REXRTOH MDD Digital AC Servo Motors

Deep Analysis and Application Guide of Rexroth Indramat MDD Digital AC Servo Motor Technology

In the field of modern industrial automation, servo motors serve as the core power source for precise motion control, and their performance directly determines the machining accuracy and dynamic response speed of machine tools, packaging machinery, printing, and robot systems. The MDD (Mannesmann Rexroth Indramat) series digital AC servo motors have become the preferred choice for cost-effective automation systems due to their excellent power density and synchronization characteristics. This article will delve into the technical parameters of the MDD series, covering models from compact MDD 021 to high dynamic MDD 115. Combining engineering practice, it will explore their mechanical design, electrical connections, thermal management, and environmental adaptability, providing engineers with a detailed selection and application guide.

Introduction: Modular Design for Industrial Drive Solutions

The MDD series is an intelligent digital AC servo motor series launched by Mannesmann Rexroth, aimed at achieving cost-effective and fast response automation systems through modular design. This series includes nine motor models with different torques and speeds, which can meet various needs from simple feed axis motion to extreme dynamic applications. When used in conjunction with Indramat intelligent digital drive controllers, MDD servo motors can create an automated solution that is both economical and has high-speed response characteristics.

Core technology architecture and high-performance features

2.1 Permanent magnet technology: low inertia and high dynamics

The rotor of MDD servo motor is made of rare earth or ferrite magnetic materials. This material gives the motor rotor an extremely low moment of inertia. Low inertia is a key indicator of the dynamic performance of servo systems. A lower rotor inertia means that the motor can accelerate and decelerate faster, which is crucial for applications such as packaging printing and CNC machine tools that require extremely high acceleration and dynamic performance.

2.2 Brushless design and maintenance free

Brushless design: Traditional brushed DC motors require regular maintenance due to carbon brush wear, which not only increases downtime but also generates dust.

Maintenance free: The MDD series adopts a brushless design, completely eliminating the maintenance needs caused by carbon brush wear, greatly improving the reliability of the system, and suitable for long-term continuous operation without frequent maintenance.

2.3 High overload capacity and heat conduction

Wide speed regulation range: The motor can maintain high torque within a wide speed range, which is particularly important for packaging machine spindle applications that require constant torque and wide speed regulation. *Efficient heat conduction: The heat generated by the stator winding can be efficiently conducted to the motor housing and cooling air duct, which gives the motor excellent overload capacity.

Series Overview and Application Fields

The MDD series is divided into nine main model series based on torque and speed range. Each model has been optimized for specific loads and applications:

Compact (MDD 021): Designed specifically for screw drives, auxiliary shafts, and tool changers. Suitable for packaging, printing, and auxiliary applications.

High dynamic type (MDD 065, 071, 093): Due to its extremely high power density and overload capacity, it is suitable for high dynamic applications such as roller feed, stamping, punching, and tool changing devices.

High precision type (MDD 090, 112, 115): used for applications that require extremely high synchronicity, such as grinding machines.

Powerful type (MDD 112, 115): As a spindle or tool replacement device, suitable for spindle drives with high torque requirements.

Electrical Connection and Feedback System

4.1 Power Supply and Braking Control

MDD servo motors support integrated electrical connections, simplifying system wiring. The motor power cable integrates power connection, brake control, and temperature monitoring functions. This avoids the complexity of on-site wiring and ensures the reliability of the connection.

Temperature monitoring: The built-in temperature sensor continuously monitors the temperature of the stator winding to prevent overheating damage and improve the lifespan of the motor.

Brake control: Supports external brake connection for static holding of the shaft. The brake holds when the power is off and releases when the power is on. Intelligent digital drivers automatically manage opening and closing timing.

4.2 Feedback device and encoder system

The MDD series supports high-performance motor feedback systems, including parsers and digital servo feedback. This allows users to choose the most suitable technical solution based on their accuracy requirements.

Parser Feedback (RSF): Suitable for harsh environments, sturdy and durable, providing relative position detection.

Digital Servo Feedback (DSF): A high-resolution optical system that provides absolute position detection and is suitable for precise positioning.

Mechanical design, installation, and thermal management

5.1 Installation direction and load bearing capacity

Standard flange installation: All motors support IM B5 flange installation (through-hole).

Threaded flange (IM B14): Some models support IM B14 flange installation (with threaded holes).

Shaft seal: For applications that require dust and water resistance (IP 65), an option with shaft seal is available.

5.2 Bearing Capacity Calculation and Life

Engineers must correctly calculate the radial and axial forces borne by the shaft to avoid shortening the bearing life.

Radial force F_radial: The radial force depends on the average velocity and the distance from the point of action. The document provides detailed calculation charts. For high loads, the bearing life will sharply decrease in a cubic relationship.

Axial force: Axial force is usually less than radial force. The axial force calculation formula is Faxian=0.34 * Fradial (where Fradial is the allowable radial force). Excessive axial force can cause damage to the B-side bearing.

5.3 Surface Cooling and Options

For extreme load conditions, natural cooling may not be sufficient for heat dissipation. Larger models in the MDD series (such as MDD 065 and above) support surface cooling options (fans). *Axial cooling: suitable for scenarios that require a compact structure.

Radial cooling: suitable for scenarios that require short structures.

Cooling system and option expansion

In order to cope with high-frequency start stop and high load, the MDD series provides modular cooling solutions.

Fan model: Provides 1xAC 230V and AC 115V power supply, operates independently.

Options: Includes thermal protection switch and installation components to ensure safety.

Selection and Order Information

Selection is a crucial step in system integration. The correct selection code determines the function, interface type, and accessories of the motor.

7.1 Analysis of Model Code Structure

The model codes of the MDD series strictly follow specific logic.

Structure: For example, in MDD 090 B-N-020, 90 represents the serial number (90), 020 represents the length code, and B represents the standard design.

Feedback options: G represents parser feedback, K represents integrated pulse absolute encoder.

Braking options: 0 represents no braking, 1 represents braking.

7.2 Dimensional Data and Interface Configuration

The technical documentation contains detailed data for all models and is the final step in mechanical integration.