A, position detection device classification and requirements

Position detection device is an important part of the closed-loop feed servo system, its accuracy is largely determined by the progress of the position detection device. Now, the highest level of detection components and systems: the highest moving speed of the measured component 240m/min, detection displacement resolution of 1um; 24m/min, resolution of 0.1um; the highest resolution of up to 0.01um.

Requirements for the position detection device:

1) subject to the temperature, humidity has little effect, reliable operation, can maintain long-term accuracy

2) in the moving range of the machine tool components to meet the requirements of precision and speed;

3) easy to use and maintain, adapt to the working environment of the machine tool.

4) Low cost.

(A) digital and analog measurement (the signal obtained by different)

1. digital measurement

The measured is expressed in digital form. Measurement signals are generally electrical pulses, can be sent directly to the numerical control device for comparison and display. Such detection devices are: grating detection devices, pulse encoder. The device is relatively simple, strong anti-interference ability.

2. Analog measurement

The measured continuous variable. Such as: voltage amplitude change, phase change. Phase changes in the amount can be sent directly to the CNC device and phase shift command voltage comparison, the amplitude of the amount of change, can be converted to digital pulse signals, and then sent to the CNC device for comparison and display. Such devices are: resolver, induction synchronizer.

(B) incremental and absolute measurement (different measurement methods)

1. incremental measurement

Only the incremental displacement is measured, and the number of digital pulses is used to indicate the amount of displacement per unit.

Since the distance of displacement is obtained by accumulating the incremental values, once the measurement is wrong at a certain place, the distance of displacement obtained thereafter will be wrong.

Because the absolute coordinate position cannot be indicated, when the position of the actuator changes due to an accidental power failure and shutdown for inspection, the actuator cannot be returned to the original position at the time of shutdown directly from the position after maintenance, but has to be returned to the starting position of the machining program and the distance from the starting point to the shutdown position has to be calculated before the displacement instruction can be used to move the actuator back to the position at the time of shutdown so that machining can be resumed. Optical encoders, pulse encoders, resolvers, induction synchronizers, and magnetic scales are all incremental detection devices.

2. Absolute measurement

Can measure the measured parts in an absolute coordinate system in the absolute coordinates of the value, and in binary or binary digital signals. Need to be converted into a pulse digital signal to be sent to the comparison and display. There are: absolute pulse coding disk, three-speed absolute coding disk. Complex structure, resolution and displacement are limited.

In addition, according to the installation of the measurement position, there are direct and indirect measurement.