Angle Measurement Device Employing Angle Sensor and Electronics Integrally Formed on a Printed Circuit Board

This invention relates generally to angle measurement devices and more particularly to such devices in which the measurement is made with respect to gravity using either a capacitive or resistive sensor.

Several angle measurement devices are known in the prior art, of which U.S. Pat. Nos. 4,503,622, 4,707,927, and 4,547,972 are exemplary. These prior art angle measurement devices typically employ an angle sensor that is physically separated from the electronics employed in the devices. The angle sensors are generally of the resistive type employing a potentiometer having an attached pendulum to reference gravity or of the capacitive type employing a liquid-filled glass vial. The resistive type prior art sensors suffer inaccuracies due to friction in the pivot joint, while the capacitive type sensors employing glass vials are expensive to produce. The physical separation of either type of sensor from its associated electronics is disadvantageous, particularly in the case of capacitive sensors in which the length of leads connecting the electronics to a remotely located sensor or the movement of those leads affects the capacitance of the sensor.

U.S. Pat. No. 4,644,662 is directed to a capacitive type angle sensor that employs a teflon coating on the sensor plates to insulate them from the fluid contained within the sensor and to serve as part of the sealing mechanism. These sensors are also taught to be remotely mounted. The coating on the sensor plates, in conjunction with rings machined into the sensor housing, serves to seal the fluid inside the sensor. However, this sealing arrangement is prone to leakage if the housing screws are not precisely torqued. In addition, the maximum temperature at which these prior art sensors can operate is limited because at higher temperatures the vapor pressure inside the fluid vessel increases to a point beyond which the sealing rings are not effective, thereby permitting the undesirable escape loss of fluid.

It is therefore a principal object of the present invention to provide an improved angle measurement device in which the angle sensor and associated electronics are an integral unit, thereby eliminating the problems associated with prior art angle measurement devices in which those components are physically separated.

It is a further object of the present invention to provide an improved angle measurement device in which the containment of the sensor fluid is accomplished in a way that permits operation at higher temperatures than was previously possible.

It is yet another object of the present invention to provide an improved angle measurement device in which the user may remotely control the electronic gain of the device.

These and other objects are accomplished in accordance with the illustrated preferred embodiment of the present invention by providing a printed circuit board having electronic components mounted on the front surface thereof and having a pair of sensor plates etched into the back surface thereof. Containment of the sensor fluid adjacent the sensor plates is accomplished by soldering a sensor cover to an etched sealing ring on the back of the circuit board. The sensor plates etched into the back of the printed circuit board, in combination with the sensor fluid, act as variable resistors whose resistance changes as a function of their angle of rotation from a reference position. An output signal across these variable resistors is in or out of phase with an applied reference signal. The output signal is demodulated with the same reference signal and then filtered to a DC level that corresponds to the angle of rotation. An output stage serves as a driver and also as a means for permitting the user to remotely control the electronic gain of the angle measurement device.

In accordance with an alternative embodiment of the present invention, a capacitive type sensor may be provided in which a paraylene or solder mask coating covers the sensor plates etched into the back surface of the printed circuit board, but does not extend into the area of the etched sealing ring. This is in contrast to the capacitive type sensor taught in U.S. Pat. No. 4,644,662, mentioned above, in which a teflon coating covers the sensor plates and also acts to seal the resistive fluid within the sensor.

FIG. 1A is a side view pictorial diagram of a resistive type angle sensor formed on the back surface of an electronics printed circuit board, in accordance with the present invention.

FIG. 1B is a cutaway front view pictorial diagram of the angle sensor of FIG. 1A, illustrating the relationship between the sensor plates, sensor fluid, sealing ring, and cap thereof.

FIG. 1D is a front pictorial diagram of the cap that covers the angle sensor of FIGS. 1A-C.

FIG. 2 is a detailed schematic diagram of electronic circuitry that is mounted on the front surface of the printed circuit board of FIGS. 1A-D to form, in combination with the angle sensor of FIGS. 1A-D, an angle measurement device in accordance with the present invention.

Referring now to FIGS. 1A-D, there is shown a conventional copper clad printed circuit board 10 having electronic circuit components 70 mounted on a front surface thereof and having an encased angle sensor 80 formed on a back surface thereof. Together, electronic circuit components 70 and angle sensor 80 comprise the angle measurement device of the present invention. Angle sensor 80 comprises a pair of sensor plates 20, 30 that are etched from a copper clad surface layer of printed circuit board 10. A copper cap 40 is soldered to a sealing ring 60 that is also etched from the copper clad surface layer of printed circuit board 10. The copper cap 40 serves to enclose the sensor plates 20, 30 in the presence of a conventional resistive sensor fluid 50 that occupies approximately one-half of the volume enclosed by copper cap 40. In accordance with an alternative embodiment of the present invention, a capacitive type sensor may be provided in which a paraylene or solder mask coating 12, illustrated in FIG. 1A, covers the sensor plates 20, 30 etched into the back surface of printed circuit board 10. Coating 12 does not extend into the area of etched sealing ring 60.

Referring now to FIG. 2, there is shown a detailed schematic diagram of the circuitry comprising circuit components 70, illustrated in FIG. 1A as being mounted on the front surface of printed circuit board 10. The circuitry of FIG. 2 comprises dual function and dual gain circuitry that is powered by a positive and negative DC supply voltage in the range of 8-24 volts applied at terminals 1 and 2, referenced to a ground terminal 3. A multivibrator 4 generates in-phase and out-of-phase signals 5, 6 that are impressed on the right and left sensor plates 30, 20, respectively, of FIGS. 1B and 1C. As the angle sensor 80 of FIGS. 1A-D is rotated about its axis, more of the right or left sensor plates 30, 20 will be covered by the resistive sensor fluid 50 and, consequently, more or less of the signals 5, 6 will be coupled to a driver amplifier 9. A capacitor 100 and resistor 11 serve to reference the output of driver amplifier 9 to ground. A conventional analog switch 26 is employed to demodulate the signal received from driver amplifier 9, using the out-of-phase signal 6. The resultant demodulated signal is applied to a driver amplifier 12, the output of which is filtered by means of a resistor 13 and capacitor 14 to a DC level corresponding to the angular rotation of angle sensor 80, with the polarity of the DC level corresponding to the phase rotation of angle sensor 80. Resistors 15, 16, 17, 18 determine the gain of an output stage amplifier 19. A switch 200 is provided to short resistor 16, thereby enabling the user to switch between two gain settings by means of a jumper 21.

In the event it is desired to configure the electronic circuitry of FIG. 2 for the ratiometric mode, jumpers 22, 23, 24 will be connected, and a positive supply voltage within the range of 5-18 volts will be applied at terminals 1, 2. Jumper 24 will serve to apply one-half the supply voltage on the ground terminal. In this rationmetric mode, the circuitry of FIG. 2 will perform as described above, except that the output will be referenced to one-half the supply voltage. If the supply voltage is 10 volts and the angular rotation of angle sensor 80 is zero degrees or null, the output voltage at terminal 25, with reference to terminal 2, will be 5 volts. As the angle sensor 80 is rotated clockwise, the output voltage at terminal 25 will increase toward 10 volts, and as the angle sensor 80 is rotated counter clockwise, the output voltage at terminal 25 will decrease from 5 volts toward zero.