Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-06-04
2004-03-23
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C092S00500L
Reexamination Certificate
active
06710327
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to position sensing of hydraulic and pneumatic actuators. More particularly, it relates to sensing using laser light sources and detectors and determining the position of the actuator using time-of-flight algorithms.
BACKGROUND OF THE INVENTION
Position sensing for hydraulic or pneumatic actuators typically uses an external position sensor, such as a rotary rheostat or potentiometer. Alternatively, linear rheostats or variable differential transformers are employed. These systems suffer from poor accuracy, extensive wear, and fragility in many applications, especially demanding applications such as their use on work and agricultural vehicles.
These sensors are quite susceptible to damage, and suffer from being damaged during vehicle operation, or from the extremes in temperature that work and agricultural vehicles face.
In an effort to solve these problems, new methods of measuring the position of a hydraulic or pneumatic actuator have been devised that use microwaves. These waves are transmitted from one end of the cylinder, reflect off the piston, and return to a detector. By measuring the time-of-flight of these waves, the location of the piston can be determined. Such an example is shown in U.S. Pat. No. 6,005,395, which is incorporated herein by reference for all that it teaches.
The microwave transmitter suffers from high cost and difficulties in determining which of the many reflections in the cylinder is the proper one to measure.
In an alternative system, the pulse generating and timing circuits of U.S. Pat. No. 6,005,395 are used, but are coupled to a laser light source and respond to a reflection of that beam against a laser light detector, such as that shown in co-pending U.S. patent application Ser. No. 09/750,866.
This arrangement also has drawbacks. When the piston moves toward or away from the source and detector, the reflected light follows multiple paths that, like the microwave transmitter and receiver pair, make the reflected pulses difficult to interpret. It is difficult to extract a good pulse indicative the precise time-of-flight of the laser beam.
An improvement on this system is provided in our co-pending application entitled “MULTI-FIBER CYLINDER POSITION SENSOR USING TIME-OF-FLIGHT TECHNIQUE”, docket number 13936 and filed contemporaneously herewith. In that application, a single optical fiber transmits laser-light pulses from outside a hydraulic or pneumatic cylinder to inside the cylinder. The fiber is preferably located along a central longitudinal axis of the cylinder. The light pulses from the transmitting fiber travel down the cylinder substantially parallel to the longitudinal axis of the cylinder and reflect off the face of the piston in the cylinder. The light is reflected straight back toward the transmitting fiber. The path it follows in returning to the transmitting fiber at the end of the cylinder is substantially the same path as the path it traveled when going from the fiber to the piston. In short, the laser beam is preferably normal to the piston where it is reflected in order to provide these parallel in and out paths. When the laser light pulses return to the region of the transmitting fiber, they fall on the free ends of several optical fibers disposed around the central transmitting fiber. All of these fibers receive the light pulses at substantially the same time and conduct the light pulse from inside the cylinder to outside the cylinder. The receiving fibers are closely spaced in a circular arrangement equidistant from the central fiber. Since the light pulse from the central fiber follows the same path back after reflecting from the piston, each of the fibers receives approximately the same amount of light energy, and receives it at almost exactly the same time.
The distal ends of the receiving fibers are coupled together such that each portion of the reflected light pulse that each individual fiber of the receiving fiber carries are merged to form a much stronger light pulse. The lengths of the receiving optical fibers are chosen such that the portions of the reflected light pulse that each one carries is merged into a single pulse at exactly the same time. This sharply increases the magnitude of the resulting pulse and provides an extremely fast and sharp rise time. In this manner, a reflected light pulse can be “reassembled” with a very sharp leading edge that permits precise time-of-flight measurements.
The system described in the foregoing patent application, however, discloses a separate laser diode and separate photodiode for use with a single cylinder. In addition, there is complex and expensive circuitry to expand the light pulse and compare the phases of the transmit and receive pulses to determine the time-of-flight in a cylinder, and thereby the position of the piston within the cylinder.
Duplicating this structure in a vehicle that has several hydraulic or pneumatic cylinders would be prohibitively expensive. Multiplying the arrangement of the 13936 application would require as many laser diodes, photodiodes, amplifier circuits, pulse expansion circuits and phase comparators as there are individual cylinders. What is needed, therefore, is a system that can measure the position of several hydraulic cylinders, yet does not require duplicate sets of circuitry for each of those cylinders. It is an object of this invention to provide such a system.
SUMMARY OF THE INVENTION
In accordance with a first embodiment of the invention, a multiple cylinder position sensing system is provided that includes a first cylinder including a first source light guide having a first end and a distal second end and extending from inside the cylinder to outside the cylinder and adapted to transmit at least a first beam of laser light at a first frequency from outside the cylinder to inside the cylinder, and at least one first reflected light guide having a first end and a distal second end and extending from inside the cylinder to outside the cylinder and configured to receive light from the first beam of laser light that is reflected off the inside of the first cylinder, and a second cylinder including a second source light guide having a first end and a distal second end and extending from inside the cylinder to outside the cylinder and adapted to transmit at least a second beam of laser light at a first frequency from outside the cylinder to inside the cylinder, and at least one second reflected light guide having a first end and a second end and extending from inside the cylinder to outside the cylinder and configured to receive light from the second beam of laser light that is reflected off the inside of the second cylinder.
The system may include a laser light source that is optically coupled to the distal ends of both the first and second source light guides, and configured to generate a source beam of laser light, wherein the source beam is divided into the first and second beams of laser light. The system may include a first photodiode configured to receive and electrically respond to light from the first beam of laser light that is reflected off the inside of the first cylinder from the first reflected light guide. The system may also include a laser light source driver circuit coupled to the laser light source and configured to energize the laser light source upon receipt of a trigger pulse, and a timing circuit coupled to the laser light source driver configured to generate the trigger pulse and apply the trigger pulse to the laser light source driver circuit. The laser light source may be a laser diode. The system may include first and second photodiode amplifiers that are coupled to the first and second photodiodes, respectively.
Each of the first and second photodiode amplifiers may be configured to generate an output signal.
The system may also include a pulse expansion circuit, to which the first and second photodiode output signals are coupled.
The second ends of the plurality of second light guides may be optically coupled to a single light detector. The light dete
Arshad Mohammad Javaid
Berger Alan D.
Chan Danley C.
Maierhafer Daniel L.
Case LLC
Henkel Rebecca
Maurer Brant T.
Pyo Kevin
LandOfFree
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