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Precision Position Feedback DetectorーGeneral

Precision Position Feedback Detector

General

Mitsubishi Precision Scale (MP SCALE) is a non-physical contact, ultra-precision position detector used for detecting linear or angular position utilizing the inductive coupling principle.
The manufacture and sale of MP Scale has been started under the technical cooperation with INDUCTOSYN Co. in U.S. since 1970.

Full closed control composition
Full closed control composition

MP Scale detects the amount of movement of a machine and outputs an analog signal. This signal is converted into a digital signal by an A/D converter and fed back to the NC system.
Thus the machine can be controlled accurately by the fully closed-loop NC system based on the position feedback data from MP SCALE.

Note) Full closed-loop NC system :The control method which detects the last position (or angle) of the machine by Scale, and return detected data to NC equipment in order to move the machine to the target position (or angle).

Linear Feedback Detector
Linear Position detector(Linear MP Scale)
Linear Position detector(Linear MP Scale)

Slider of Linear MP Scale is mounted on the movable part, and Scale is mounted on the fixed part. The position of the linear axis is detected with high precision by Linear MP Scale.

Rotary Feedback Detector
Rotation angle detector(Rotary MP Scale)
Linear Position detector(Linear MP Scale)

Rotor of Rotary MP Scale is mounted on the rotation shaft of the rotating axis like the rotary table or the angle head, and Stator is mounted at the fixed part. The rotation angle is detected with high precision by Rotary MP Scale.

Application

5-axis machining on the rotary table

Highly precise 5-axis machining is attained by mounting Rotary MP Scale on the rotary table of 5-axis machine.

5-axis machining utilizing a rotary table
5-axis machining utilizing a rotary table
5-axis machining utilizing a rotary table
5-axis machining utilizing a rotary table
Supermiller(World largest class machine tool)
Gantry, longitudinal
(Synchronized)
X axis 32.5m
Saddle, left/right Y axis 12.7m
Ram, up/down Z axis 3.5m
Cross-rail, up/down W axis 7.0m
Supermiller(World largest class machine tool)
Supermiller(World largest class machine tool)

X-axis (32.5m) of the supermiller (the world largest class machine tool) is also equipped with Linear MP Scale.

5-axis angle head and large-sized precision positioning table
5 axis angle head
5 axis angle head

Rotary MP Scale are mounted on B axis and C axis of 5-axis angle head, and highly precise 5-axis machining is possible.

Large-sized precision positioning table of the manufacture equipment for LCD and PDP.
Large-sized precision positioning table of the manufacture equipment for LCD and PDP.

Rotary MP Scale is used for the large-sized precision positioning table of the manufacture equipment for LCD and PDP.

Linear axis and rotary axis of Multi-tasking Lathe
Linear and rotary axis of Multi-tasking Lathe
Linear and rotary axis of Multi-tasking Lathe
  1. The highly precise curve machining is possible by mounting Rotary MP Scale for the control of spindle speed and C axis positioning, and mounting Rotary MP Scale also for B axis positioning for the tool tilt.
  2. Mounting Linear MP Scale in X-axis and Y-axis with few spaces is possible. This mounting is effective for the heat expansion of the ball screw.

Principle

Inductive coupling action
Inductive coupling action
  1. The induction pattern, in the rectangular form, is printed on both Slider and Scale in the Linear type and Stator and Rotor in the Rotary type MP Scale.
  2. When the alternating current is fed to the Slider(Stator) patter, the voltage is energized to the Scale(Rotor) pattern due to the inductive coupling action.
  3. The energized voltage will vary as the relative position of Scale (Rotor) and Slider (Stator) changes. The position of the machine is detected based on the variation of this voltage.
Change in degree of inductive coupling due to the relative position of Slider and Scale
Degree of inductive coupling due to the relative position of Slider and Scale
Degree of inductive coupling due to the relative position of Slider and Scale
  1. At position A, the degree of the inductive coupling is the maximum in the positive direction as the patterns of both Slider and Scale coincide with each other.
  2. At position B, where Slider is shifted by 1/4 of a pitch relative to the Scale pattern, the current that that flows in the both directions of Slider cancels out the flow in Scale, thus nullifying the degree of the inductive coupling.
  3. At position C, where Slider is shifted by 1/2 of a pitch to the Scale pattern, the situation becomes reversed to that of position A, thus degree of the induction coupling becomes maximum in the negative direction.
  4. At position D, where Slider is shifted by 3/4 of a pitch relative to the Scale pattern, the situation becomes similar to that of position B, thus nullifying the degree of inductive coupling.
  5. At position E, where Slider is shifted by 1 pitch relative to the Scale pattern, the situation becomes same as that of position A.
Actual pattern of Slider
2 patterns in Slider
2 patterns in Slider

Slider comprises two patterns set at 1/4 a pitch apart. This enables generation of the sine and cosine curve inductive coupling.
The extremely precise position detection is made possible without any effect of in the difference of the gap between Scale and Slider as Slider moves along the applied axis.

Features

Features of Linear
Features of Linear
Features of Rotary
Features of Rotary
High accuracy
High Accuracy
Features of Rotary
Features of Linear
Actual data of MPI-1272B
Actual data of MPI-1272B

The guarantee accuracy of Linear MP Scale MPS-25CSC is 2 μm and the guarantee accuracy of Rotary MP Scale MPI-1272B is 2 seconds.
Note) The description of all accuracy is shown as the width of the error.

High-resolution/High-speed
High Resolution
High Speed
Features of Rotary
Features of Linear
Linear/Rotary Interface Resolution Speed
Linear detector
(Linear MP Scale)
A,B,Z Phase Pulse 0.1 μm 80 m/min
Serial interface 0.01 μm 1,800 m/min
Rotary detector
(Rotary MP Scale)
A,B,Z Phase Pulse 0.0001 deg. 222 min-1
Serial interface 223 / rev (0.000043deg.) 10,000 min-1

Note) Above data is typical.

Direct detection
Direct Detection
Features of Rotary
Features of Linear

There is no effect of the ball screw expansion as Scale is mounted to the final moving element of the machine.

Direct detection

Direct detection

Unaffected by dust, oil, and condensation
No Air Purge
Features of Rotary
Features of Linear

Due to the adoption of electromagnetic inductive detection method, the position can be detected without influence from oil contamination , dust, and condensation in the gap between Slider and Scale. Air purge is unnecessary.

Example of Scale used for 7 years

Example of Scale used for 7 years
Even if cast powder and oil adhere, it continues to operate satisfactory.

Small mounting space
Small mounting space
Features of Rotary
Features of Linear
  • Thin: Only 14-20 mm thick
  • Since Rotary MP Scale has the center hollow, the wiring and piping can be passed in this hollow in the case of 5-axis head.
Sum total thickness of Scale and Slider is about 20mm.
Non-contacting Stable high accuracy lasted for a long period
Stable for a long time
Features of Rotary
Features of Linear

MP SCALE will last for years without any deterioration in accuracy because of its non-physical contact design that eliminates any bearing or spring.

MP Scale and General glass scale
Absolute feedback system
Absolute feedback system
Features of Rotary
Features of Linear

By combining the absolute battery-back-up encoder mounted on the feed motor, the NC system provides the method in which the encoder detects the rough absolute position and the MP Scale detects the fine position.
(Offset absolute system)

Absolute system combined motor encoder

Absolute system combined motor encoder

Absolute value Rotary MP Scale MPRZ
Absolute value Rotary MP Scale MPRZ

MPRZ series detects the absolute value using an independent Scale. Highly suitable for detector of DD motor.

Various NC interface
CNC
Features of Rotary
Features of Linear

A/D converter can be connected to NC system built by MITSUBISHI CNC, FANUC, SIEMENS, and AC servo BY MITSUBISHI, and YASKAWA ΣV & Σ7.
SSI communication is applicable as general code for serial interface.

Connectable to various NC interface

Connectable to various NC interface

High repeatability
Repeatability
Features of Rotary

Eccentricity often occurs according to the shaft movement by the difference in the rotation direction or the eccentric work road. With MP SCALE, eccentricity does not cause big detecting error and high repeatability is acquired.

Since conventional other scale has one detecting head, the detecting error is in proportion to the quantity of eccentricity, and the repeatability is bad.
As conventional countermeasure to this eccentricity on scale, two detecting heads are mounted into he opposite position and the detecting error is canceled by two heads.
On MP Scale, by arranging many detecting patterns all over the circumference, the error by the eccentricity is canceled and the high repeatability is acquired.

General one head Scale・General countermeasure to eccentricity・MP Scale

General one head Scale・General countermeasure to eccentricity・MP Scale

High accuracy machining is possible, since heat expansion of Scale is same as iron.
Against heat
Features of Linear

Example) Even if machined at 17℃, directed dimension is realizable at 20℃.

High accuracy machining is possible, because heat expansion of Scale is same as iron.