Data processing: generic control systems or specific application – Specific application – apparatus or process – Mechanical control system
Reexamination Certificate
1999-09-14
2001-04-10
Gordon, Paul P. (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Mechanical control system
C700S054000
Reexamination Certificate
active
06216059
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to a method and apparatus for controlling the motion or vibration of mechanical systems. More specifically, the invention describes a method for employing a single transducer for both the detection of motion and/or vibration and the application of motive force for the purpose of influencing and controlling the motion and/or vibration.
Definition of Terms and Discussion of Suitable Transducers for use in the Invention
The terms “subject” and “subject mass” shall refer to the thing being controlled. As used herein these terms include but are not limited to a elastic mechanical system capable of one or more modes of vibration.
The term “control system” shall refer to the entire means coupled to the subject and employed to influence the state of the subject according to a reference or guiding signal or signals.
The term “controller” shall refer to the circuit means connected to the transducer. The controller comprises the sensing circuitry, the signal processing circuitry and the actuating circuitry that exists for the purpose of causing the subject to behave in accordance with a reference input.
The term “reference” shall refer to information about the desired state of the subject that may be provided to the control system. The control system's goal is to make the state of the subject conform to the reference. The reference information may be time domain data, frequency domain data, wavelet data, or any form appropriate to the particular calculations and algorithms of the control system. All control systems have a reference input, though in some cases this input may be implicit rather than explicit. For example, an input of zero may exist implicitly in a system designed only to dampen vibration.
The term “correction signal” shall refer to the output of the processor in the control system. It is the signal that the controller calculates must be applied to the transducer actuating time-channel in order to compel the subject's state to conform to the reference. In standard control system terminology, the term “error signal” roughly corresponds to the present term “correction signal”. In one embodiment of the invention described herein, there is an error signal that is distinct from the correction signal.
The term “transducer” shall refer to the physical means through which the control system interacts with the subject. A “sensing transducer” inputs information about the subject to the control system. A “forcing transducer”, also known herein as an “actuator”, outputs a force under direction of the control system to effect changes in the state of the subject. A transducer may be capable of functioning as only a sensor, or as only a source of force, or as both. A transducer employed in the control system of this invention serves both functions, i.e., sensing and actuating.
The term “damping” shall refer to active damping as against passive damping. Passive damping is an example of a shorted generator and as such the power of the applied damping cannot be more than that available from the subject mass itself. In contrast to this, one of the present invention's capabilities is active damping, defined herein as the removal of energy from a vibrating mechanical system by the deliberate application of amplified force in opposition to the vibration.
Transducers capable of reciprocal, complimentary sensing and forcing functions and thus suitable for use with the present invention include but are not limited to the following:
Electromagnetic transducers that generate a signal in response to a changing magnetic field and emit magnetic force as a result of an applied current; and
Piezoelectric transducers that generate a voltage signal in response to a change in mechanical stress and change shape or exert a force in response to an applied voltage.
One contrasting example of a transducer that is not suitable for use with the invention is of the photo-modulation type. In this transducer, the motion of the subject modulates the transmission of light to a photo receptor, yielding a signal representative of that motion. This transducer is capable of sensing but not of actuating.
Discussion of Selected Prior Art and Objects of the Invention
Time-Channel Isolation Between Sensor and Actuator:
One goal of the invention is to solve the problem of unwanted coupling between sensor and actuator. For example, a prior art musical string sustaining system displayed in U.S. Pat. No. 5,523,526 (“'526 patent”), presents a variety of techniques for overcoming the problem of unwanted coupling between actuators and sensors in a control system, but none is as simple or as successful in practice as the present invention. In a control system, loop gain is often limited primarily by the degree of the direct response of the sensor to the actuator. Known techniques to reduce this include shielding between sensor and actuator and subtraction of unwanted coupling. The goal of all such techniques is that the sensor should sense the state of the subject but not of the actuator. In the present invention, isolation is accomplished by time-separation. Sensing is performed at a time after the application of force has been stopped, when field effects that create unwanted coupling have subsided. Thus the sensor reads the new state of the subject resulting from the previous application of force, but the sensor does not respond to the actuating force itself.
The present invention provides any arbitrary degree of time-channel isolation. As it is possible to wait almost forever between forcing and sensing events, the isolation can be almost infinite. In practice, there is a trade-off between isolation and sampling frequency. The parameters of this compromise are dependent upon the particular transducer technology and material composition. Combinations of technologies and materials that support an extraordinary degree of isolation at relatively high sampling rates do exist; an electromagnetic transducer employing magnetic materials having low losses at high frequencies is but one example.
Control of Multiple Subjects in Parallel:
It is a further goal of the invention that a plurality of subjects and associated control systems may operate in close proximity to each other without significant compromise. Each subject, individually associated with one instance of the control system, may be controlled by a unique control loop function or by the same control loop function without cross interference between the control systems. This is facilitated by the definite and discrete timing structure of the invention. As a result, a plurality of parallel control systems may be synchronized in time. All sensing events and actuating event time channels may be coincident. Within such an array of control systems, any one control system's sensing function may be as isolated in time from an adjacent control system's actuating event as it is from its own actuating event.
Scaling of Mass and Frequency:
A further goal of the invention is that it should be applicable to subjects having small mass as well as those having large mass. The invention exhibits a natural complimentary scaling of mass and frequency: A decrease in transducer and subject geometry favors an increase in operating frequency and vice versa. Everything may be scaled together in a complimentary fashion, permitting a wide latitude of application.
Compact Design:
Another goal of the invention is that the transducer means be of compact design. The single transducer of the invention provides an advantage in this respect over prior, dual transducer systems.
Sensing of Velocity and of Position:
A further object of the invention is to enable the sensing of both velocity and position of the subject mass. In cases where an electromagnetic transducer is employed it is possible to exploit the settling behavior of the actuation transient to detect the proximity of the subject mass. This facilitates control of both position and motion. A detailed explanation of this follows further below.
Variable Control Rate:
Cabrera Zoila
Gordon Paul P.
Jackson Harold L.
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