LTi Synchronous Motor LST/LSH Replacement Selection Guide

LTi Synchronous Motor LST/LSH Replacement Selection Guide

Overview of LT Synchronous Motor Series

LT (LTi DRiVES) synchronous servo motors are divided into two series: LST and LSH, covering a continuous torque range from 0.1 Nm to 115 Nm. They are widely used in machine tools, packaging, printing, robots, automated production lines, and other applications that require high dynamic response and precise position control. The LST series adopts conventional winding technology and is a 6-pole synchronous servo motor suitable for applications with speeds up to 9000 rpm. It has high overload capacity and optimized moment of inertia. The LSH series provides higher torque density under the same chassis size, suitable for scenarios that require greater torque but limited installation space.

The machine base numbers range from 037, 050, 074, 097, 127, 158, 190 to 220, and the numbers represent the measured dimensions of the motor (in millimeters), not the flange dimensions. Each machine base has different overall lengths (2, 3, 4, 5) and rated speeds (30 corresponds to 3000 rpm, 45 corresponds to 4500 rpm). The DC bus voltage of the controller can be selected as 320 V or 560 V, which directly affects the rated current and back electromotive force constant of the motor. For example, LST-127-2-30-560 represents a 127 machine base, length 2, rated speed of 3000 rpm, and DC bus 560 V.

The complete format of the order code is: LSX-074-1-30-560/Options. Among them, LSX represents LST or LSH; 074 is the edge measurement dimension; 1 is the overall length; 30 is the rated speed multiplied by 100; 560 is the DC bus voltage of the controller; After the slash is the option code, such as T0, T1, T4, B, P, X, K, S4, 1R, V, W, etc. The standard configuration includes a smooth shaft (keyless), a 1-pole rotary transformer, IP64 protection (excluding flanges), IP54 overall protection, direct output plug, and dual basic insulation. Common options include: T0 thermal protection constant temperature switch, T1 dual basic insulation DIN-PTC (standard), T4 KTY84-130, B 24 VDC holding brake, P keyway, X customized design, K 1-meter cable, S4 rotatable plug, 1R 1-pole rotary transformer, V IP65 without radial seal, W IP65 with radial seal (length increased by about 10mm).

Technical data and selection points

When selecting, the first step is to determine the continuous torque, peak torque, and maximum speed required for the load. Taking the LST-127 series as an example, at a rated speed of 3000 rpm on a 560 V DC bus, the rated torque for different lengths is as follows: length 1 is 5.7 Nm, length 2 is 8.8 Nm, length 3 is 11.0 Nm, length 4 is 14.0 Nm, and length 5 is 17.0 Nm. The locked rotor torque is 6.6, 10.5, 13.5, 17.0, and 22.0 Nm, respectively. The peak torque can reach 19.8, 32, 41, 51, and 66 Nm. The rated current ranges from 4.0 A to 13.0 A. Users need to choose the appropriate length based on the continuous torque and acceleration torque of the actual load, while leaving sufficient overload margin.

For the LST-158 series, at 560 V and 3000 rpm, the rated torque for lengths 1 to 5 is 13.0, 17.0, 19.0, 24.0, 26.0 Nm, the locked rotor torque is 13.5, 19.0, 22.0, 29.0, 35.0 Nm, and the peak torque is 47, 67, 77, 102, 105 Nm. The LST-190 series provides rated torque of 21, 23, and 26 Nm, with peak torque of 81, 96, and 120 Nm. The LST-220 series provides rated torque of 30, 50, 60, and 50 Nm, with peak torque of 120, 204, 279, and 345 Nm, suitable for high-power applications.

When selecting, attention should also be paid to the DC bus voltage. The 320 V system is typically used for low-voltage servo drives, while the 560 V system is used for drives powered by standard 400 V AC. If the original motor uses 320 V, it cannot be directly replaced with a 560 V motor unless the driver supports it and the parameters are reset. The rated speed should also be matched, as motors at 3000 rpm and 4500 rpm have different currents at the same torque. In addition, the back electromotive force constant Ke, torque constant Kt, winding resistance, and inductance of the motor all affect the current loop and speed loop parameters of the driver, and usually require recalibration after replacement.

Encoder Options and Compatibility

LT synchronous motors can be equipped with multiple encoders to meet different precision and interface requirements. The standard configuration is a 1-pole rotary transformer (Resolver) with an accuracy of approximately ± 10 arcminutes. Optional 3-pole or 5-pole rotation with higher accuracy, reaching ± 5 arcminutes and ± 5 arcminutes respectively. For applications that require absolute value positions, multi turn absolute value encoders such as EON 1325 SSI (G3), ECN 1313 SSI (G5), SRS 50 (G6.1S1), SRM 50 (G6.1M1), SKS 36 (G6.2S1), SKM 36 (G6.2M1), ECN 1313 Endat 2.1 (G12.1S1), ECN 1325 Endat 2.1 (G12.1M1), ECN 1113 Endat 2.1 (G12.2S1), and EON 1125 Endat 2.1 can be selected. (G12.2M1) and others.

The system accuracy of different encoders varies significantly. The end-to-end absolute accuracy of the Resolver is about ± 10 arcminutes, while the G3/G5 encoder can achieve ± 20 arcminutes, and the G12 series is even better. It should be noted that some encoders (such as G6.2, G12.2) are not suitable for CDE3000 and CDF3000 drivers, and driver compatibility must be checked when selecting. Encoder cables must use shielded cables, with both ends of the shielding layer grounded. Differential signals A, B, R or CLK, DATA must be twisted in pairs. If using both rotary and TTL/SSI encoders, an independent 5V power supply needs to be provided for the encoder, and the maximum current should be 150 mA.

The encoder interface is the biggest compatibility challenge when replacing old motors. If the original system uses a Resolver, the new motor should also choose a Resolver, or confirm that the driver supports other encoder types and reconfigure it. If the original system uses an absolute value encoder, the same protocol (SSI or Endat) and resolution must be selected, otherwise the driver cannot read the position correctly. The plug type and pin definition of the encoder cable must also match, and it is recommended to use LT original cables or confirm the pin compatibility of third-party cables.

Maintain and upkeep the brake system

The LSH and LST series can be optionally equipped with a 24 VDC holding brake, model code B. This brake is a backless permanent magnet single-sided brake that uses the principle of locked rotor current, which requires power to release. The brake is directly installed behind the flange (A side) to provide optimal holding torque. Brakes usually switch when stationary, and if used as emergency stop brakes, attention must be paid to the maximum allowable frictional energy WR.

Taking LST-127 as an example, the brake release current is 1.0 A at 20 ° C, the holding torque is 18.0 Nm, the maximum friction energy is 1.29 × 10 ⁶ Ws, the moment of inertia is 0.000166 kgm ², and the mass is 0.9 kg. The release current of LST-158 is 1.1 A, the holding torque is 36.0 Nm, and the friction energy is 2.90 × 10 ⁶ Ws. The release current of LST-190 is 1.1 A, the holding torque is 36 Nm, and the friction energy is 2.9 × 10 ⁶ Ws. The release current of LST-220 is 2.1 A, the holding torque is 145 Nm, and the friction energy is 13 × 10 ⁶ Ws.

The response time of the brake includes the suction time t1 and the release time t2. Taking LST-127 as an example, t1 is 10 ms and t2 is 50 ms. LST-158 has t1 of 22 ms and t2 of 90 ms. The DC side switch (switching between rectifier and coil) can achieve very short overtravel, and for situations that require precise braking, especially for lifting mechanisms, a DC side switch must be used. During brake maintenance, the air gap and friction plate wear should be checked regularly. If the brake does not release, first check if the 24V power supply is normal and if the release current has reached the rated value. If the brake noise is high or the braking torque decreases, it may be necessary to replace the friction pads or the entire brake.

Mechanical installation and axial/radial forces

The installation forms of LT synchronous motors include B5 (flange installation, entering from the housing side), V1 (flange installation, bottom shaft end facing downwards), and V3 (flange installation, top shaft end facing upwards). B5 is the free shaft end, V1 is the bottom free shaft end, and V3 is the top free shaft end. When installed vertically (V1), the allowable axial force FAm applies. When installing (V3) vertically upwards, the allowable axial force needs to be subtracted from the rotor weight FG.

The allowable radial force FRm and axial force FAm depend on the machine frame size, speed, and application point. Taking LST-127 as an example, at 3000 rpm, the radial force FRm is 590 N and the axial force FAm is 110 N. LST-158 has a radial force of 620 N and an axial force of 120 N at 3000 rpm. LST-190 has a radial force of 1170 N and an axial force of 225 N at 3000 rpm. LST-220 has a radial force of 1490 N and an axial force of 280 N at 3000 rpm. These values are based on a lifespan of 20000 hours and are applied at the midpoint of the shaft end. If the point of force application is not at the midpoint, it can be converted according to the leverage ratio. Attention: Radial and axial forces cannot be applied to the motor shaft simultaneously, only one of them can be applied.

During installation, ensure that the motor flange is tightly attached to the installation surface, and tighten the bolts with torque. For shafts with keyway (option P), a suitable coupling or pulley must be used to avoid excessive impact on the keyway. If there are feather keys on the motor shaft end, they must be fixed before debugging to prevent them from flying out during high-speed rotation. Motor cables must use shielded cables, with both ends of the shielding layer grounded, and the cable length not exceeding the maximum allowable value of the driver.

Practical steps for replacing discontinued motors

When the original LT synchronous motor is shut down or damaged and needs to be replaced, it is recommended to follow the following steps:

Record the original motor nameplate data: model, serial number, rated torque, rated speed, rated current, DC bus voltage, encoder type, brake voltage and torque, flange size, shaft diameter, shaft length, installation form.

Search for new models with the same machine base number and length in the LT selection sample. If the original motor is an old model, it may have been upgraded, but the installation dimensions and electrical parameters should be matched as much as possible.

Check the encoder interface: If the original system uses a Resolver, the new motor should also choose a Resolver; If the original system uses an absolute value encoder, confirm that the protocol and resolution are consistent.

Check the brake: If the original motor is equipped with a brake, the new motor must also be equipped with a brake, and the release voltage and holding torque must meet the requirements.

Verify DC bus voltage: 320V and 560V cannot be mixed unless the driver supports a wide voltage range and is reset.

Check the mechanical interface: the flange joint, bolt hole spacing, shaft diameter, shaft length, and keyway size must match. If a perfect match is not possible, consider customizing the design (option X).

After replacement, recalibrate the driver parameters, including motor data, encoder data, current loop, speed loop, and position loop. Suggest using LT's DRIVE MANAGER software to load the corresponding motor database.

Test run: Run at low speed first to check the encoder direction, brake release, motor temperature, vibration, and noise. Then gradually increase the speed and load, and observe whether the current and torque are normal.

Common faults and troubleshooting

Motor overheating: Check if the load exceeds the continuous torque, if the cooling conditions are good, and if the ambient temperature is too high. If the surface temperature of the motor exceeds the allowable value, the load should be reduced or ventilation should be improved. Check if the motor PTC or KTY is correctly connected to the driver and if the temperature protection parameters are set correctly.

Encoder alarm: Check if the encoder cable is securely connected, if the shielding layer is grounded, and if the cable is damaged. If using a Parser, check if the rotation signal is normal; If using an absolute value encoder, check the battery voltage (multiple cycles) and protocol configuration. When the encoder direction is incorrect, A and B can be exchanged or the driver parameters can be adjusted.

Brake not released: Check if the 24V power supply is normal and if the release current has reached the rated value. Check if the rectifier is working and if the DC side switch is functioning properly. If there is noise from the brake, it may be due to worn friction plates or improper air clearance.

Motor vibration or noise: Check the alignment of the coupling, whether the bearings are damaged, and whether the encoder is loose. Check if the current loop parameters of the driver are appropriate and if the carrier frequency is too high.

Excessive axial force causing bearing damage: Check the installation form and whether the axial force exceeds the allowable value when installed vertically. If using pulleys or gears, ensure that the radial force application point does not exceed the allowable value.