Measurement Principles
A/B phase difference output
(90° phase difference output)
The amount of rod movement in the scale cylinder is detected
using an MR element (magnetic resistance element) whose
resistance value changes due to magnetic force. The detection
unit containing this MR element is called the sensor head. An
amplifying circuit and a dividing circuit are required to produce
output which can be read by the counter, and these are attached
to the cylinder case. The sensor head and amplifier section
together are referred to as the sensor unit.
(1) A scale of magnetic layers and non-magnetic layers with a
pitch of 0.8mm is cut into the piston rod.
(2) With movement of the piston rod, a sin, cos 2-phase signal
(Signal 1) is received by the magnetic resistance element.
For this wave form, 1 pitch (0.8mm) becomes exactly 1 cycle.
(3) This is amplified and divided into 1/8 parts. As a result, a 90°
phase difference pulse signal of 0.1mm/pulse (Signal 2) is
output.
(4) By measuring this pulse signal with the counter, it is possible
to detect the piston position with a resolution of 0.1mm.
(5) In the case of the high precision scale cylinder, the sin, cos 2-
phase signal obtained in (2) is amplified and divided into 1/20
parts. As a result, a 90° phase difference pulse signal of
0.04mm/pulse (Signal 2) is output.
(6) By multiplying this pulse signal by 4 with the counter, it is
possible to detect the piston position with a resolution of
0.01mm.
The scale cylinder is equipped with the capability of outputing the
piston stroke movement as a pulse signal. The measurement
principle is as shown in the drawing below.
When movement is expressed by a single line of pulses, it is
impossible to accurately identify the current position, because
pulse waves appear in both upward and downward directions.
Accordingly, in A/B phase difference output, two lines of pulses
are provided, wherein one line detects the movement and the
other distinguishes the direction.
4 times multiplication function
A phase
B phase
Count 1 2 3
This function increases resolution 4 times by counting 4 for each
cycle of pulses, instead of counting 1 for each cycle as is
normally the case. In principle, this function counts each time
there is a rise or fall in either of the A or B phase pulses.
A phase
B phase
Count 1 2 3 4 5 6 7 8 9 10 .....
Counting speed (kHz, kcps)
Counting speed indicates the number of pulses that can be
counted per second. If the scale cylinder is operated at high
speeds, pulse waves are output in shorter cycles. The counting
speed of the counter must be higher than the pulse speed for the
maximum piston speed when operating. Since the scale cylinder
outputs one pulse for each 0.1mm of movement, 5,000 pulses
will be output for each 500mm of movement. Therefore, a speed
of 500mm/s is equivalent to 5kcps (kHz), but a counting speed 2
to 3 times greater is recommended for actual operation.
Accuracy
The accuracy is the difference between the dimensions based
upon the signals of the scale cylinder and the absolute
dimensions.
The maximum display error that will appear on the counter's
digital display is equal to twice (± 1 count) the resolution when
the home position is reset and when dimensions are measured.
0.2
0.1
0.3
Sensor unit
Amplifier section
Sensor head
Magnetic scale
Cylinder section
1
Signal 1
Signal 2
2
Pitch output
Piston rod
Magnet
Magnetic
resistance
element
Amplification/
Interpolation
circuit
Counter
Magnetic section
A phase
Movement
B phase
Pitch
Non-magnetic
section
Applications
Detection of die assembly's
deceleration point
Since the deceleration point of the die
assembly can be set at will, it can be
easily changed after replacement of
the die assembly.
Length/breadth discrimination
Straightening of work piece positions is
performed at the same time that
longitudinal or transverse orientation
is distinguished.
Inspection of machined holes
Can detect machined hole depth,
burrs and foreign matter, etc.
Measurement of dimensions
Can measure dimensions of parts. Measurement of
machining dimensions
Nozzle height adjustment
Performs adjustment of machining
depth, etc. by measuring the part
dimensions before machining.
Maintains a constant height of
the nozzle from the work
piece by measuring the
work piece height.
Detection of lifter position
Can continuously monitor a
lifter's stroke.
Discrimination of direction
Direction can be discriminated by
measuring work piece height.
Confirmation of press-in
Can confirm the press-in of a
hydraulic cylinder by detecting its
stroke.
Even if the size of the work piece
changes, the point of press-in
completion can be easily changed.
Parts inspection
Measures part dimensions,
discriminates between good and
defective articles, and prevents
the mingling of different parts,
etc.
Counter
