FLIP-FLOP

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3,501,966

PHOTODYNAMIC PICKOFF MEANS HAVING A PULSE DURATION MODULATED OUTPUT Sol Shapiro, Oakland, and Constant J. De Cotiis, Cranford, N.J., assignors to Singer-General Precision, Inc., 5 a corporation of Delaware

Filed Dec. 4, 1967, Ser. No. 687,860
Int. CI. GOlc 19/28
U.S. CI. 74—5.6 11 Claims

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ABSTRACT OF THE DISCLOSURE

The pickoff system includes a light source and lens arrangement mounted on the housing for directing a parallel incident light beam toward one of the spin axis 15 poles of the rotor member along the stator reference axis. A coplanar mirror is mounted on the rotor member at the aforementioned spin axis pole to reflect the parallel incident light beam and form a reflected light beam which lies at an acute angle with respect to the rotor 20 spin axis, so that the spinning rotor member causes the reflected light beam to rotate about the spin axis and trace a circular path. The center of this circular path will be free to move along two, mutually-perpendicular lines of movement which represent the agular deviations ^ between the rotor spin axis and the stator reference axis in the first and second planes. A photodetector having four independently operable, substantially coplanar portions which are defined by a pair of mutually-perpendicular dividing lines is mounted on the interior of the housing for actuation by the rotating reflected light beam. The photodetector is so oriented that the two dividing lines are coincident with the two, mutually-perpendicular lines of movement of the center of the circular path, so that the center of the circular path coincides with the point of intersection of the dividing lines of the photodetector and each of the four portions of the photodetector produce a series of output pulses having a pulse repetition rate corresponding to the rotor spin speed 40 with the time durations or "widths" of all of the pulses being equal. When the rotor spin axis deviates from the stator reference axis, the center of the path traced by the reflected light beam on the photodetector will be shifted from the point of intersection of the dividing lines ^ and the pulse widths of the four series of pulses will become unequal, so that the relative magnitudes of the pulse widths of the four series of pulses will completely define the angular position of the rotor spin axis with respect to the stator reference axis. Ka

BACKGROUND OF THE INVENTION
Field of the Invention

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This invention relates generally to spatial orientation responsive devices and the like and more particularly to photodynamic pickoff means therefor having the capability of supplying two-axis positoinal information in the form of output signals of the pulse duration modu- gQ lated type.

Description of the prior art

Spatial orientation responsive devices, such as directional gyroscopes, rate gyroscopes, angular accelerom- gg eters, and the like, are often employed in aircraft and guided missile applications to provide output signals which represent some aspect of the attitude or motion of the vehicle in which the devices are mounted. A common form of spatial orientation responsive device utilizes a stator member which is fixed in position with respect to the vehicle in which the device is mounted and

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a spinning rotor member which has one or more degrees of freedom of movement. The spinning rotor member acts as a reference against which positional and motional deviations of the stator and vehicle may be measured. The angular deviations between the rotor spin axis and a stator reference axis in one or more planes representing the degrees of freedom of the device may then be utilized to provide directional, rate or acceleration signals depending upon the application and type of equipment involved. In order to obtain these signals, however, it is necessary to employ a pickoff system which functions to convert the positional difference between the rotor and stator members of the device into an output signal which represents the desired quantity being measured.

A pickoff system which is suitable for use with present day spatial oriention responsive devices should preferably satisfy a number of requirements. For example, it is desirable that the pickoff system produce output signals of the pulse duration modulated type, wherein the informational content of the signal is expressed as the time duration or "width" of the pulses making up the signal rather than the amplitude of the pulses. Signals of this type, which are often refered to as "pulse width modulated signals" may be amplified by a variety of nonlinear, bistable or switch type amplifiers. Pulse duration modulated signals have a dual nature in that they may be used directly as digital signals with the many forms of digital computers and control equipment in use at the present time without the need for undesirable analogto-digital conversion systems or may be easily converted to analog signals by relatively simple circuit means, such as R-C low pass filters, for example, which function to derive the average value of the series of pulses forming the pulse duration modulated signal. A suitable pickoff system should also be capable of performing its required sensing function without extering any restraining force or "drag" on the rotor member of the spatial orientation responsive device with which the pickoff system is associated. Should such a restraining force be exerted, it is apparent that the operational accuracy of the device could be seriously compromised. This requirement becomes extremely important when the kickof system is employed with gyroscopes of the free-rotor, gas bearing type wherein the rotor member is supported with respect to the stator member by a thin film of gas to provide virtually frictionless operation. It may also be noted that a suitable pickoff system for spatial orientation responsive devices employed in aircraft and guided missile applications must meet the ever present requirements of high accuracy, mechanical ruggedness and reliability of operation which are dictated by the field of application.

A photodynamic pickoff system meeting the aforementioned requirements is disclosed in a copending U.S. patent application of Constant J. De Cotiis for "Photodynamic Pickoff Means Having A Pulse Duration Modulated Output," Ser. No. 687,552 filed on the same date as the present application and assigned to the same assignee as the present application. The pickoff system disclosed in the aforementioned copending patent application employs a light source mounted on either the stator or motor member of the spatial orientation device with which the pickoff is used and a light transmitting aperture formed in the rotor member to produce a light beam which rotates about the spin axis of the rotor as the rotor member spins. A four-section photodetector is employed to translate the closed path traced by the rotating light beam into four series of output pulses having relative pulse widths which are dependent upon the angular deviation between the rotor spin axis and the stator reference axis. The relative magnitudes of the pulse widths forming the four series of pulses serve to completely define the 3

angular position of the rotor spin axis with respect to the stator reference axis in two, mutually-perpendicular planes representing the two degrees of freedom of the gyroscope rotor. When a photodynamic pickoff system of this type is used with a two-axis, free-rotor gyroscope of r the type disclosed in U.S. Patent No. 3,416,378 by John 0 L. Evan, et al., for "Free-Rotor Gyro," the light source for the pickoff must be disposed in the spherical stator member of the gyroscope. Since the rotor member of the gyroscope is mounted for rotation about the center 1Q of the spherical stator member by hydrostatic gas bearing means, the interior of the stator member must contain the necessary passages for admitting the pressurized gas which creates the gas bearing, with the result that it is difficult to physically place the light source within the ig stator member. Additionally, since the light source is disposed within the pressurized interior of the gyroscope, it is necessary to use pressure seals to make the necessary electrical connections to the light source. When the aforementioned photodynamic pickoff system is utilized with 20 a gas bearing gyroscope of the type disclosed in U.S. Patent No. 3,187,588 granted to Bernard Parker on June 8, 1965, the light source for the pickoff must be disposed within a spherical rotor member of the gyroscope, since a gas bearing gyroscope of this type employs 25 a spherical rotor which is concentrically disposed within a spherical cavity formed in the stator member. It is accordingly necessary to provide a battery or other means within the spinning rotor member to energize the light source, thereby adding to the weight of the spinning rotor 30 member. Finally, in the pickoff system disclosed in the aforementioned copending patent application of Constant J. De Cottis, the rotating light beam produced by the aperture formed in the rotor member is in the nature of a diffused cone of light rather than a defined or parallel 35 light beam, with the result that the light available from the light source is not used with maximum efficiency and the output signals produced by the photodetector are not at the highest possible levels.

SUMMARY OF THE INVENTION

It is an object of this invention to provide pickoff means of the photodynamic type for spatial orientation responsive devices and the like, wherein the light source and photoelectric transducer means of the pickoff may 45 be compactly packaged and mounted exteriorly of the housing of the spatial orientation responsive device, thereby facilitating the mounting of the piqkoff on the device and eliminating the need for pressure seals for electric wiring associated with the pickoff. 50

It is a further object of this invention to provide pickoff means of the photodynamic type for spatial orientation responsive devices and the like, wherein a defined, parallel light beam is employed to efficiently utilize the available energy from the light source of the pickoff and 55 produce a high intensity light spot on the photoelectric transducer means of the pickoff, thereby increasing the level of the output signals from the pickoff.

It is a still further object of this invention to provide pickoff means of the photodynamic type for spatial 60 orientation responsive devices and the like, wherein a small mirror or other light reflecting device is the only component part of the pickoff which must be mounted on the spinning rotor member of the device, thereby facilitating the use of the pickoff with a wide variety of dif- 65 ferent types of gyroscopes and other spatial orientation responsive devices having gas bearing means.

It is another object of this invention to provide pickoff means of the photodynamic type for spatial orientation responsive devices and the like, wherein means are pro- 70 ■vided for decreasing the size of the light spot formed by the rotating light beam of the pickoff on the photoelectric transducer means thereof, to thereby sharply define the limits of the effective operating range of the pickoff, 75

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Briefly, the photodynamic pickoff means of the invention, as applied to a spatial orientation responsive device of the type wherein relative angular movement is permitted between the rotor spin axis and the stator reference axis in at least one plane in which both axes lie, comprises means mounted on the stator member of the device for producing a parallel incident light beam directed toward one of the spin axis poles of the rotor member. Light beam reflecting means are mounted on the rotor member at the said spin axis pole for reflecting the incident light beam to form a reflected light beam which lies at an angle with respect to the rotor spin axis, so that the spinning of the rotor member causes the reflected light beam to rotate about the spin axis and thereby trace a closed path. The line of movement of the center of the closed path will then represent the angular deviations between the rotor spin axis and the stator reference axis in the aforementioned plane. Photoelectric transducer means having at least two independently operable portions are mounted on the stator member for actuation by the rotating reflected light beam. The two portions of the transducer means are disposed on opposite sides of a dividing line which is arranged to be perpendicular to the line of movement of the center of the closed path traced by the reflected light beam. The dividing line is also arranged to bisect the closed path when the rotor spin axis coincides with the stator reference axis, so that each of the transducer portions produces a series of output pulses having a repetition rate corresponding to the rotor spin speed. Since the pulse width of each series of output pulses depends upon the length of the path traced by the reflected light beam on the transducer portion associated with that series, any deviation of the rotor spin axis from the stator reference axis will cause the pulse widths of the two series of pulses to become unequal and the magnitude and sense of the pulse width differential will respectively represent the magnitude and direction of the aforementioned deviation between the spin axis and the reference axis.

When the pickoff means of the invention is employed with spatial orientation responsive devices wherein relative angular movement between the rotor spin axis and the stator reference axis is permited in first and second mutually-perpendicular planes in which the reference axis lies, the photoelectric transducer means has four independently operable portions which are defined by the intersection of a pair of mutually-perpendicular dividing lines. Since the center of the closed path traced by the reflected light beam is now free to move along two, mutually-perpendicular lines of movement, the transducer is so mounted on the stator member that the dividing lines of the transducer quadrisect the closed path traced by the light beam when the rotor spin axis and the stator reference axis are in alignment. By virtue of this arrangement, the four series of output pulses from the transducer means will have pulses of the same width when the rotor spin axis and the stator reference axis are aligned and will have unequal widths when an angular deviation occurs between the two axes. The relative magnitudes of the pulse widths of the four series of output pulses will then completely define angular deviations between the rotor spin axis and the stator reference axis in both of the first and second planes. Suitable circuit means are also provided for combining the four series of output pulses from the photoelectric transducer means to derive two pulse duration modulated output signals which represent the magnitude and direction of the angular displacement of the rotor spin axis from the stator reference axis in the two planes. In order to facilitate the physical placement of the photoelectric transducer means on the stator member with respect to the incident light beam producing means, the invention also contemplates the use of light beam splitting means which are mounted on the stator member at a point along the reference axis thereof for transmitting the incident light beam along