Abstract:
A non-contact linear position center has juxtaposed transmit and receive sections with a coupler or slider section interposed therebetween carrying a symmetrical attenuating conductive pattern. The inductive coupling of coils on the transmitter and receive sections is attenuated in accordance with the linear position of the pattern on the coupler. A unique sinusoidal signal is generated whose phase is indicative of the linear position of the coupler.

Description:
RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent application Ser. No. 09/390,885, filed Sep. 7, 1999, entitled ANGULAR POSITION SENSOR WITH INDUCTIVE ATTENUATING COUPLER and now U.S. Pat. No. 6,304,076. 
    
    
     INTRODUCTION 
     The present invention is directed to a non-contact linear position sensor for motion control applications. 
     BACKGROUND 
     In order to meet the current stringent reliability and meantime before failure (MTBF) requirements demanded by the automotive, industrial and aerospace industries, position sensors must be based on a non-contact design approach. For automotive use, the design must be suited for low cost, high volume, and high reliability. The above parent application discloses and claims an angular position sensor which is useful, for example, in the automotive field for determining the rotation of a steering column. This same type of non-contacting position sensor can also be adapted to measure the torque in a steering column as disclosed in a co-pending application, Ser. No. 09/527,088 (now U.S. Pat. No. 6,304,076), filed Mar. 16, 2000, entitled, NON-CONTACTING TORQUE SENSOR and assigned to the present Assignee. However, there is still a need for a linear position sensor, for example, one that may be used with a voice-coil actuator in order to provide built-in feedback control for motion control applications. 
     OBJECT AND SUMMARY OF INVENTION 
     It is therefore a general object of the present invention to provide a non-contact linear position sensor for motion control applications. 
     In accordance with the above object there is provided a position sensor for sensing rectilinear movement of an object along an axis comprising a pair of spaced substantially rectilinear radio transmit and receive sections juxtaposed on the axis facing each other with a coupler section between them, the coupler being movable along the axis and connected to the object. The receive section carries a predetermined number of independent inductive coils segmentally arranged in a rectilinear pattern along the receive section. The transmit section carries coil means in a rectilinear pattern similar to the receive section and is driven by a signal source at a predetermined radio frequency for inductive coupling to the coils of the receive section. The coupler section carries at least one symmetrical conductive pattern for attenuating the inductive coupling, the pattern having linear positions of maximum and minimum attenuation with respect to any one of a plurality of inductive coils carried by the receive section, intermediate positions of the pattern between the maximum and minimum providing substantially proportionate attenuations. Means connected to the coils carried by the receive section demodulate and sum induced transmitted signals from the signal source for each linear position of the coupler, the summation producing a substantially sinusoidal waveform whose phase shift varies in proportion to the linear movement coupler section. Means are provided for sensing the phase shift. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a plan view of both the transmit and receive portions of an angular position sensor as disclosed in the above parent application. 
     FIG. 2 is a plan view of a coupler disk as used in the angular position sensor of the above parent application in conjunction with the transmit and receive portions of FIG.  1 . 
     FIG. 3A is a simplified plan view of a transmitter section of the present invention. 
     FIG. 3B is a simplified plan view of a slider or coupler section of the present invention. 
     FIG. 3C is a simplified plan view of receiver section of the present invention. 
     FIG. 4 is a simplified circuit schematic illustrating the present invention. 
     FIG. 5 is a detailed schematic of a portion of FIG.  4 . 
     FIGS. 6A,  6 B,  6 C and  6 D are wave forms illustrating the operation of the invention. 
     FIG. 7 is a cross-sectional view of a voice coil actuator incorporating the position sensor of the present invention. 
     FIG. 8 is a end view taken along the line  8 / 8  of FIG.  7 . 
     FIG. 9A is another illustration of FIG.  3 B. 
     FIG. 9B is the characteristic curve of the electrical output provided by FIG.  9 A. 
     FIG. 9C is an alternate embodiment of FIG.  9 A. 
     FIG. 9D is a characteristic output of the alternate embodiment shown in FIG.  9 C. 
     FIG. 9E is an alternate embodiment of FIG.  9 A. 
     FIG. 9F is a characteristic output of the alternate embodiment shown in FIG.  9 E. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1 and 2 these illustrate the angular position sensor of the parent application where the disk  10  illustrates both the transmit and receive sections or disks which contains six identical loop antenna coils designated for the transmit portion T 1 -T 6  and for the receive section R 1 -R 2 . A coupler disk  11  as illustrated in FIG. 2 is sandwiched between the transmit and receive disks and rotation of the crescent-shaped conductive portion of the coupler disk causes a phase shift in the signals from the receive coils which is proportional to rotary or angular displacement. As illustrated in FIG. 1, the coils are spaced 60° apart. 
     The present invention utilizes the above principle to measure linear displacement. Thus, FIG. 3A is a transmitter section  13  having six inductive coils T 1 -T 6  arranged in a rectilinear pattern with a total distance L a  with a width of L b . A similar rectilinear receive section  14 , FIG. 3C, has similar receive coils R 1 -R 6  and includes a specialized electronics integrated circuit unit  15  to provide output voltages designated R out  for each receive coil. Then juxtaposed between the transmitter and receiver sections  13  and  14 , is a slider on coupler section  12  having substantially symmetrical diamond shaped coupler patterns  51  and  52  (see FIG. 3B) which are conductive with a nominal length of each pattern being designated L c . Thus, movement of the coupler section in the direction  53  attenuates the inductive coupling between transmitter and receiver sections  13  and  14  to produce an output signal (to be discussed below) whose phase shift varies with the amount of attenuation, which is proportionate to linear displacement. 
     FIG. 9A shows the coupler section  12  and the electrical signal output related to the distance L c  is illustrated as a straight line in FIG.  9 B. To generate an effective signal, generally the total length of the slider section  12  is as illustrated equal to L c  plus L a . Thus the patterns  51  and  52  for a longer displacement must be repeated several times and from a practical standpoint, there must be one additional diamond-shaped section  51 ,  52 , etc. more than is necessary for the total distance to be measured. And also, in general, L c  is equal or less than L a . Thus, for a long multi-sectioned symmetrical pattern on slider section  12 , a cycle counter is required to identify the effective revolutions or repetitions. This insures that the transmitter and receiver are exposed to the total length of the pattern on the slider section  12  at all times. 
     FIG. 4 illustrates the transmitter and receiver sections  13  and  14  with the slider or coupler section  12  interposed, which will move in a linear manner as indicated by the arow  53 , in association with the electrical signal processing circuit. A signal source  17  supplies a signal, F c  to the coils of the transmit section  13  which are inductively coupled to receive section  14  and attenuated by the slider section  12 . Signal  17  is also connected to a digital mixer and waveform generator  16  which also has as an input  31 , the six receive coils, on output line  32 , a set (S) signal is suppled to an RS flipflop. 
     Since the coupler or slider section will interrupt and attenuate the signal amplitudes based on the coupler pattern with respect to the position of each receiver coil, six different amplitude signals are simultaneously generated by an amplifier A 1  and then input through a lowpass filter and limiting amplifier A 2 . The output signal of amplifier A 2  is illustrated in FIGS. 6A,  6 B,  6 C and  6 D which represents four different linear positions of the coupler or slider. Their phase shift is proportional to the linear position of the coupler or slider. 
     Referring back to FIG. 4 comparator to A 3  then converts these waveforms to a square wave at output  36  which drives the R input of the RS flipflop. This produces a pulse width modulator (PWM) output where the width of the pulse is exactly proportional to the amount of movement of the slider. Filter A 4  provides an alternative analog output. 
     FIG. 5 illustrates the digital mixer and waveform generator  16  and how it is related to the transmitter and receive coils  13  and  14 , including being driven by six local oscillator signals L 01 -L 06  which are shifted in phase from one another by 60°, i.e., by the number of receive coils cited in 360°. The foregoing is more totally explained in conjunction with the parent application. 
     An actual practical example of the position sensor of the present invention for measuring the displacement of a voice coil actuator is illustrated in FIGS. 7 and 8, where FIG. 7 is a voice coil actuator  61  incorporating the position sensor and FIG. 8 shows the position sensor with its transmit section  13 , slider or coupler section  12  and receiver section  14  incorporated in the actuator. The transmitter and receiver are, of course, affixed to the frame  62  of the voice coil actuator with coupler or slider  12  as best illustrated in FIG. 7 being connected only to coil holder  63 , which moves in the direction as indicated by the arrow  64 . It would be coupled to an actuated device such as the valve lifter of a diesel engine or some control device to control vehicle height. Movable coil holder  63  of actuator  61  includes a tubular coil  66  wrapped around it which interacts with the cylindrical ferromagnetic permanent magnet  67  through the air gap  68  in a manner well known in the art. The fixed outer frame  62  of the voice coil actuator is composed of soft iron for a flux return and is, of course, cylindrical in shape. The voice coil actuator may be used in conjunction with built in feedback control. 
     Referring now to FIGS. 9 in their various forms, as was discussed the diamond shape of the symmetrical pattern on the slider section  12  illustrated in FIG. 9A results in the linear pattern of FIG.  9 B. If a second order characteristic is desired at either one end or the other end of movement of the slider  12 , as illustrated in either FIGS. 9D and 9F, then the patterns of FIGS. 9C, and  9 E, respectively, may be provided where in FIG. 9C the rate of change toward the maximum of the pattern is greater and in  9 E the rate of change at the beginning of the pattern is greater. 
     Thus a linear position sensor has been provided.