Talking about the resolution and precision of servo encoder

For linear encoders, the engraved line and the expansion of the mounting surface caused by temperature will also affect the accuracy of the encoder. The consistent width and measurement gap are the key factors affecting the accuracy of the incremental encoder.

For servo control systems, encoders with speed feedback and position feedback are required. When selecting an encoder, we must not only consider the type of encoder, but also consider the interface, resolution, accuracy, protection level and other aspects of the encoder. Meet the user's control requirements. Especially the resolution and accuracy of the encoder are closely related to motion control. Today we will talk about the resolution and accuracy of the servo encoder.

Resolution

Resolution refers to the distance generated between each counting unit of the encoder, which is the smallest distance that the encoder can measure.

For rotary encoders, the resolution is generally defined as the unit or pulse measured by one revolution of the encoder (eg, PPR). For linear encoders, the resolution is often defined as the distance between two quantization units, usually given in micrometers (μm) or nanometers (nm).

The resolution of an absolute encoder is generally defined in the form of bits, because the output of an absolute encoder is a binary "word" based on the actual position of the encoder. One bit is a binary unit, such as 16 bits equals 216, or 65536. Therefore, a 16-bit encoder provides 65536 quantization units per revolution.

Accuracy

Accuracy is used to measure the value of the repeatable average deviation between the actual value and the set value under normal conditions. For rotary encoders, it is generally defined as arc seconds or arc minutes, and for linear encoders, the accuracy is general Is micron.

An important point to note is that high resolution does not mean high accuracy. For example, two rotary encoders with the same precision, one has a resolution of 3600 PPR, and the other has a resolution of 10000 PPR. The low-resolution encoder (3600 PPR) can provide a measurement distance of 0.1°, while the high-resolution encoder can provide a smaller measurement distance, but the accuracy of the two is the same, the high-resolution encoder is only It has the ability to reduce 0.1° to a smaller incremental distance.

Encoder|Transmitter|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

Encoder resolution and accuracy are two independent concepts. As shown in the figure above, the two encoders have the same resolution (24PPR) but different accuracy.

When we discuss accuracy, we generally involve another encoder performance index-"repeatability". Accuracy refers to the degree of closeness between the measured value and the true value. Without comparing with the standard, the accuracy is impossible to talk about. "Repeatability" refers to the ability to reproduce the same result without changing the external state. In some cases, "repeatability" may be more important than accuracy. This is because if the system is repeatable, the error can be cancelled by compensation. Generally speaking, the repeatability of the encoder is defined as the multiple of the encoder accuracy, which is usually 5 to 10 times the encoder accuracy value.

Below we use a picture to feel the relationship between the three:

Encoder|Transmitter|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel. Encoder|Transmitter|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

When we usually discuss accuracy, we often combine "precision" and "repeatability" into one, and we often think that accuracy is more inclined to be expressed by "fidelity". When we talk about accuracy, we often mean "high precision with high repeatability."

Factors affecting the resolution of the encoder

Encoder|Transmitter|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

For encoders using sin/cos signals, compared to square wave signals, we can subdivide the electrical signal by θ to provide higher resolution, as shown in the figure below.

Encoder|Transmitter|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

Factors affecting encoder accuracy

1) Direction deviation of radial grating

2) The eccentricity of the marking code disc relative to the bearing

3) Bearing radial deviation

4) Error caused by the connection with the coupling

But for the Siemens servo motor encoder using HTL or TTL type, the resolution can only be increased by 4 times. For example, 1024 SR or 2048 SR type encoder, the highest resolution that can be provided is 4096 or 8192, the smallest unit that the encoder can describe after conversion is 5.27 arc minutes or 2.63 arc minutes, but its physical accuracy can provide up to ±1 arc minutes , The accuracy provided by the resolution is less than the actual physical accuracy of the encoder.

Encoder|Transmitter|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

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