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Demag encoder is a sensor that converts mechanical geometric displacement on the output shaft into pulses or digital quantities through photoelectric conversion. This is currently the most widely used sensor. Photoelectric encoders consist of a light source, an optical code disk, and photosensitive elements. The grating disk has several rectangular holes evenly distributed on a circular plate of a certain diameter. Since the optical code disk is coaxial with the motor, when the motor rotates, the grating disk rotates at the same speed as the motor. A detection device composed of electronic components such as light-emitting diodes detects and outputs several pulse signals. By calculating the number of pulses output by the photoelectric encoder per second, the current speed of the motor can be reflected. In addition, to determine the direction of rotation, the code disk can also provide two pulse signals with a phase difference of 90º.

Demag encoder principle

Magnetic encoders adopt a magnetoelectric design, using changes in the magnetic field of magnetic induction devices to generate or provide the position and speed of the actuator (servo motor). The physical working principle of magnetic encoders is the magnetoresistive effect. The magnetoresistive effect arises from charge carriers inside a current-carrying conductor or semiconductor; under the action of external Lorentz force, the trajectory of internal charge carriers deflects or produces spiral motion, thereby changing the potential difference inside the conductor or semiconductor. This process is only a microscopic manifestation; macroscopically, as long as the external magnetic field changes, the magnetoresistance value will also change accordingly. This is the magnetoresistive effect of magnetic encoders. The magnetoresistive devices in magnetic encoders include semiconductor magnetoresistive devices and ferromagnetic magnetoresistive devices. Thus, the detection probe of a magnetic encoder uses magnetoresistive devices as the magnetic head. Currently, common magnetoresistive heads for magnetic encoder probes include Giant Magnetoresistance (GMR) heads (GMR) and Anisotropic Magnetoresistance (AMR) heads (AMR). However, due to advantages such as better frequency characteristics and higher sensitivity compared to GNR heads, AMR heads are gradually becoming the mainstream application for magnetic encoders.

Demag encoder selection precautions

1) Standard form factors of absolute encoders: 38MM, 58MM, 66MM, 80MM.100MM.2) Absolute encoders are classified into: single-turn, multi-turn. 3) Bus encoders are classified by principle into: incremental absolute encoders, optical absolute encoders. 4) Bus encoder cable exit methods are classified into: side exit, rear exit. 5) Bus encoder shafts are classified into: 6MM, 8MM, 10MM, 12MM, 14MM, 25MM. 6) Bus encoders are classified into: shafted, blind hollow, through hollow. 7) Bus encoder protection ratings are classified into: IP54-68. 8) Bus encoder mounting methods are classified into: clamping flange, synchronous flange, clamping with synchronous flange, blind hollow (spring leaf, clamping), through hollow (spring leaf, key pin). 9) Absolute encoder accuracy is classified into: single-turn accuracy and multi-turn accuracy, which together constitute the total accuracy, i.e., the typical number of bits (standard 24 is, 25 is, 30 bits, 32 bits). 10) Absolute encoder communication protocol baud rate: 4800~115200 bit/s, commonly considered 9600 bit/s. Refresh cycle approximately 1.5ms. Encoder output options include: SSI, 4-20MA, profibus-dp, DEVicenet, parallel, binary code, BESM58, BiSS, ISI, CANopen, Endat, and Hiperface.

Demag encoder troubleshooting

Encoder internal fault: refers to a failure of the encoder's own components, causing it to fail to generate and output correct waveforms. In this case, the encoder needs to be replaced or its internal components repaired. Encoder connection cable fault: This fault occurs most frequently and is often encountered during maintenance; it should be the primary consideration. It is usually caused by open circuits, short circuits, or poor contact in the encoder cable, requiring replacement of the cable or connector. Special attention should be paid to whether loose cable fixation causes loosening, leading to open solder joints or open circuits; in this case, the cable needs to be secured tightly. Encoder +5V power supply drop: refers to the +5V power supply being too low, typically not lower than 4.75V. The cause of low voltage is usually a power supply fault or excessive resistance in the power transmission cable causing loss; in this case, the power supply needs to be inspected or the cable replaced. Absolute encoder battery voltage drop: This fault usually triggers a clear alarm; the battery needs to be replaced. If the reference point position memory is lost, a return-to-reference-point operation must be performed. Encoder cable shield wire not connected or detached: This introduces interference signals, making the waveform unstable and affecting communication accuracy. Reliable welding and grounding of the shield wire must be ensured. Loose encoder installation: This fault affects position control accuracy, causing excessive position deviation during stopping and movement, or even triggering servo system overload alarms immediately upon startup. Please pay special attention. Grating contamination: This reduces signal output amplitude. Oil stains must be gently wiped off with degreasing cotton soaked in anhydrous alcohol.

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