MITSUBISHI MDS-B servo troubleshooting

MITSUBISHI MDS-B Series Servo Drive Maintenance and Troubleshooting Guide

System Overview and Security Upgrade Background

The Mitsubishi MDS-B series servo/spindle drive system is a comprehensive upgraded version of the MDS-A series, with core improvements aimed at meeting European safety standards (LVD) and enhancing system integration. This series consolidates the traditional rectifiers scattered in various servo and spindle drive units into independent power supply units (CV), significantly reducing heat generation and installation volume.

For engineers transitioning from the MDS-A series to the MDS-B series or facing maintenance difficulties with outdated MDS-A equipment, understanding the hardware changes, wiring differences, alarm codes, and parameter compatibility of the MDS-B series is crucial. This article will systematically outline the key points of drive replacement, fault diagnosis, and safety configuration based on the MDS-B series technical specification manual.

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Selection and replacement precautions for power supply unit (MDS-B-CV)

2.1 Capacity Calculation Formula

When using a power unit to drive multiple servo/spindle motors, the capacity must meet the following conditions:

Single servo shaft: power unit capacity>∑ (spindle motor output)+∑ (servo motor output)

Two or more servo axes: power unit capacity>∑ (spindle motor output)+0.7 × ∑ (servo motor output)

Note: Motor output refers to the rated output power (kW) of the motor, not the capacity of the drive unit. The spindle motor shall have a rated output of 30 minutes.

For example, if the spindle motor is 7.5kW and the three servo motors are 2kW, 1kW, and 1kW respectively, the calculated value is 7.5+0.7 × (2+1+1)=10.3kW, and an 11kW power supply unit (MDS-B-CV-110) should be selected.

2.2 Special Requirements for MDS-B-CV-370

MDS-B-CV-370 (37kW) is a newly added high-capacity model that requires the installation of external contactors and cannot share contactors with other power units. Its surge charging sequence is different from other CVs, and sharing a contactor can cause damage. The setting rules for the rotary switch (SW1) are as follows:

When using a contactor: SW1=0 or 3

When not using a contactor: SW1=1 or 5 (CV-370 is prohibited from being set to 1 or 5)

When the external emergency stop function is enabled: SW1=4 (contactor valid) or 5 (contactor invalid)

2.3 Configuration principles for multiple power supply units

When the total power exceeds 38kW, two or more power units need to be used:

The first power unit is responsible for the spindle motor power (≤ 38kW)

The second power unit is responsible for the remaining spindle power plus 0.7 times the total servo power

Key limitation: The AC reactors of each power unit must be independent and cannot be shared. Contactors can be shared in principle, but CV-370 must be independent. When connecting the busbars (L+, L -, L11, L21), they must be wired independently and cannot be short circuited or interconnected.

Main circuit wiring specifications and wire diameter selection

3.1 Power input wire diameter (reference value)

Recommended wire diameter for power unit capacity (IV/IV)

CV-37/CR-37 IV3.5SQ or HIV2SQ

CV-55/CR-55 IV5.5SQ or HIV3.5SQ

CV-75 / CR-75 HIV5.5SQ

CV-110 IV14SQ or HIV8SQ

CV-150 IV22SQ or HIV14SQ

CV-185 IV30SQ or HIV22SQ

CV-220~260 IV38SQ or HIV30SQ

CV-300~370 IV60SQ or HIV38SQ

3.2 L+, L-Bus Wire Diameter (Unified Method)

To simplify spare parts, the bus wire diameter can be uniformly selected according to the capacity of the power unit:

CV capacity wire diameter

≤37kW IV3.5SQ / HIV2SQ

55~75kW IV5.5SQ / HIV3.5SQ

110~150kW IV14SQ / HIV8SQ

185~220kW IV22SQ / HIV14SQ

260~300kW IV38SQ / HIV22SQ

370kW IV60SQ / HIV50SQ

3.3 EC Directive Compliance Wiring Points

All terminals must be crimped with insulated tubes to prevent short circuits between adjacent terminals

The protective grounding (PE) terminal must be wired separately and cannot be shared by multiple wires

The power input side needs to be equipped with non fuse circuit breakers and electromagnetic contactors that comply with EN/IEC standards

The U, V, and W output phase sequence of servo/spindle drives must strictly correspond to motor terminals A, B, and C

It is strictly prohibited to install phase capacitors or surge absorbers on the motor output line

Analysis and Handling of Common Alarm Codes

4.1 Power Supply Unit (CV) Alarm

Common Reasons and Countermeasures for Removing the Meaning of Alarm Number LED Display

63 3 Auxiliary regeneration abnormality (transistor continuously conducting) PR (power supply re powering on) Regeneration transistor failure, power supply unit needs to be replaced

65 5 Surge Relay Abnormal PR Surge Resistance Short Circuit Relay Not Closed, Check Contactor and AC Reactor

67 7 missing phase PR input power supply R/S/T, one phase is open circuit, check the power supply line

69 9 grounding fault PR motor or power line short circuit to ground, need to be checked with a megohmmeter

73 J regeneration PR (needs to be controlled for more than 15 minutes to reset). If the regeneration energy exceeds the capacity of the power unit, it is necessary to increase the regeneration resistance or reduce the acceleration and deceleration frequency

75 L overvoltage NR (NC reset) L+and L - voltage exceeds 410V, check the input voltage and regeneration resistor

6B surge relay fused PR relay contact not disconnected, power supply unit needs to be replaced

Special note: After alarm 73 occurs, even if NC is restarted immediately, it cannot be resolved. The control power supply (L11, L21) must be kept powered on for more than 15 minutes to allow internal heat accumulation to dissipate. Frequent alarm 73 may cause a fire due to overheating of the external regenerative resistor. Do not blindly switch on the power repeatedly.

4.2 External emergency stop function (newly added to MDS-B)

The B series has added an external emergency stop input terminal to the CN23 connector, which can achieve dual protection:

Enabling conditions: Set the rotary switch to 4 (contactor valid) or 5 (contactor invalid), and increase the parameter PTYP by 0040 (hexadecimal)

Action logic: If the external emergency stop input lasts for more than 200ms and no NC contactor OFF command is received within 30 seconds, CV will forcibly cut off the contactor itself

Related alarms:

Display "76": External emergency stop setting error (rotation switch does not match PTYP)

Display 'q6F': External emergency stop input is valid but NC does not provide an emergency stop status

Key parameters and debugging of servo drive (MDS-B-V1)

5.1 Special treatment of dynamic brakes

The MDS-B-V1-110/150 (11kW/15kW) drive unit does not have a built-in dynamic brake and must be externally connected to the MDS-B-DBU-150 dynamic brake unit. When wiring, two modes should be distinguished:

Only use dynamic braking: Connect DB1/DB2 of DBU in series to the main circuit DC bus, and connect the control coil to 24VDC

Dynamic braking+electromagnetic braking combination: A dual protection sequence needs to be designed to ensure delayed release of electromagnetic braking after dynamic braking action

5.2 Current Limit Parameters (SV013 ILMT1)

SV013 is set as a percentage of the rated current for motor stalling. If the maximum output torque of the driver is required, set it to 500%. The maximum current reference values for each motor are as follows:

Motor model locked rotor current (A) maximum current (A) maximum torque (N · m)

HA40N 3.6 17 14.2

HA80N 6.6 28 25.5

HA100N 14 42 42

HA200N 22 57 60

HA300N 37 85 87

HA053 1.4 3.9 0.69

Reducing SV013 can limit torque output and is suitable for debugging or light load protection.

5.3 Resolution Setting of Position Detector (SV019/SV020)

Proper settings are required when using different encoders:

Encoder type resolution RNG1 RNG2

OHE25K-6 / OSE104 25000p/rev 100 100

OSE105 / OSA105 1,000,000p/rev 1000 1000

Built in motor (HA053/13) 2500p/rev 10 10

When mixing MP scales, SV019/SV020 should be set according to the actual resolution.

The Use and Sequence Design of Electromagnetic Brakes

6.1 Brake characteristic data

Motor model: Static friction torque release, delayed braking, delayed single allowable braking power

HA053B/13B 0.39 N·m 0.03s 0.10s 5.6 J

HA23NB/33NB 1.96 N·m 0.05s 0.20s 49 J

HA40NB/80NB 5.88 N·m 0.07s 0.24s 294 J

HA100NB~300NB 29.42 N·m 0.10s 0.27s 980 J

6.2 Vertical axis safety sequence

To prevent the vertical axis from slipping due to power failure, the following sequence must be used:

NC issues servo OFF command

The dynamic brake immediately activates (decelerates)

After the motor speed drops below the brake action threshold, cut off the excitation of the electromagnetic brake

The servo main circuit can only be closed after the electromagnetic brake is fully closed (with a delay time of about 0.1~0.27s)

It is strictly prohibited to directly cut off the excitation of the electromagnetic brake in the servo ON state, otherwise it will cause excessive wear of the brake liner.

6.3 Preparation of excitation power supply for brake

The brake requires an external 24VDC power supply, and the current capacity is selected according to the motor model:

HA053B/13B：≥0.5A

HA23NB/33NB：≥0.7A

HA40NB/43NB/80NB/83NB：≥0.9A

HA100NB~900NB：≥1.5A

Unit heat dissipation and installation spacing

7.1 Heat Calculation

The heat generation of each unit (unit: W) is as follows (typical values of B series):

|Power supply unit| CV-37:55 | CV-55:65 | CV-75:80 | CV-110:125 | CV-150:155 | CV-185:195 | CV-220:210 | CV-260:260 | CV-300:320 |

|Spindle drive| SP-04:30 | SP-15:50 | SP-37:80 | SP-75:140 | SP-110:185 | SP-150:240 | SP-185:350 | SP-220:375 | SP-300:635 |

|V1 servo| V1-01:20 | V1-05:35 | V1-20:80 | V1-45:160 | V1-70:245 | V1-90:285 | V1-110:400 | V1-150:550 | — |

When fully enclosed, the heat emitted outside the cabinet is (heat generation constant) × 0.85. A fan for forced convection should be installed inside the cabinet to avoid heat accumulation at the top.

7.2 Installation Space Requirements

The spacing between units should be ≤ 3cm. If it exceeds 3cm, it should be handled according to the requirements of Section 4.3 (busbar length ≤ 50cm, and double line binding)

Servo drive units and spindle drive units above 11kW must be installed adjacent to the power supply unit, with the priority order being: V1-150>V1-110>SP-300>SP-260>

Small power units (9kW and below) can be installed separately, but it is necessary to ensure that the bus voltage drop is acceptable

Common on-site troubleshooting cases

Case 1: Alarm 63 after power on (abnormal auxiliary regeneration)

Phenomenon: MDS-B-CV-110 alarms 63 when powered on and cannot be reset.

troubleshoot

Measure the resistance between L+and L -, which should be in the megaohm range. If it is low resistance, the regenerative transistor will break down

Check if the external regeneration resistor is short circuited or has a low resistance value

Solution: Replace the power unit or regenerative transistor module. Note that the regeneration circuit design of MDS-B-CV-370 is different and cannot be mixed.

Case 2: Restarting after emergency stop displays "6F" and cannot be moved

Phenomenon: After resetting the external emergency stop button, the NC has cleared the emergency stop state, but the driver still displays "q6F" and the axis cannot be enabled.

troubleshoot

Confirm whether the rotary switch SW1 of MDS-B-CV is set to 4 or 5 (enabling external emergency stop function)

Check if parameter PTYP has been added with 0040

Measure whether the 24V on the CN23 connector has been restored

Solution: If the external emergency stop circuit has been closed but still reports an error, it may be due to poor contact of CN23 or incorrect parameter writing. Reset PTYP and power off to restart.

Case 3: The vertical axis slides too far after power failure

Phenomenon: After emergency stop or power outage, the Z-axis slides down beyond the safe distance.

troubleshoot

Check if the delay time of the electromagnetic brake matches the parameters SV055/SV056

Confirm if the dynamic brake is effective (V1-110/150 requires an external DBU)

Solution: Set SV056 to the same value as the acceleration and deceleration time of CNC G0 (usually 40-200ms), and ensure that the brake power supply is delayed and cut off after the servo is turned off.

Maintenance and spare parts recommendations

Electrolytic capacitors: It is recommended to replace the electrolytic capacitors in the power unit and drive unit every 5 years under normal conditions to prevent aging and increase in ripple

Cooling fan: It is recommended to install an auxiliary fan (FAN2) in the distribution cabinet to maintain heat dissipation even if the unit's built-in fan (FAN1) fails

Battery: The battery unit for absolute position detection (MDS-A-BT-2/4/6/8) must be replaced while maintaining control power after the battery low voltage alarm, otherwise the absolute position will be lost

Firmware version: Differences in MDS-A series and B series servo software versions may result in parameter incompatibility. When replacing the drive unit, confirm that the software version is ≥ B0 (for serial pulse encoders)