The types of position detection devices and where they are installed on the machine

Position detection device.

1. Classification and requirements of position detection devices.

The position detection device is an important part of the closed-loop feed servo system, and its accuracy is largely determined by the progress of the position detection device. Now, the highest level of detection elements and systems: when the maximum moving speed of the measured component is 240m min, the detection displacement resolution is 1um; At 24m min, resolution; The highest resolution is achievable.

Requirements for position detection devices:

1) It is less affected by temperature and humidity, works reliably, can maintain accuracy for a long time, and has strong anti-interference ability;

2) Within the moving range of the machine tool actuators, it can 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 measurements (the signals obtained are different).

1 Digital measurement.

The measurements are expressed numerically. The measurement signal is generally an electrical pulse, which can be directly sent to the numerical control device for comparison processing and display. Such detection devices are: grating detection device, pulse encoder. The device is relatively simple and has strong anti-interference ability.

2 Analog measurements.

To be measured is expressed as a continuous variable. For example, the amplitude change and phase change of voltage.

The amount of phase change can be directly sent to the numerical control device for comparison with the command voltage of phase shifting, and the amount of amplitude change can be converted into a digital pulse signal first, and then sent to the numerical control device for comparison and display. Such devices are: resolvers, inductive synchronizers.

2) Incremental and absolute measurements (different measurement methods).

1 Incremental measurements.

Only the increment of displacement is measured, and the number of digital pulses is used to express the number of unit displacements.

Since the distance of the displacement is calculated by the accumulation of incremental values, if a measurement is made incorrectly, the resulting displacement distance is incorrect.

Because the absolute coordinate position cannot be indicated, when the power is cut off due to an accident and the position of the executing part changes, it cannot be directly returned to the original position at the time of shutdown from the position after maintenance, but must first return to the starting position of the processing program, and calculate the distance from the starting point to the shutdown position, so that the displacement command can be used to make the executed part move back to the position when it was stopped, so as to continue processing. Light encoders, pulse encoders, resolvers, inductive synchronizers, and magnetic tapes are all incremental detection devices.

2 Absolute measurement.

It can measure the absolute coordinate value of the measured part in an absolute coordinate system and represent it as a binary or twenty-decimal digital signal. It needs to be converted into a pulsed digital signal before it can be sent for comparison and display. Yes

Absolute pulse coder disc, three-speed absolute coded disc. The structure is complex, and the resolution and displacement are limited.

In addition, depending on the installation measurement location, there are direct and indirect measurements.

The zero point of the machine tool, the limit of the machine tool. Knife setter.

1. Requirements for testing components for CNC machine tools:

The detection element is an important part of the detection device, and its main function is to detect displacement and speed, and send feedback signals. The smallest amount of displacement that a displacement detection system can measure is called resolution. The resolution depends not only on the sensing element itself, but also on the measurement circuit.

1. The main requirements of CNC machine tools for testing components are:

1) Long life, high reliability and strong anti-interference ability;

2) Meet the requirements of precision and speed;

3) Easy to use and maintain, suitable for the operating environment of CNC machine tools;

4) Low cost.

5) Easy to connect with computer.

Different types of CNC machine tools have different requirements for the accuracy and speed of the inspection system. Usually large-scale CNC machine tools mainly meet speed requirements, while medium, small and high-precision CNC machine tools mainly meet accuracy requirements. When selecting the resolution and pulse equivalence of a measurement system, it is generally required to be an order of magnitude higher than the machining accuracy.

Second, the requirements of CNC machine tools for position detection devices.

The position detection device is an important part of the servo system of CNC machine tools. The function of the position detection device is to detect displacement and velocity, send feedback signals, and form a closed-loop or semi-closed-loop control. The machining accuracy of CNC machine tools is mainly determined by the accuracy of the detection system.

Different types of CNC machines have different requirements for position detection elements, accuracy requirements for inspection systems and maximum movement speed of the measured components. The highest level of inspection components and systems is now available; When the maximum moving speed of the measured part is as high as 240m min, the resolution of its detected displacement (the smallest displacement that can be detected) can reach 1um, that is, it can be reached at 24m min. The highest resolution can be achieved.

The requirements of CNC machine tools for position detection devices are:

1) It is less affected by temperature and humidity, works reliably, can maintain accuracy for a long time, and has strong anti-interference ability;

2) Within the moving range of the CNC machine tool execution parts, it can meet the requirements of accuracy and speed.

3) Easy to use and maintain, adapt to the working environment of CNC machine tools.

4) Low cost.

51.What are the requirements for position detection devices for CNC machine tools?

2.How can position detection devices be classified?

3.What role does the position detection device play in the control of CNC machine tools?

4.The structural characteristics of the inductive synchronizer and resolver were analyzed.

5.The working principle of the inductive synchronizer working in the phase identification method and the amplitude identification method is described.

6.The working principle of the photoelectric incremental pulse encoder is described.

7.What is the function of the pulse encoder that rotates synchronously with the spindle when the CNC lathe turns the thread?

8.The working principle of the grating detection device is described.

9.What are the components of a grating displacement-to-digital conversion circuit?

10.On a horizontal CNC machining center, the displacement of the table is measured with a grating detection device, if 100 lines mm are used

How high can the resolution be achieved with the 10-octave circuit?

11.If the grating has a density of 50

Line mm, what is the angle between the two grating lines? , then what is the width of the moiré stripe?

12.What are the characteristics of flux-responsive heads?