An encoder is a device that encodes and converts signals (such as bitstreams) or data into a signal form that can be used for communication, transmission, and storage. Encoders convert angular or linear displacement into electrical signals; the former is called a code disk, and the latter a code scale. According to the readout method, encoders can be divided into contact and non-contact types; according to their working principle, they can be divided into incremental and absolute types. Incremental encoders convert displacement into periodic electrical signals, and then convert these electrical signals into counting pulses, using the number of pulses to represent the magnitude of the displacement. Each position of an absolute encoder corresponds to a specific digital code; therefore, its reading depends only on the starting and ending positions of the measurement, and is independent of the intermediate steps.
I. Main Classifications of Encoders
Encoders can be classified as follows.
1. Classified according to the different engraving methods of the code disk
(1) Incremental type : This means that a pulse signal is emitted for every unit angle rotated ( some also emit sine and cosine signals).
Then it is further subdivided (and chopped to produce higher frequency pulses ) , usually output as phase A , phase B , and phase Z. Phase A and phase B are pulse outputs that are delayed by 1/4 cycle. The forward and reverse directions can be distinguished according to the delay relationship. Moreover, the frequency can be multiplied by 2 or 4 by taking the rising and falling edges of phase A and phase B. Phase Z is a single-turn pulse, that is, one pulse is emitted per turn.
(2) Absolute value type : For each reference angle, a unique binary value corresponding to that angle is emitted. Multiple positions can be recorded and measured through an external clocking device.
2. According to the signal output type, it is divided into : voltage output, open collector output, push-pull complementary output, and long-line drive output.
3. Classification by encoder mechanical mounting method
(1) Shaft type : The shaft type can be further divided into clamping flange type, synchronous flange type and servo mounting type, etc.
(2) Bushing type : Bushing type can be further divided into semi-hollow type, fully hollow type and large diameter type, etc.
4. Encoders can be classified according to their working principle into : photoelectric type, magnetoelectric type, and contact brush type.
II. Common Encoder Faults
1. Encoder malfunction : This refers to a fault in the encoder's own components.
This can cause the encoder to fail to generate and output the correct waveform. In this case, the encoder needs to be replaced or its internal components repaired.
2. Encoder connection cable failure : This is the most common type of failure and frequently encountered during maintenance, so it should be the first factor considered. It is usually caused by an open circuit, short circuit, or poor contact in the encoder cable. In this case, the cable or connector needs to be replaced. Special attention should also be paid to whether the cable is not securely fastened, causing loosening and resulting in solder joint failure or open circuit. In this case, the cable needs to be tightened.
3. Encoder +5V power supply drop : This means that the +5V power supply is too low. It should not be lower than 4.75V . The reason for the low voltage is that the power supply is faulty or the resistance of the power transmission cable is too high, which causes losses. In this case, the power supply needs to be repaired or the cable needs to be replaced.
4. Absolute encoder battery voltage drop : This fault usually has a clearly defined alarm.
At this point, the battery needs to be replaced. If the reference point position memory is lost, a return-to-reference-point operation must also be performed.
5. The encoder cable shield is not connected or is detached : This will introduce interference signals, make the waveform unstable, and affect the accuracy of communication. It is necessary to ensure that the shield is reliably soldered and grounded.
6. Loose encoder installation : This fault will affect the position control accuracy, causing excessive position deviation during stopping and moving, and may even trigger a servo system overload alarm immediately upon power-on. Please pay special attention.
7. Raster contamination: This will reduce the signal output amplitude. The oil stains must be gently wiped away with degreased cotton soaked in anhydrous alcohol.
