Accurately measure the position of the linear coil motor and how does the encoder do it?
time：2017/4/1 click：7671
Linear coil motors can be used in laser cutting equipment industry, semiconductor production equipment industry, flat panel display industry, printing equipment industry, medical equipment industry, precision detection equipment industry, electronic component surface mount equipment industry, PCB detection equipment industry, logistics equipment industry and other different fields. How to control the position of linear coil motor with high precision? This is due to the encoder, but what is the encoder? How did he accurately measure the position of the motor? Let tongmao linear motor to talk about encoder.
What's an encoder?
An encoder is a device that compiles and converts signals or data into signals that can be communicated, transmitted, and stored. The encoder converts the angular displacement or linear displacement into an electrical signal. The former is called a code plate and the latter is called a ruler(grid ruler). It is a commonly used motor positioning equipment in the industry and can accurately test the angular displacement and linear position of the motor.
Classification of encoders
According to the working principle, encoders can be divided into two types: incremental and fixed.
1, incremental encoder
The incremental encoder converts the displacement into a periodic electrical signal, which is then converted into a counting Pulse, and the number of pulses is used to represent the size of the displacement.
Incremental encoders usually have three output outlets, namely phase A, phase B, and phase Z outputs. The pulse output between phase A and phase B is delayed by 1/4 cycle. According to the delay relationship, positive inversion can be distinguished. And by taking the ascending and descending edges of phase A and phase B, the frequency can be 2 or 4 times; The Z phase is a single Pulse, that is, one pulse is emitted per circle.
The grating of incremental measurement method consists of periodic bars. Location information is obtained by calculating the number of increments(measured steps) starting from a certain point. Since a fixed reference point is used to determine the position value, the circular grating code plate also has a reference rail.
2, fixed
Each position of the fixed encoder corresponds to a definite digital code, so its indication is only related to the starting and ending positions of the measurement, and has nothing to do with the intermediate process of the measurement.
A fixed encoder corresponds to a circle. Each reference angle emits a binary value corresponding to that angle. Multiple positions can be recorded and measured through an external loop device.
When the encoder is energized, the position value can be obtained immediately and read by the subsequent signal processing electronic circuit at any time. Zero operation of reference point is performed without moving axis. The fixed position information comes from the circular grating code disk, which consists of a series of fixed codes. Individual incremental track signals generate position values by subdivision, and can also generate incremental signals for selection.
The fixed position information of a single loop encoder is repeated once per turn. Multiple loops of encoders can also distinguish the position values of each lap. They have differences: in the case of incremental encoders, the position is determined by the number of pulses calculated from the zero-bit tag, while the position of the fixed encoder is determined by the reading of the output code. In a circle, the output code reading at each location is fixed, so when the power supply is disconnected, the fixed encoder is not separated from the actual position. If the power is switched on again, then the position reading is still current and valid. Unlike the incremental encoder, it is necessary to find the zero-bit mark.
III. Working principles of encoders
From a center with an axial photoelectric code disk, which has annular and dark engravings, photoelectric emission and receiving devices are read, and four groups of sine wave signals are combined into A, B, C, and D. Each sine wave has a difference of 90 degrees in phase(360 degrees relative to a week wave), reversing the C and D signals and overlaying them on the A and B phases to enhance the stable signal; Another Z-phase pulse is output for each turn to represent the zero-bit reference bit.
Since the two phases A and B differ by 90 degrees, the zero bit reference bit of the encoder can be obtained by comparing the front phase A or the front phase B to determine the positive turn and reverse of the encoder. The materials of the encoder codeplate are glass, metal, and plastic. The glass codeplate is a thin engraving line deposited on the glass. Its thermal stability is good and its accuracy is high. The metal codeplate is directly engraved with open and impassable lines and is not easy to break. However, due to the thickness of the metal, The accuracy is limited, and its thermal stability is an order of magnitude worse than that of glass. The plastic code plate is economical and its cost is low, but the accuracy, thermal stability, and life span are all poor.
Resolution-The number of open or dark lines provided by the encoder per rotation 360 degrees is called resolution, also known as resolution score, or how many lines are directly weighed, usually at 5 to 10,000 lines per rotation.
Position measurement and feedback control principles
In elevators, machine tools, material processing, motor feedback systems, and measurement and control equipment, encoders occupy an important position. The encoder uses a grating and an infrared light source to convert the light signal into a TTL(HTL) electrical signal through the receiver. By analyzing the frequency of the TTL level and the number of high levels, the encoder intuitively reflects the rotation angle or linear position of the motor.
Since the angle and position can be accurately measured, the encoder and the inverter can be formed into a closed-loop control system, which will make the control more accurate. This is why elevators, machine tools, etc. can be used so accurately.
In summary, we understand that encoders are divided into two types: incremental and fixed, according to the structure. They also convert other signals, such as optical signals, into electrical signals that can be analyzed and controlled.
The resolution of the linear encoder used in the Tongmao precision linear coil motor has a variety of choices such as 0.1 μm, 0.5 μm, and 1 μm, which can satisfy customers 'multiple choices. At the same time, it provides standard products and customer OEM products. With its research and development and manufacturing experience in the industrial field, it meets the requirements of high performance, low cost, short delivery period, and high quality.
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