Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
2003-01-10
2004-08-03
Barlow., John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
C324S662000
Reexamination Certificate
active
06772087
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to an absolute position measuring device. More particularly, the present invention relates to an absolute position measuring device for measuring the position of a spindle in absolute format in a micrometer head, a micrometer, or a hole test, for example.
2. Description of the Related Art
In the small measuring instruments for measuring the length, size or angle, for example, the micrometer and the micrometer head, a measurement object is measured by detecting the information as to the relative movement amount of a movable member to a fixed member.
The methods for measuring the relative movement amount of the movable member to the fixed member include the increment type, which the present applicant has disclosed in Japanese patent examined publication No. Hei. 3-79647, and the absolute type.
The former comprises a fixed member, a movable member provided movably with respect to the fixed member, and an electrostatic capacity sensor for sensing the phase of a period signal that is originated according to the movement of the movable member. In this constitution, if the movable member is moved, a phase signal periodically changing with respect to the movement amount of the movable member (spindle) is sensed by a displacement sensor, as shown in FIG.
10
. By counting the variation amount of this phase signal, the movement amount of the movable member is calculated from the relationship between the movement amount of the movable member and the phase period.
The latter involves sensing a plurality of phase signals having different periods that are originated according to the movement amount of the movable member. In this constitution, if the movable member is moved, two or more phase signals having different periods are sensed, so that the absolute position of the spindle is measured from the phases of those phase signals.
For example, a phase signal of long period (non-dense phase signal) and a phase signal of short period (dense phase signal) are sensed. Then, the positions at which the non-dense phase signal and the dense phase signal are situated in one period are obtained via the electric circuits (phase conversion circuit, interpolation circuit, etc.). From the relationship between these phases, at what periodicity the phase of dense phase signal takes place in the periods of the non-dense phase signal is calculated. From this result, the upper digits are calculated from the phase of the non-dense phase signal, and the lower digits are calculated from the phase of the dense phase signal. The calculated upper digits and lower digits are weighted and synthesized.
Herein, the method for specifying the periodicity that the phase of dense phase signal takes place in the periods of the non-dense phase signal involves dividing the phase of non-dense phase signal by the number of periods (steps) of the dense phase signal contained in one period of the non-dense phase signal.
Another method involves calculating the lower digits from a counting pulse obtained by counting a phase difference between the dense phase signal and the reference signal originated separately and synthesizing those lower digits with the upper digits obtained from the non-dense signal.
However, the increment type had the following problems.
(1) Since it is necessary to count a phase signal originated by the movement of the movable member, the device must be always in a counting state, while the movable member is being moved. Also, if the movable member is moved fast, the phase signal is changed at high rate, whereby the counting response rate must be increased to count this phase signal changing at high rate.
(2) Once a counting error occurs and if the user does not become aware of this error, a measurement error occurs. For correct measurement, the reference position of the movable member must be reset (zero set).
(3) Once the power is turned off, the reference position of the movable member must be set again when in use at the next time.
Also, the absolute type had the following problems.
(4) Though it is necessary to detect a phase difference between the non-dense or dense phase signals precisely, it is difficult to assure the precision of phase detection over a wide range. To calculate the absolute position, it is required to have a process for calculating where the dense phase signal is located in the periods of the non-dense phase signal by the logical operation for the phase signals having different periods, weighting each period, and synthesizing the phase signals, with the very complex operation steps.
(5) Besides, the method for counting the counting pulse with respect to the reference signal needs a synchronous modulation control, which is very intricate. To increase the measurement precision, it is possible to utilize the signals of three different modes of non-dense, intermediate and dense. However, the data processing is so complex that the display of data does not often follow the fast movement of the movable member. If the data processing is tried to make at high speed, the data processing unit is obliged to increase in size, resulting in a problem that this method is unsuitable for the measuring instrument of hand tool type.
SUMMARY OF THE PRESENT INVENTION
The present invention has been achieved to solve the above-mentioned problems associated with the related art. It is an object of the present invention to provide an absolute position measuring device that can detect the absolute position correctly with a smaller size of the device and a simple constitution.
In order to accomplish the object above, the following means are adopted. According to a first aspect of the present invention, there is provided an absolute position measuring device comprises:
a main body;
a movable member provided movably in the main body;
a phase signal originating section for originating two or more phase signals of different periods in accordance with an amount of movement of the movable member; and
an arithmetical operation section for making an arithmetical operation on the phase signals to obtain an absolute position of the movable member, the arithmetical operation section including a phase signal processing section for comparing the phase signals to obtain a phase difference between the phase signals, and an absolute position calculating section for calculating the absolute position of the movable member from the phase difference obtained by the phase signal processing section,
wherein the two or more phase signals have different phase differences at different positions of the movable member in a movable area of the movable member.
With this constitution, if the movable member is moved, a phase signal having a different period is originated from the phase signal originating section, and the arithmetical operation section makes the arithmetical operation on this phase signal. At this time, the phase signal originated by the phase signal originating section is firstly processed by the phase signal processing section in the arithmetical operation section to obtain a phase difference. Since this phase difference is varied at a different position of the movable member, the absolute position of the movable member can be uniquely obtained from the phase difference. Thus, the absolute position of the movable member is calculated on the basis of the phase difference obtained by the phase signal processing section by the absolute position calculating section. This absolute position is displayed in digital format by the display section, whereby the absolute position of the movable member can be known.
In related art, the upper digits were obtained by calculating the periodicity that the dense signal is located in the periods of the non-dense signal through the arithmetical operation on the non-dense and dense phase signals. Furthermore, the lower digits were obtained from the dense signal, and the upper and lower digits were synthesized. However, with this invention, the absolute value can be uniquely obtained from the phase
Barlow. John
Mitutoyo Corporation
Oliff & Berridg,e PLC
Sun Xiuqin
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