Measuring and testing – Instrument mechanism or transmission
Reexamination Certificate
1999-12-02
2001-01-16
Moller, Richard A. (Department: 2856)
Measuring and testing
Instrument mechanism or transmission
C073S001750, C324S723000
Reexamination Certificate
active
06173620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angle potentiometer. More specifically, the present invention relates to an angle potentiometer provided for an angle detection unit and the like for outputting the detected angle as the duty ratio of a pulse signal.
2. Description of the Background Art
Conventionally, an angle detection unit is utilized to detect the angle of a work arm of a construction machine or the like. Since the construction machine is used out of doors, there is the problem of severe environmental changes such as temperature differences and voltage fluctuations. Thus, in the angular detection unit, a stable A/D conversion is performed that is unaffected by the temperature changes and power-supply voltage fluctuations so as to output the angle detection signal as a digital signal.
The A/D conversion portion of a conventional angle detection unit compares the voltage of the output from an angle detection sensor with the voltage of a triangular wave generated in the analog circuit including a resistance and a capacitor, varies the threshold value shaping the triangular wave, and varies the duty ratio of the logic high or “H” level to the logic low or “L” level in the output pulse.
With this method, since an analog triangular wave is generated by a resistance and a capacitor, the amplitude and the frequency of the triangular wave are caused to change due to the variations in the resistance value of the resistance and in the capacitance value of the capacitor owing to temperature changes. Consequently, the frequency of the output pulse and the duty ratio are varied. Particularly, the variation of the duty ratio has particularly proven to be a problem.
In addition, when the angle detection unit is used in an adverse environment, i. e. where water or mud is splashed over the housing of the angle detection unit, the water or mud enters the housing, often causing the output terminal and the high voltage line to become short-circuited. In such cases, a high voltage is applied to the output transistor, which leads to a possible malfunction of the output transistor or the like. As a consequence, conventionally such measures are taken as utilizing a special seal to block the water or mud from entering into the electronic circuitry of the sensor even in such an adverse environment, employing an output semiconductor device having a good voltage withstanding characteristic, and connecting a high-speed fuse in series to the output. The special seal, however, has become expensive. Moreover, the signal characteristic of the output can be degraded, and sometimes the fuse does not respond in time. As a result, such disadvantages are noted as a higher cost of the sensor unit, the output specification that is less than satisfactory, and shortened lifetime of the electronic components of the internal circuit.
Thus, the main object of the present invention is to provide an angle potentiometer which decreases the variation of the duty ratio due to the variation of the power-supply voltage and which is capable of converting a stable analog signal into a duty ratio of a pulse signal.
Another object of the present invention is to provide an angle potentiometer that prevents the lifetime of the electronic components of the internal circuit from becoming short, by disconnecting the output at a high speed when an excessive voltage is added to the output signal.
SUMMARY OF THE INVENTION
Simply put, the present invention is an angle potentiometer having provided on a fixed member a sensor for detecting the rotation angle of a rotational body to output an analog signal, and for outputting the sensor output as a duty ratio of a pulse signal, including an oscillation circuit for outputting repetitive pulse signals, a counter for counting the pulse signals from the oscillation circuit, a triangular wave generation circuit for generating a triangular wave based on the count output of the counter, and a comparing circuit for comparing the generated triangular wave signal with the analog signal from the sensor and for outputting a pulse signal having a duty ratio corresponding to the angle.
Thus, according to the present invention, the triangular wave signal and the analog signal from the sensor are compared, and a pulse signal having a duty ratio corresponding to the sensor output is output so that the amplitude of the triangular wave and the voltage of the sensor output vary with the temperature changes, thereby eliminating the changes in the duty ratio due to the variation of the power-supply voltage.
A preferred embodiment of the present invention includes a circuit for adjusting the offset value and the amplitude value of the triangular wave signal generated from the triangular wave generation circuit.
In addition, a more preferred embodiment of the present invention includes an output protection circuit for disconnecting the output of the comparing circuit from the output terminal in order to protect the comparing circuit from being damaged when an excessive voltage is applied from outside.
The output protection circuit includes an output semiconductor device for providing the output of the comparing circuit to an output terminal, a voltage regulating diode that is rendered conductive when the voltage on the output side of the output semiconductor device exceeds a certain voltage level, and a controlling transistor for rendering the semiconductor device non-conductive upon conduction of the voltage regulating diode.
In a still another aspect of the present invention, an angle potentiometer for outputting the detected angle as a duty ratio of a pulse signal consists of a housing, a rotational axis that is rotationally supported in the housing, a resistor that is provided facing the end of the rotational axis and extending in the circumferential direction in the housing, a brush attached to the rotational axis for rotating with the rotation of the rotational axis while being in contact with the resistance to output a divided voltage, a pulse output circuit for outputting a pulse signal having a duty ratio determined by the voltage divided by the brush, and an output protection circuit for disconnecting the output of the pulse output circuit from the output terminal when an excessive voltage is applied.
Thus, according to the present invention, the internal circuit of the output protection circuit is protected against breakdown upon the application of the excessive voltage.
In a more preferred embodiment of the present invention, the output protection circuit consists of an output semiconductor device for providing the output of a pulse output circuit to an output terminal, a voltage regulating diode that is rendered conductive when the voltage on the output side of the output semiconductor device exceeds a certain voltage level, and a controlling transistor for rendering the semiconductor device non-conductive upon the conduction of the voltage regulating diode.
Moreover, in a more preferred embodiment of the present invention, the pulse output circuit consists of an oscillation circuit for outputting repetitive pulse signals, a counter for counting the pulse signals from the oscillation circuit, a triangular wave generation circuit for generating a triangular wave based on the count output of the counter, and a comparing circuit for comparing the generated triangular wave signal with the voltage divided by a brush and for outputting a pulse signal having a duty ratio corresponding to the angle.
Furthermore, a more preferred embodiment of the present invention includes a circuit for adjusting the offset value and the amplitude value of the triangular wave signal generated from the triangular wave generation circuit.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3624475 (1971-11-01), Smith
patent: 4994752 (1991-02-01), Hata
patent: 608217
McDermott & Will & Emery
Moller Richard A.
NTN Corporation
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