiler., less than half of a single coil is required for each part of the coil. Because of the effect of mutual inductance between the two parts of each coil, the total number of turns required for a two-part coil, arranged according to the present invention, is less than the total number of turns required for a one-part coil. Moreover, by locating part of each coil both above and below the spoiler, the present invention can provide a more linear output-signal versus spoiler-position function than would otherwise be provided by a sensor arrangement having a coil part on only one side of the spoiler. With a single coil part, a system using the signal processing technique described above is more sensitive to coil shape design and manufacturing tolerances. The foregoing has set forth an exemplary and preferred embodiment of the present invention. It will be understood, however, that various alternatives will occur to those of ordinary skill in the art without departure from the spirit or scope of the present invention.

Claims: What is Claimed: 1. An inductance coil sensor comprising: a first insulating board having a planar metal coil attached thereto; a second insulating board disposed parallel to said first insulating board and having a planar metal coil attached thereto; means for connecting said planar metal coils in series; a movable planar metal member positioned between and spaced from said first and said second insulating boards and disposed parallel to said first and said second insulating boar s; and means for moving said movable planar metal member in its plane. 2. An inductance coil sensor according to claim 1 wherein one part of each of said planar metal coils is on the top surface of its insulating board and a second part of each of said planar metal coils is on the bottom surface of its insulating board. 3. An inductance coil sensor according to claim 1 wherein said moving means include a shaft upon which said moveable planar metal member is mounted perpendicular to the axis of said shaft and which is adapted for attachment to a rotating part. 4. An inductance coil sensor according to claim 3 wherein said movable planar metal member is a solid part. 5. An inductance coil sensor comprising: a first insulating board having first and second planar metal coils attached thereto; a second insulating board disposed parallel to said first insulating board and having third and fourth planar metal coils attached thereto; means for connecting said first and said third planar metal coils in series and for connecting said second and said fourth planar metal coils in series; a movable planar metal member positioned between and spaced from said first and said second insulating boards and disposed parallel to said first and said second insulating boards; and means for moving said movable planar metal member in its plane. 6. An inductance coil sensor according to claim 5 wherein one part of each of said planar metal coils is on the top surface of its insulating board and a second part of each of said pla-nar metal coils is. on the bottom surface of its insulating board. 7. An inductance coil sensor according to claim 6 wherein each part of said planar coils has a generally semi-circular shape. 8. An inductance coil sensor according to claim 7 wherein said movable planar metal member has a generally semi-circular shape. 9. An inductance coil sensor according to claim 5 wherein said moving means include a shaft having an axis disposed perpendicular to the plane of said movable planar metal member and adapted for attachment to a rotating part. 10. An inductance coil sensor according to claim 9 wherein said movable planar metal member is a solid part. 11. An inductance coil sensor according to claim 8 wherein said parts of said first and said second planar metal coils on said top surface of said first insulating board are adjacent one another to form a generally circular shape, said parts of said first and said second planar metal coils on said bottom surface of said first insulating board are adjacent one another to form a generally circular shape, said parts of said third and said fourth planar metal coils on said top of said second insulating board are adjacent one another to form a generally circular shape, and said parts of said third and said fourth planar metal coils on said bottom surface of said second insulating board are adjacent one another to form a generally circular shape. 12. Sensor apparatus comprising: an assembly of first and second insulating boards and a planar metal member positioned between said insulating boards and spaced therefrom, said first insulating board having a planar metal coil arid said second insulating board having a planar metal coil, said coils connected in series; means for moving said planar metal member into and out of the vicinity of said planar metal coils in accordance with changes in a parameter being monitored to change the inductance of said coils; and circuit means responsive to changes in the inductance of said planar metal coils for developing indications of changes in the parameter being monitored. 13. Sensor appartus according to claim 12 wherein said first and said second insulating boards each have second planar metal coils which are connected in series with each other. 14. Sensor apparatus according to claim 13 wherein one part of each of said planar metal -coils is on the top surface of its insulating board and a second part of each of said planar metal coils is on the bottom surface of its insulating board. 15. Sensor apparatus according to claim 14 wherein each part of said planar coils has a generally semi-circular shape. 16. Sensor apparatus according to claim 15 wherein said movable planar metal member has a generally semi-circular shape. 17. Sensor apparatus according to claim 12 wherein said moving means include a shaft having an axis disposed perpendicular to the plane of said movable planar metal member and adapted for attachment to a rotating part. 18. Sensor apparatus according.to claim 17 wherein said movable planar metal member is a solid part. 19. Sensor apparatus according to claim 14 wherein said parts of said first and said second planar metal coils on said top surface of said first insulating board are adjacent one another to form a generally circular shape, said parts of said first and said second planar metal coils on said bottom surface of said first insulating board are adjacent one another to form a generally circular shape, said parts of said third and said fourth planar metal coils on said top of said second insulating board are adjacent one another to form a generally circular shape, and said parts of said third and said fourth planar metal coils on said bottom surface of said second insulating board are adjacent one another to form a generally circular shape. 20. Sensor apparatus according to claim 12 wherein said circuit means are mounted on one of said insulating boards 21. Sensor apparatus comprising: an assembly of an insulating board having a planar metal coil attached thereto and a planar metal member spaced from said planar metal coil; means for moving said planar metal member relative to said planar metal coil in accordance with changes in a parameter being monitored to change the inductance of said coil; and circuit means mounted on said insulating board and responsive to changes in the inductance of said planar metal coil for developing indications of changes in the parameter being monitored. 22. Sensor apparatus according to claim 21 wherein said planar metal coil is a printed circuit member.

Inventors: FIORI DAVID JR, FIORI, DAVID, JR.
Applicants: FIORI DAVID, FIORI, DAVID, JR.
Application year: 1986
Main classification: H01F21
IPC codes: G01D5, H01F21