Bonfiglioli BTD/BCR Synchronous Servo Motor Selection and Interface Configuration Guide



Bonfiglioli Vectron BTD/BCR synchronous servo motor: professional selection and technical characteristics

In the field of modern industrial automation, the requirements for dynamic response, accuracy, and efficiency of motion control systems are becoming increasingly stringent. Bonfiglioli Vectron's BTD and BCR series permanent magnet synchronous servo motors provide high-performance drive solutions for industries such as packaging, textiles, machine tools, robots, and material handling, thanks to their optimized magnetic circuit design, compact structure, and rich feedback options. This article aims to provide engineers with a detailed technical reference, covering the technical differences between two series, key selection parameters, mechanical interface specifications, and feedback system configurations.

BTD and BCR series: Technical positioning and core differences

The Bonfiglioli Vectron servo motor series covers a wide range of application needs through two different technological paths.

BCR series (Brushless Classic Range): This series adopts standard wound stator technology, emphasizing high dynamic response and large torque range. Its continuous stalling torque covers 0.2 Nm to 115 Nm and has an instantaneous overload capacity of up to 400%. This makes the BCR series very suitable for applications that require frequent start stop, rapid acceleration and deceleration, and the ability to withstand impact loads, such as robot joints, high dynamic packaging lines, and metal cutting machines.

BTD series (Brushless Torque Density): This series adopts advanced winding magnetic pole technology, with core advantages of high torque density (up to 16 Nm/dm ³) and compact volume. Under the same torque output, the installation space of BTD motor is smaller. Its torque density range is approximately 3.4 to 5.6 Nm/dm ³, making it particularly suitable for applications with limited installation space but high torque output requirements, such as precision electronic manufacturing equipment and compact automation units.

Selection decision point: If the main challenge of the application is space limitation, prioritize the BTD series; If the main challenges are extreme overload and dynamic response, the BCR series is a more suitable choice.

Interpretation and selection calculation of key technical parameters

A correct understanding of motor parameters is the foundation for ensuring system performance matching.

1. Stuck torque (M ₀) and rated torque (M ₙ)

Locking torque (M ₀): The maximum torque that the motor can continuously output at zero speed, which is the primary reference value for selection.

Rated torque (M ₙ): The torque that the motor can continuously output at rated speed. Usually M ₙ is slightly smaller than M ₀.

Selection rule: The continuous torque required for the application (including safety factor) should be less than or equal to the rated torque of the motor (M ₙ). For periodic loads, it is necessary to calculate the effective torque (RMS torque) to ensure that it is less than M ₙ.

2. Torque constant (K ₜ) and back electromotive force constant (K ₑ)

Torque constant (K ₜ, Nm/A): represents the torque that the motor can generate per ampere of current. The larger the K ₜ value, the greater the torque generated under the same current.

Reverse electromotive force constant (K ₑ, V/1000 min ⁻¹): represents the reverse voltage generated by the motor every 1000 revolutions. K ₑ determines the driving voltage required by the motor at a specific speed.

Relationship: Under the SI unit system, K ₜ (Nm/A) ≈ K ₑ (V/(rad/s)). But the K ₑ unit in the manual is V/1000min ⁻¹, so when converting, attention should be paid to the unit conversion (1 V/1000min ⁻¹ ≈ 0.00955 V/(rad/s)).

3. Moment of inertia (J ₘ) and mechanical time constant (τₘₑ c)

Moment of inertia (J ₘ, kgcm ²): affects the acceleration capability of the system. The ratio of load inertia to motor inertia (inertia ratio) is a key parameter that determines the response speed and stability of the system. The recommended inertia ratio for high dynamic applications is ≤ 5:1.

Mechanical time constant (τₘₑ c, ms): represents the theoretical time required for the motor to accelerate from zero to rated speed. The smaller the τₘₑ c, the faster the dynamic response of the motor. From the data, it can be seen that due to optimized rotor inertia design, the mechanical time constant of the BTD series is usually smaller than the BCR of the same aircraft number (such as BTD5 being 0.4-0.7ms and BCR5 being 0.7-1.4ms), indicating that BTD has faster acceleration capability.

Mechanical interface and installation specifications

The BTD and BCR series use standardized mechanical interfaces to facilitate coupling with gearboxes or other transmission components.

1. Flanges and shaft extensions

According to the motor size (Size 2 to 8), different flange interfaces (IMB table) have been defined. Taking standard configuration as an example:

BTD2/BCR2: Shaft diameter D=9 mm, shaft length E=21.5 mm, flange stop A=40 mm, installation hole spacing B=63 mm.

BTD4/BCR4: Shaft diameter D=24 mm, shaft length E=46.5 mm, flange stop A=130 mm, installation hole spacing B=165 mm.

BCR8: Shaft diameter D=42 mm, shaft length E=106 mm, flange stop A=230 mm, installation hole spacing B=265 mm.

Attention: The maximum allowable radial and axial forces corresponding to different sizes (see the "Max load on shaft" table in each chapter of the manual) must be checked during selection. Radial force (F_R) usually refers to the pressure generated by pulley or sprocket transmission, while axial force (F_A) refers to the thrust parallel to the motor shaft. Exceeding the allowable value will directly lead to a shortened bearing life or a risk of shaft breakage.

2. Installation and alignment requirements

The installation surface must be flat to ensure a tight fit between the flange and the equipment.

When connecting the coupling, it is necessary to strictly calibrate the coaxiality between the motor shaft and the load shaft to avoid generating additional radial stress. It is recommended to use a highly elastic coupling to absorb slight alignment errors.

Feedback system: parser and encoder options

The accuracy of feedback equipment directly affects the control accuracy and speed stability of the motor.

1. Standard configuration: Transformer (Resolver)

All BTD and BCR motors come standard with 2-pole rotary transformers. The main technical indicators are as follows:

Accuracy: The absolute accuracy can reach ± 4 '(arc minutes), and the repeatability accuracy is 1', which can meet the vast majority of industrial applications.

Environmental adaptability: The rotary transformer is a sturdy and durable magneto resistive sensor that can withstand temperatures ranging from -55 ° C to+155 ° C. It has strong resistance to vibration and pollution, making it very suitable for harsh industrial environments.

Interface: Connected through a 12 core signal connector, the driver interface is usually SUB-D9 or terminal connection (requires EMRES-03 interface module).

2. Optional configuration: Encoder

For applications that require higher accuracy, lower speed fluctuations, or absolute position memory, multiple incremental or absolute encoders can be selected:

SinCos incremental encoders (such as Heidenhain ERN series): provide high-resolution sine and cosine signals, and with the interpolation technology of the driver, can achieve extremely high positioning accuracy.

Absolute encoders (such as Heidenhain ECN/EQN series or Sick Stegmann Hiperface series): transmit absolute position data through EnDat or Hiperface protocols without the need for zeroing operations, suitable for multi axis linkage and complex contour machining.

Selection suggestion: If you need to memorize the position or perform high-precision contour processing after power failure, absolute encoders should be preferred.

Thermal protection and braking options

1. PTC thermistor protection

All motors come standard with PTC thermistors (compliant with DIN 44081) and are integrated into the signal connectors of the motor windings (pins 2 and 6). The driver monitors the changes in PTC resistance value to determine the winding temperature in real time. When the temperature reaches the protection threshold (usually 140 ° C), the driver should immediately cut off the output to protect the motor from overheating and burning out. It is strictly prohibited to operate the motor without PTC monitoring.

2. Maintain the holding brake

As an optional item, the rear of the motor can be integrated with an electromagnetic brake that is spring-loaded and electrically released. Its main purpose is:

When the drive is powered off or emergency stopped, hold the motor shaft tightly to prevent the load from falling due to gravity (such as a vertical axis).

When the motor is stationary for a long time, replacing the output torque of the driver can save energy and prevent the motor from overheating.

Selection precautions:

The brake adopts 24V DC power supply (tolerance+6%/-10%).

Installing the brake will increase the length and total weight of the motor. The specific increment can be found in the size chart (K value variation) of each machine base in the manual.

The brake torque in the data table (such as 2 Nm for BTD2 and 145 Nm for BCR8) is usually much smaller than the motor stalling torque and is only used for static holding and cannot be used for dynamic braking.

Electrical connection and cable selection

1. Power connector

Adopting a 4+4-core heavy-duty connector (compliant with Desina standards), it integrates motor power lines and brake power lines. The pin definitions are unified, and even if no brake is selected, the pin positions are still retained in the connector for easy wiring.

2. Signal connector

Using a 12 core connector for transmitting rotary transformer signals and PTC signals. If an absolute value encoder is selected, it will be replaced with a higher density connector (such as 17 cores) to accommodate the additional data cables required by EnDat or Hiperface protocols.

3. Selection Guide for Servo Cables

The manual provides detailed optional cables (orange power cable, green signal cable) and their models.

Power cable: Four wire diameters of 1.5 mm ², 2.5 mm ², 4.0 mm ², and 10.0 mm ² are provided according to the motor current. For example, a high-power motor with BCR 8 size requires the use of a 10.0 mm ² cable (model 42MBCx100).

Signal cables: divided into resolver cables (8RTCxx25) and EnDat/Hiperface cables (17ETCx01/12HTCxx01) according to feedback types.

Length: The standard offers three specifications: 3 meters, 5 meters, and 10 meters. Signal attenuation and voltage drop should be considered when exceeding 10 meters, and the manufacturer should be consulted.

Selection process and examples

Selection steps:

Define application requirements: Calculate the required continuous torque (M.rms), peak torque (M.peak), and maximum speed (n_max).

Select Series: Pre select BTD (Compact) or BCR (High Overload) series based on installation space and overload requirements.

Preliminary Table Selection: In the performance table of the corresponding series, find the machine base number (size) with locked rotor torque (M ₀) and rated torque (M ₙ) that satisfy M ₙ ≥ M rms and peak torque (M max ≥ M peak).

Verification of inertia: Calculate the ratio of load inertia (JL) to motor inertia (JM) to ensure compliance with dynamic requirements (JL/JM ≤ 5-10 times).

Verify mechanical load: Confirm that the external radial/axial load is less than the allowable value of the motor.

Select feedback and accessories: Select the feedback type (Resolve/Encoder) based on control accuracy requirements, and confirm whether a brake is needed based on vertical axis or shutdown requirements.

Configure order number: Generate a complete order number based on the selected parameters and the commercial code rules in the manual.

Example: A packaging machine needs to drive a cutting blade, with a calculated continuous torque of 4 Nm, peak torque of 12 Nm, and a speed of 2800 min ⁻¹. The installation space is limited. In the BTD series, the torque of BTD4-0410 (M ₀=4.1Nm, M ₙ=3.2Nm) is close to the limit, and the peak value of 11Nm is slightly lower; BTD4-0630 (M ₀=6.3Nm, M ₙ=4.6Nm) can provide sufficient margin. Ultimately, BTD4-0630-30-400 can be used in conjunction with a rotary transformer, and the radial load should be verified to meet the requirement of 648N.