MPM Servo Motors

MPM Servo Motors Selection Guide

MPM Servo Motors Overview

The Kinetix MP-Series Medium Inertia (Bulletin MPM) are compact, power-dense, medium-inertia servo motors from Rockwell Automation. These servo motors leverage the well-proven Kinetix MPL-smart motor technology and high-quality standards to provide a feature-rich motion control solution for applications with heavy payloads and high inertia. Some of the typical applications of the Kinetix MPM servo motors include:

• Printing
• Automotive
• Web Handling
• Material converting

In addition, the Kinetix MP-Series Medium Inertia servo motors offer an extensive range of continuous stall torque of 2.18 Nm to 62.8 Nm (19.3 to 556 lb. in) and peak stall torque of 6.60 Nm to 154.2 Nm (58.0 to 1365 lb. in). They are available in power ratings of 0.75 kW to 7.5 kW (motor-rated power output) and in two classes of armature voltage: 460V AC and 230V AC windings.

The MPM servo motors also provide standard IEC metric dimensions for mounting and rotatable SpeedTEC DIN connectors with flexible connector orientations for easier cable routing. Moreover, their windings are optimized for multiple speed options with compatible Allen-Bradley Kinetix servo drives.

Note: The Kinetix MPM-Series servo motors are broadly classified into two input voltage classes: 200V AC Class and 400V AC Class.

Selecting the Right Kinetix MPM Servo Motor

Generally, a servo motor is usually a part of a servo system that provides motion to a connected load – to lift it, move it, machine it, inspect it, etc. Essentially, the servo motor functions as the muscle of the servomechanism, as it provides the torque and velocity (necessary load point) required to perform a given function, e.g., to move and accelerate the connected load as commanded by a servo controller or as per the applied voltage and current.

Therefore, it is necessary to select a servo motor that can reliably meet the requirements of your servo system.  To do so, you should consider several factors when selecting the servo motor, including the required load torque or force, motion profile, speed, available physical envelope, and specified environmental ratings. This means that the selected servo motor must provide the required load torque and speed, fit in the available installation space, and perform reliably under the subjected environmental conditions of your application.

In that regard, here are the various factors you should evaluate when selecting an Allen-Bradley Kinetix MPM servo motor for a specific application.

1) Load Inertia

Correctly sizing and selecting a Kinetix MPM servo motor starts with knowing the amount of load to be moved, which is described in terms of inertia. Specifically, the inertia ratio is crucial when sizing an MPM servo motor. Inertia ratio is defined as the ratio of the load inertia to the motor inertia, calculated by the following formula: Inertia Ratio = JL/JM; where,

• JL = Moment of inertia of the total load, as reflected to the servo motor
• JM = Moment of inertia of the servo motor

You can find the moment of inertia of the Kinetix MPM servo motors from the data sheets provided by Rockwell Automation. However, calculating the load’s moment of inertia can be a bit complicated because each component in the servo system that’s to be moved by the MPM servo motor contributes to the total load inertia (JL). This includes the connected load and other mechanical components of the servo system’s transmission, such as lead screws, couplings, rails, etc.

2) Speed Requirements

Knowing the motion profile and inertia ratio of the servo system in which the MPM servo motor will be used helps to determine the motor's required speed, torque, and acceleration. For applications involving non-repetitive tasks such as milling, you should determine the maximum velocity necessary (speed), and acceleration and select an MPM servo motor whose speed rating can meet the speed requirements of such loads. 

For servo systems required to perform repetitive tasks, you should plot the necessary servo motor speeds and allow for acceleration and deceleration time since standard MPM servo motors cannot change their speed in steps. The Kinetix MPM-Series servo motors provide base speeds of 1250 to 6000 RPM, rated speeds ranging from 1750 to 5000 RPM, and maximum speeds varying from 2000 to 7000 RPM.

3) Torque Requirements

Depending on your motion control application, there are different speed and torque requirements that the selected Kinetix MPM servo motor will need to meet. While the capability of a servo motor is described by its speed-torque curve, the requirements of an application are best illustrated using its torque and speed profiles, which are additional critical elements in selecting the suitable MPM servo motor.

Once the load inertia and speed requirements are determined, the next step is calculating the required torque values. This can be established from the provided torque-speed curves of the MPM servo motors. The torque calculations should be made to determine the required peak torque, continuous torque, and maximum motor speed. The amount of continuous torque required of the MPM servo motor should be within the continuous operating region of the servo motor’s torque-speed curve. At the same time, the amount of peak torque required of the MPM servo motor should be within the intermittent operating region of the servo motor’s torque-speed curve.

• Continuous Torque: Also referred to as the RMS (Root Mean Square) torque, the continuous torque indicates the torque the servo motor can generate during a complete load cycle. Its value should be within the continuous region of the motor’s torque-speed curve to maintain the required speed.
• Peak Torque: This is the maximum torque required at any point throughout the load cycle. Ideally, the peak torque value should be within the intermittent region of the servo motor’s torque-speed curve since it is not sustainable. If the required peak torque is in the continuous region of the motor’s torque-speed curve, then the servo motor is most likely oversized.

Note: The servo motor speed-torque curves supplied by Rockwell Automation are essential when sizing and selecting MPM servo motors. For example, to prevent your servo motor from overheating during use, select an MPM servo motor that includes all the specific capabilities required for your application.

The provided speed-torque curves also ensure that the required speeds and torques of the application, whether intermittent (peak) or continuous, can be achieved with the Kinetix MPM servo motor you select. So, after examining your application's speed and torque profiles and computing the RMS torque, check the speed-torque curves of specific Kinetix MPM servo motors and see if they’ll fit your application.

4) Frame Size

The Kinetix MPM servo motors are currently available in four frame sizes – 215 mm, 165 mm, 130 mm, and 115 mm. These frame sizes feature 1 to 4 high-energy, rare-earth magnetic stack lengths.

Generally, the physical size of a servo motor is often determined by its continuous torque-producing capacity with a tradeoff between motor length and motor diameter. For example, a Kinetix MPM-Series servo motor with a small diameter and longer length can have the same torque rating as a larger diameter, shorter length Kinetix MPM servo motor. Also, you can achieve the power requirements of your servo system by using a smaller Kinetix MPM servo motor and multiplying its output torque through a gearbox or applying alternative technologies, such as direct-drive motor technology, frameless/kit, or linear servo motors. Each of the aforementioned servo motor technologies is available with varying motor frame sizes that can address specific space requirements.

5) Type of Feedback Element

In most servo systems, the feedback device is often integrated into the servo motor, but it can also be used as a standalone unit installed a distance from the motor. Its role is to analyze the correlation between the control input signal given by the system’s servo controller and the real-time position of the servo motor. It then generates an appropriate feedback signal from the evaluation, which it sends to the connected servo drive and/or to the system’s servo controller through its control loop. The feedback element can be an encoder, a Hall Effect sensor, a potentiometer, a resolver, a linear transducer, or an advanced vision system.

To select the best feedback element for your servo system, ensure that you understand the system’s resolution requirement, as well as the speed, position, and torque control requirements of your motion control application.

The Kinetix MPM-Series is available with a choice of Multi-turn (-M) or Single-turn (-S) high-resolution, high-performance encoders. Hence, depending on your system’s resolution and motion control requirements, select a Kinetix MPM servo motor that incorporates any of the following encoders:

• A Single-turn, high-resolution encoder providing absolute position feedback in one turn.
• A Multi-turn, high-resolution encoder providing absolute position feedback in 4096 turns. This encoder does not require a backup battery.
• Multi-turn and Single-turn encoders with 1024 sin/cos cycles per revolution for a maximum of 2,097, 152 CPR (counts per revolution) or 21-bit resolution. Rockwell Automation supplies these encoders with the following Kinetix MPM servo motors: MPM-A/B215x, MPM-A/B165x, MPM-A/B130x, MPM-A/B115x servo motors.

6) Compatible Kinetix Servo Drives

As previously stated, servo motors are often part of a closed-loop servomechanism system that includes a servo drive, feedback element, and servo controller. The servo drive functions as the brain of the servomechanism system; it receives a command input signal from the system’s controller and amplifies it to provide an absolute amount of input voltage and current to the connected servo motor, enabling the motor to accomplish the required motion.

The servo drive can also adjust the operating variables of the servo motor in real time based on the error value between the reference command signal and the system’s feedback signal. This ensures that the servo motor is functioning as commanded. Therefore, when selecting a  Kinetix  MPM servo motor, ensure that you also check its compatible Kinetix servo drives for effective servo system performance.

The Kinetix MP-Series (Bulletin MPM) Medium-Inertia servo motors are compatible with these Allen-Bradley Kinetix servo drives:

• Single-axis Kinetix 300 Indexing, EtherNet/IP servo drives
• Single-axis Kinetix 350 EtherNet/IP servo drives
• Multi-axis Kinetix 6500 and Kinetix 6200 modular servo drives
• High-power Kinetix 7000 servo drives
• Low-power, multi-axis Kinetix 2000 servo drives
• Multi-axis Kinetix 5700 EtherNet/IP servo drives
• Multi-axis Kinetix 6000 servo drives
• Kinetix 5500 EtherNet/IP servo drives. To use these servo drives with the Kinetix MPM servo motors–200V-Class, the Hiperface-to-DSL feedback conversion kit (Catalog No. 2198-H2DCK, series B or higher) is required.

7) Available Motor Options

The Kinetix MPM-Series servo motors are available with various optional features, including:

• A 24-Volt DC holding brake, which also functions as an occasional stopping brake
• Nitrile-based shaft seals and replacement kits used for field modifications/installations. The kits also incorporate a lubricant to minimize wear in the servo system. The shaft seals should be inspected and replaced regularly as they’re subject to wear. It’s recommended that you replace them after every three months.
• A positive air-pressure kit (Cat. No. MPF-7-AIR-PURGE). This kit is usually mounted on the MPM servo motor’s feedback connector plug to provide additional positive air pressure, which helps to further lessen the possibility of contamination in the servo motor.

Check if the Kinetix MPM servo motor you intend to select is available with the aforementioned optional features, as they provide added functionality for motion control applications with heavier payloads and greater inertia.

8) Compatible Connectors and Cables

Be sure to select a Kinetix MPM servo motor that’s equipped with compatible SpeedTEC DIN connectors. Also, ensure that the necessary cables and plugs to be used with the MPM servo motor you’re planning to purchase are provided.  

Overall, the Kinetix MPM-A/Bxxx motors are compatible with the 2090-CxxM7xx servo cables and with the M4 and M7 SpeedTEC DIN cable plugs. The M4 cable plugs require an O-ring, while the M7 cable plugs should be attached with one-quarter turn.

9) Environmental Specifications

Environmental factors, such as ambient temperature, humidity, and air pressure, affect the overall selection of Kinetix MPM servo motors because if the conditions of the working environment are different from the environmental ratings of the selected servo motor, then its performance will change. For example, the higher the ambient (surrounding) temperature of a servo motor, the lower the possible continuous torque. Thus, in a working environment where high surrounding temperature and/or continuous torque is required, liquid cooling can be implemented, but direct contact of the coolant and the servo motor’s mechanics and connections should be avoided.

Other environmental factors to consider when selecting an MPM servo motor include presence of contaminants (physical, chemical), tolerable mechanical shock and vibration levels, relative humidity, required enclosure ratings, shaft seals specifications, etc.

In general, the Kinetix MPM-Series servo motors require an operating temperature of 0 to 40 degrees Celsius (32 to 104 degrees Fahrenheit), relative humidity (storage) of 5% to 95%–without condensation, storage temperature ranging between -30 to 70 degrees Celsius (-22 to 158 degrees Fahrenheit), and a non-corrosive storage atmosphere. The specified environmental ratings for the MPM servo motors are:

• IP50 minimum rating (standard), without optional shaft seal
• IP66 rating that provides an optional shaft seal. This rating also requires the use of environmentally sealed motor cables and connectors. 

Note: The selected Kinetix MPM servo motor should be compliant with appropriate CSA and UL standards. It should also be CE-marked and certified for all applicable regulatory directives.

Take Away

Selecting the right Kinetix MPM servo motor starts with understanding your application, establishing the characteristics of the load to be moved, how it will be moved, and how fast. From there, you can determine the speed and torque requirements of the suitable motor, which considerably narrows down the MPM servo motors to choose from. 

To select a specific Kinetix MPM servo motor, you’ll then be required to specify its frame size, type of integrated encoder, compatibility with various Kinetix servo drives, available optional features, compatible cables, and connectors, as well as its environmental rating. Other factors like recommended working environment conditions, efficiency, gearing, and accuracy should also be considered.