Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-12-20
2001-05-22
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C700S013000, C700S186000
Reexamination Certificate
active
06236325
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position detector that employs a scale unit having a linear encoder and so forth. The present invention relates more particularly to a position detector having a function capable of detecting irregularities, such as a failure in the encoder and a break in a cable, and cable for use in the detector.
2. Description of the Related Art
In a positioning device for a machine tool and semiconductor manufacturing equipment, output signals from a scale unit having a linear encoder can typically be employed as position feedback signals for a controller. The position signals from the linear encoder to the controller may often be transmitted in the form of differential signals with A/B/Z phases on the basis of RS422A. The conventional controller has the following functions for detecting irregularities of the outputs from the linear encoder;
(1) A function for detecting a break and poor connection in a cable between the output of the encoder and the input of the controller; and
(2) A function for detecting an irregularity in the output value from the encoder.
With respect to (1), detecting a high-impedance state of the controller input can perform the irregularity detection. As for (2), detecting if a deviation between position instruction information and position feedback information from the scale unit (encoder) is an abnormal value can perform the irregularity detection. Some controllers may not have the function (2). In those cases, an irregularity detecting circuit is provided inside the scale unit for diagnostic checks on itself. The circuit varies its output to a high-impedance state when an irregularity occurs so that the controller can detect the irregularity of the encoder output.
The above irregularity detection method for the conventional position detector, however, has such a disadvantage that the controller can not determine whether the high-impedance state detected is caused from a break in the signal cable or an output irregularity of the encoder in the scale unit. This makes it difficult to perform a fast procedure at the time of maintenance.
A system has also been known, which has an indication function for indicating an irregularity state in a pulse unit that is arranged separately from the scale unit. The pulse unit for use in this system converts analog signals supplied from an encoder, such as bi-phase pseudo-sinusoidal wave signals, into bi-phase rectangular wave signals with a required resolution at an interpolation circuit. The pulse unit outputs position pulse signals with A/B/Z phases to the controller through a driver corresponding to RS422. In addition, the pulse unit detects if any irregularities occur in the level of the encoder signal and the state of the interpolation circuit. When an irregularity occurs, the pulse unit varies its output for the controller to a high=impedance state and at the same time discriminates the irregular phenomenon to indicate it on a display.
The system using such the pulse unit is excellent in maintainability, however, it also has a disadvantage that the pulse unit prevents the space and cost from reducing because it must be arrange between the scale unit and the controller but is an separate unit from them. There is another system that contains the above-described function of the pulse unit inside a scale unit for the purpose of reducing the space and cost. In this case, the scale unit may often be mounted on a periphery of a movable element of the positioning device. Therefore, it is difficult to confirm an indicator by human eyes and thus such the indicator can not be employed. As a result, an irregular state can not be identified and a rapid procedure at the time of maintenance can be hardly achieved.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of such the disadvantages and accordingly has an object to provide a position detector with an irregularity detectable function and cable for use in the detector. The position detector can achieve a rapid procedure at the time of maintenance along with sustaining the reduction of space and cost.
The present invention is provided with a position detector, which comprises a scale unit including a stationary element and a movable element. The scale unit generates position pulses in accordance with a relative displacement between the stationary element and the movable element. The scale unit outputs the position pulses via a first cable having a first connector at an end position thereof. The position detector also comprises a controller for position detecting. The controller receives the position pulses from the scale unit via the first cable. The controller calculates a relative position of the movable element to the stationary element based on the received position pulses. The scale unit generates an alarm signal to notify an error associated with generating the position pulses when the error occurs. The first cable transfers the alarm signal to the first connector. The first connector contains an irregularity informing means for performing an irregularity informing operation in response to the alarm signal output from the scale unit.
The present invention is also provided with a scale unit, which comprises a stationary element, a movable element, and a first cable having a first connector at an end portion thereof. The scale unit generates position pulses in accordance with a relative displacement between the stationary element and the movable element. The scale unit outputs the position pulses via the first cable. The scale unit generates an alarm signal to notify an error associated with generating the position pulses when the error occurs. The scale unit transfers the alarm signal to the first connector. The first connector contains an irregularity informing means for performing an irregularity informing operation in response to the alarm signal output from the scale unit.
The present invention is further provided with a cable for use in a position detector. The cable has a connector section at an end portion thereof. The cable transfers, to another equipment, position pulses generated at a scale unit in accordance with a relative displacement between a stationary element and a movable element. The cable comprises an alarm signal wire for transferring an alarm signal output from the scale unit to notify an error when the error occurs associated with generating the position pulses at the scale unit. It also comprises an irregularity informing means contained in the connector section for performing an irregularity informing operation in response to the alarm signal transferred via the alarm signal wire.
In the present invention, the scale unit has a function for generating an alarm signal to notify an irregularity associated with generating the position pulses when the irregularity occurs. The alarm signal is conducted to the first connector thorough the first cable elongated from the scale unit to operate the irregularity informing means contained within the first connector. Therefore, when the controller detects the irregularity, it is possible based on a situation of the irregularity informing means to identify which one has occurred between an error due to position pulse generation within the scale unit and an error due to a break or poor connection in the cable. In addition, the irregularity informing means can be dispose at an optimal location to be confirmed easily by human eyes because it is accommodated inside the first connector at the end portion of the first cable. Further, the present invention does not employ an additional separate unit such as the pulse unit, possible reducing the space and cost.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.
REFERENCES:
patent: 4118690 (1978-10-01), Paynton
patent: 4494206 (1985-01-01), Imazeki et al.
patent: 5034877 (1991-07-01), Shultz
patent: 5051579 (1991-09-01), Tsukiji et al.
patent: 5406267 (1995-04-01), Curtis
Kawada Hiroaki
Kuroki Shingo
Yamaguchi Yasuo
Hofsass Jeffery
Mitutoyo Corporation
Oliff & Berridg,e PLC
Tang Son
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