Bonfiglioli BMD Servo Motor Selection and Configuration Guide

Bonfiglioli BMD Series Permanent Magnet Synchronous Servo Motor: Selection and Feedback System Configuration Guide

In the field of modern industrial automation, the performance bottleneck of servo systems often lies not in the controller, but in the matching degree between the motor and the feedback system at the execution end. Bonfiglioli's BMD Series permanent magnet AC synchronous servo motor, with its high neodymium magnet (NdFeB) rotor and compact mechanical design, provides a high dynamic response drive core for industries such as woodworking, metalworking, packaging, robotics, and food and beverage. However, to truly unleash the performance potential of BMD motors, engineers must make precise decisions in the selection, feedback configuration, and wiring stages. This article will provide you with a complete guide from theoretical calculations to engineering implementation based on the core technical parameters of the BMD series.

Understand the core advantages of the BMD platform

It is crucial to understand the design philosophy of the BMD platform before delving into the selection process. This series covers six machine base sizes from BMD 65 to BMD 170, providing a range of locked rotor torque from 0.85 Nm to 45 Nm (naturally cooled) and up to 60 Nm (forced air cooled).

Its core advantages lie in extremely low rotor inertia and high overload capacity. Thanks to the neodymium magnet material, BMD motors can withstand instantaneous peak torque (usually three times the locked rotor torque) without the risk of demagnetization. This characteristic makes it particularly suitable for cyclic operating conditions that require frequent start stop and rapid acceleration/deceleration (Duty type S3).

In addition, the protection level of BMD motors comes standard with IP65 and can be optionally IP67. Coupled with an F-class insulation system, it has strong survivability in harsh environments such as dust and humidity.

Engineering calculation steps for servo motor selection

The correct selection begins with precise calculations. According to the guidelines on page 11 of the manual, selection should take into account both thermal equivalent torque and speed limitations.

1. Equivalent torque calculation（MEQU）

In actual working conditions, the motor does not operate at constant torque. The first step in selection is to calculate the equivalent torque within one working cycle, ensuring that the value is lower than the rated torque of the motor（Mn）. The calculation formula is as follows:

MEQU=M one two⋅tone+

M two two⋅t two+⋯+Mn two⋅tn t one+t two+⋯+tn

Torque at each stage ti

Duration of each stage

The core logic of this calculation is to convert a non constant load into an equivalent constant load for verifying the thermal capacity of the motor. If the equivalent torque exceeds the rated torque of motor S1 under the working system, larger motor specifications or the addition of forced ventilation option (IC416) need to be considered.

2. Temperature correction and speed boundary

Pages 8-9 of the manual define the concept of thermal equilibrium: a state where the rate of temperature change is less than 1K/half hour. Attention should be paid when selecting:

Environmental temperature correction coefficient（ft）When the ambient temperature exceeds the standard operating condition of 40 ℃, the continuous output torque of the motor needs to be reduced according to the curve on page 11 of the manual.

Voltage limit curve: The continuous working area (S1) of the motor is enclosed by the "maximum continuous torque curve" and the "voltage limit curve". The voltage limit is determined by the rated speed of the motor（nn）Decided. The manual clearly states on page 40 that the voltage limit is usually much lower than the mechanical limit speed. When selecting, the voltage limit curve should be chosen to cover the motor with the highest application speed, in order to avoid the driver entering the weak magnetic zone and causing a decrease in efficiency.

Deep analysis and selection of feedback system

A major highlight of the BMD series is the provision of a wide range of feedback options, from highly robust rotary transformers (Resolvers) to high-precision encoders that support Functional Safety. The manual provides detailed explanations on pages 13-15 and 48-51.

1. Parser: A classic choice for high reliability

Model: RES1 (8kHz) and RES2 (10kHz)

Applicable scenarios: environments with high vibration, high temperature, and severe oil pollution (such as injection molding machines and metal cutting machines).

Key parameters: Extreme logarithm of 2, accuracy error of ± 10 '. Its output is an analog sine cosine signal, and the resolution depends on the analog-to-digital converter (ADC) of the driver. The technical parameter table on page 49 of the manual shows that its operating temperature can reach -55 ℃ to+155 ℃, far exceeding that of optical encoders.

2. Optical Absolute Encoders

The BMD series is compatible with high-end optical encoders from Heidenhain and SICK:

Heidenhain ECN/EQN series (ENB1/ENB2): Supports EnDat 2.2 protocol, providing up to 13 bit/turn single turn resolution and 12 bit multi turn counting. Machine tool pivot axis suitable for high-precision positioning.

SICK SKS/SKM series (ENB3/ENB4): Supports Hiperface protocol, with a maximum single loop resolution of 15 bits.

Engineering tip: When choosing an optical encoder, it is important to pay attention to its anti vibration ability. For example, the comparison on page 50 of the manual shows that Heidenhain ENB1/ENB2 has a vibration resistance of 200 m/s ², while SICK ENB3/ENB4 has a resistance of 50g (approximately 490 m/s ²). If applied in situations with extremely high impact loads, priority should be given to selecting models with higher impact resistance specifications.

3. New Inductive and Capacitive Encoders

In response to the pursuit of compact space and high robustness, BMD has introduced bearingless encoder technology:

Heidenhain EQN1131 (ENB8): Based on the principle of inductive measurement, supports EnDat 2.2 protocol, and has functional safety features. Its rotor inertia is only 0.30x10 ⁻⁶ kgm ², which has minimal impact on the dynamic response of the motor.

SICK EEM series (ENB9/ENB12): based on capacitive measurement principle, supporting Hiperface DSL protocol. The ENB12 model also supports functional safety (SIL level).

Selection suggestion: For applications that require SIL (Safety Integrity Level) certification for Safety Torque Off (STO) or Safety Stop 1 (SS1) functions, it is recommended to prioritize ENB8 (EnDat 2.2), ENB10/ENB11/ENB12 (Hiperface DSL), and connect the drive system through the EMA-SABS-21 or EMA-SABS-11 safety modules recommended by Bonfiglioli.

Braking, inertia matching, and forced air cooling options

1. Holding Brake - F24 option

The brake of BMD motor is of power-off braking type, with a power supply voltage of 24V DC. The detailed braking parameters are listed on page 52 of the manual.

Key data: For BMD 170, the braking torque is as high as 36 Nm, but the response time (Engage time+Release time) is approximately 11ms.

Engineering red line: The manual clearly states that this brake is only used for holding braking and is strictly prohibited from being used for dynamic braking, except in emergency situations such as main power failure.

2. Additional Inertia (F1 option)

In high load inertia matching scenarios, a motor body with too little inertia may cause system response oscillations. The F1 option solves this problem by increasing the flywheel mass. According to page 53 of the manual, after adding a flywheel to BMD 145, the inertia increases by 36x10 ⁻⁴ kgm ² and the mass increases by 5.0kg. This can bring the inertia ratio of the motor to the load into a more controllable range (usually recommended 1:5 to 1:10).

3. Forced Ventilation (options such as V1R/V1S)

Only available for BMD 145 and BMD 170. When natural cooling cannot meet the continuous high torque output of S1, forced air cooling (IC416) can increase the locked rotor torque to 60 Nm (page 17 of the manual). It is worth noting that page 54 of the manual provides the ordering code for the retrofit kit (such as 19MOT0013), which allows users to upgrade the standard motor to forced air cooling on site, but requires additional machining of 8 threaded holes on the casing.

Engineering Wiring Practice: Servocables and Connector Layout

The proportion of wiring errors in servo system failures is extremely high. The BMD manual provides extremely detailed pin definitions and cable selection tables on pages 56-67.

1. Principle of Separation of Power and Signal

Power Cable: Orange sheath, compliant with DESINA standards. For motors with feedback, use 6-core (U/V/W+ground+brake+/-) connectors; For the Sensorless version, an 8-pin connector is used (page 56 of the manual).

Signal Cable: Green sheath. Page 63 of the manual provides a detailed distinction between the plug definitions of Resolver (12 pin) and EnDat (17 pin). For example, the Sin+/Sin - of the Resolver corresponds to pins 2 and 1, while the Data+/Data - of EnDat corresponds to pins 14 and 17.

2. The rise of hybrid cables

For motors using Hiperface DSL (ENB9... ENB12) and EnDat 2.2 (ENB8), hybrid connection is supported, where the power line and encoder signal line are integrated into the same cable.

The mixed plug layout of BMD 170 is shown on page 59 of the manual, which has the advantage of significantly reducing the number of interfaces at the motor end, which is crucial for compact installation space with IP67 protection level. When choosing a hybrid cable (such as OCM XX CD1/CO2), it should be noted that its D-SUB pin definition is specifically designed for Bonfiglioli's EM-SABS-11/21 interface module and is not compatible with general third-party drivers. This must be strictly checked during system integration.

3. Bending life of cables

On page 61 of the manual, it is stated that standard servo cables are suitable for dynamic laying, with a bending frequency of no less than 10 times and a maximum acceleration of 15 m/s ². In robot or high-speed truss applications, it is necessary to calculate the bending radius of the cable (>10 times the outer diameter of the cable) and the speed of the drag chain, otherwise the shielding layer will break and the encoder signal will be lost.

Thermal protection and nameplate interpretation

Temperature sensor: BMD motor comes standard with PTC thermistor (KTY or PT1000 optional). On page 52 of the manual, it is clearly stated that the PTC switch temperature matches the F-class insulation (usually 155 ℃). The KTY sensor provides a linear resistance change from 0 ℃ to 170 ℃, which is suitable for situations that require real-time temperature monitoring rather than just switch protection.

Nameplate Analysis: On page 10 of the manual, the nameplate fields are demonstrated through examples, with a focus on the locked rotor torque（M0）Rated torque（Mn）Blocked rotor current（I0）And the back electromotive force constant（Ke）. When debugging servo drives,Ke Value is a key input parameter for calculating weak magnetic points and estimating the angle of the motor magnetic field.

Common selection misconceptions and pitfalls avoidance guide

Neglecting the difference between "stall torque" and "rated torque":

When operating at medium to high speeds (such as above 3000 rpm), the rated torque increases due to iron loss and mechanical friction（Mn）It will be significantly lower than the stalling torque（M0）. The data on page 24 of the manual for BMD 65 0.85Nm shows that its locked rotor torque is 0.85Nm, but at 6000rpm, the rated torque drops to 0.73Nm. If the locked rotor torque is selected, it will cause the motor to overheat at high speeds.

Parser matching failed:

The input voltage and frequency of the Resolver are listed on page 49 of the manual (e.g. RES1 is 7Vrms/10kHz). If the excitation voltage or frequency of the selected third-party driver does not match (for example, some domestic drivers only support 5V/5kHz), the accuracy of the solver will significantly decrease, and it may even fail to work properly.

Insufficient axial/radial load verification:

The maximum radial load provided on page 22 of the manual（FR）The curve is calculated based on a bearing life of 20000 hours. For example, when BMD 118 outputs 6000rpm, the allowable radial force is only about 115N. If synchronous belt transmission is used and the belt tension calculation is too large, it will directly lead to premature fatigue failure of the bearing.