Coded data generation or conversion – Digital pattern reading type converter – Optical
Reexamination Certificate
2000-10-25
2001-11-27
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Digital pattern reading type converter
Optical
C341S007000, C341S008000, C341S006000, C341S011000, C341S013000, C341S015000, C341S111000, C250S231130, C250S231140, C250S231150, C250S231160, C250S231170, C250S231180, C250S231120
Reexamination Certificate
active
06323786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an absolute-value encoder device capable of detecting a plurality of rotation quantities (detecting the number of revolutions), and more particularly the invention relates to an absolute-value encoder device which is driven to operate by a battery even at the power stoppage.
2. Description of the Related Art
This type of the absolute-value encoder device includes a rotary plate which rotates together with a rotary shaft. The rotary plate is provided with a light shut-off portion, such as a digital code pattern or an analog slit pattern. Light that is emitted from a light emitting element passes through the light shut-off portion, and is received by a light receiving element. As output signals of the light receiving element, two pulse signals as electrical signals (a first pulse signal, e.g., a pulse signal of phase A, and a second pulse signal, e.g., a pulse signal of phase B) are produced one pulse every complete shaft revolution. A phase difference between those two pulse signals is 90°.
FIG. 8
is a block diagram showing a conventional absolute-value encoder device. In the figure, reference numeral
66
is clock generating means, e.g., a clock forming portion, for generating a clock signal for an internal circuit. The clock forming portion
66
includes a selector
66
a
therein. The selector
66
a
selects high or low frequency of a clock signal output from the clock forming portion
66
depending on whether electric power is supplied from a main power supply (usually electric power formed by transforming and rectifying a commercial AC power is supplied) or a power supply other than the main power supply (usually supplied from a battery).
Reference numeral
60
is an LED lighting portion which turns on an LED the clock pulse is in “H” level, and reference numeral
610
is pulse signal forming means, e.g., A/B phase forming portion.
When the LED is lighted by the LED lighting portion
60
, light emitted from the LED is irradiated on a slit of an encoder disc. Light that passes through the is incident on the A/B phase forming portion
610
, which in turn forms a first pulse signal, e.g., an A-phase pulse signal, and a second pulse signal, e.g., a B-phase signal.
Reference numeral
63
is rotation-quantity counting means, e.g., a multi-rotation counter, for holding a current value representative of the number of revolutions of the shaft. When a change in the A-phase pulse signal is detected from the present clock pulse, and the B-phase pulse signal is in “H” level, the multi-rotation counter
63
performs its counting operation.
When the B-phase pulse signal is in “H” level, the multi-rotation counter
63
counts up upon detection of a leading edge of the A-phase pulse signal, and counts down upon detection of a trailing edge thereof. Those counting operations are performed when a clock pulse is received from the internal clock generator.
Also during a power stoppage or the like in which no electric power is supplied from the main power supply to the motor, it sometimes happens that external force is accidentally applied to the shaft and the shaft automatically rotates, and that the brake is accidentally released and the shaft will start to rotate by itself. To cope with such cases, the absolute-value encoder device is arranged such that its internal circuit is operated by a battery even when the main power supply supplies no electric power.
In the conventional device, in case where the electric power is supplied from the battery, to control the power consumption of the battery, as described above, the period of the clock pulse signal to drive the internal circuit is set to be long (the frequency of the clock pulse signal is set to be low). In a case that the electric power is supplied from the main power supply, the period of the clock pulse signal to drive the internal circuit is set to be short (the frequency of the clock pulse signal is set to be high).
When the clock frequency is relatively high as of a clock waveform (
2
) in
FIG. 7
in a state that the frequency of the clock pulse signal has been changed to the low frequency, the next clock pulse comes in within a period that the A-phase pulse signal has changed its level to high level (referred to as “H” level) but the B-phase pulse signal is still in “H” level. Therefore, the multi-rotation counter
63
can normally count. Where the frequency of the clock pulse signal is relatively low as of a clock waveform (
1
), even when the A-phase pulse signal changes its level to an “H” level, the clock pulse is not applied to the multi-rotation counter within the period that the B-phase pulse signal is in “H” level. Therefore, the multi-rotation counter
63
cannot count normally.
The following relation holds between a rotational speed which allows the multi-rotation counter
63
to normally count and a clock frequency.
Clock frequency (Hz)=rotational speed (number of revolution/sec)×4
Where electric power is supplied from the battery, the follow problems arise. If the shaft is rotated at high speed in excess of that in the above equation, the multi-rotation counter
63
does not count normally. As a result, the absolute-value encoder device erroneously detects a plurality of rotation quantities. Further, if the frequency of the clock pulse signal is previously set at a high frequency, the battery is fast consumed.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an absolute-value encoder device in which in the case that the electric power is supplied from a battery, its dissipation of the electric power is small and the erroneous detection of the plurality of rotation quantities is prevented, and which the device may be manufactured without great increase of the cost.
The present invention provides an absolute-value encoder device which comprises: a rotary disc rotating with a shaft;
pulse signal forming means for producing first and second pulse signals shifted about 90° from each other, each of the pulse signal being generated one pulse for each complete revolution of the shaft, based on light having passed through a light shut-off portion provided on the rotary disc, four angular segments into which angular positions of one revolution of the shaft are divided being specified by the first and second pulse signals; clock generating means for generating a clock pulse signal; and rotation quantity counting means which counts, based on the clock pulse signal, when the first pulse signal changes its logic level in a state that the second pulse signal is in a predetermined logic level, and holds the present value of the number of revolutions of the shaft; wherein when either of the two pulse signals changes its logic level, the clock generating means changes the frequency of the clock pulse signal to a high frequency. With such an arrangement, it is prevented that the encoder device erroneously detects a plurality of rotation quantities when electric power is supplied from a battery to the absolute-value encoder device. This is achieved without great increase of cost. Further, consumption of the battery is reduced.
The absolute-value encoder device further comprises number-of-clock counting means for counting clock pulses. The number-of-clock counting means is placed to a reset state at a start position of each of the four angular segments. In the decoder device, when a count value of the number-of-clock counting means exceeds a preset value, the clock generating means changes the frequency of the clock pulse signal to a low frequency. Where electric power is supplied to the encoder device from the battery, when the shaft stops or rotates at extremely low speed, the clock pulse signal becomes low in frequency. As a result, the battery consumption is further reduced.
In the absolute-value encoder device, the pulse signal forming means outputs a predetermined number of pulse signals in addition to the first and second pulse signals, the clock generating means changes the frequency of the clock
Aoki Yukio
Ohmura Yoichi
Okamuro Takashi
Sakuma Hirokazu
Satone Toshikazu
Mai Lam T.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tokar Michael
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