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Allen-Bradley MPL-B680D-SJ74AA Servo Motor – Detailed Specifications, Product Introduction, Applications, Advantages, and Related Model Guide

1. Product Overview

The Allen-Bradley MPL-B680D-SJ74AA is a large-frame MP-Series MPL low-inertia brushless AC rotary servo motor designed for demanding industrial motion-control applications.

This model belongs to the high-torque section of the MPL servo motor family. It uses a 215 mm frame, an approximately 203.2 mm magnet stack, and a 2000 rpm speed class. Its approximately 62.8 N·m continuous stall torque and 154.2 N·m peak stall torque make it suitable for substantial mechanical loads where a smaller servo motor would not provide enough torque reserve.

The key configuration of the MPL-B680D-SJ74AA is its combination of single-turn high-resolution absolute feedback, keyed shaft, 24 V DC holding brake, and right-angle rotatable SpeedTEC DIN connector.

The integral brake is especially useful when the servo axis needs to maintain its mechanical position while the motor is not producing servo torque. This makes the SJ74AA particularly interesting for vertical axes, lifting mechanisms, positioning systems, and other applications where controlled holding is important.

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2. Brand and Product Series

The MPL family is designed for closed-loop servo applications.

The motor is not intended to operate as an ordinary fixed-speed motor. It normally forms part of a complete motion-control system consisting of the servo motor, compatible servo drive, feedback connection, motion controller, power cables, feedback cables, and mechanical transmission.

The feedback device provides position information while the servo drive regulates motor current and motion.

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3. Detailed Technical Specifications

The torque, power, speed, inertia, frame, and stack values correspond to the B680D motor class.

The exact complete physical envelope and shipping weight can vary with the detailed motor configuration and packaging, so the 40–45 kg class figure is best used for preliminary machine design rather than as a certified shipping value.

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4. Product Dimensions

The MPL-B680D-SJ74AA is a large-frame servo motor.

Its principal mechanical configuration is based on a 215 mm frame and approximately 203.2 mm magnet stack.

The 215 × 203.2 mm figure should be understood as the principal frame and stack dimensions rather than the complete installed envelope.

For actual machine construction, space must also be provided for the shaft, coupling, connector, power cable, feedback cable, mounting hardware, cable bend radius, and brake wiring.

The right-angle connector can be advantageous in compact machine layouts, but sufficient clearance should still be provided around the connector.

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5. Motor Weight

The MPL-B680D-SJ74AA is a large industrial servo motor, and its physical mass should be considered during machine design and installation.

For preliminary engineering purposes, it is reasonable to allow approximately 40–45 kg for the motor configuration.

Because this is a large motor with an integral brake and associated hardware, the actual physical mass should be checked against the individual motor nameplate or dimensional documentation when the installation structure is being finalized.

For machine construction, the mounting plate and lifting arrangement should be designed around the actual motor weight rather than the minimum estimated value.

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6. Model Number Interpretation

The complete model number is:

MPL-B680D-SJ74AA

The major portions of the catalog number can be understood as follows.

This coding structure is useful when comparing similar motors.

For example, the SJ72AA and SJ74AA models have the same basic single-turn feedback configuration, while the final digit distinguishes the brake arrangement.

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7. What Makes the SJ74AA Different?

The most important practical difference between the MPL-B680D-SJ74AA and the closely related MPL-B680D-SJ72AA is the integral brake.

The SJ74AA is therefore particularly attractive when the machine needs a motor-mounted holding brake.

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8. Product Introduction

The MPL-B680D-SJ74AA is a high-power servo motor designed for machines where both dynamic motion control and mechanical holding capability are important.

Its large 215 mm frame and 203.2 mm stack give it a substantial electromagnetic package capable of producing high torque.

At the same time, the motor uses a low-inertia rotor design, allowing the servo system to respond quickly to changes in commanded speed and position.

The single-turn high-resolution encoder provides detailed shaft-position information to the servo drive.

The integral 24 V DC brake adds another layer of functionality. It allows the motor to provide mechanical holding capability when the servo axis is stopped or when servo torque is removed, subject to the application’s safety and control requirements.

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9. High-Torque Performance

The B680D family is primarily a torque-oriented servo motor configuration.

The motor provides approximately 62.8 N·m continuous stall torque and approximately 154.2 N·m peak stall torque.

The continuous torque figure represents the motor’s ability to produce substantial torque on an ongoing basis under the applicable thermal conditions.

The peak torque figure is more relevant to short-duration acceleration, deceleration, indexing, and transient load conditions.

This distinction is important in servo sizing.

A machine that needs high torque continuously should be sized based primarily on continuous torque and thermal requirements rather than simply selecting a motor based on peak torque.

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10. 9.3 kW Power Class

The MPL-B680D-SJ74AA belongs to the approximately 9.3 kW continuous power class.

This power level makes the motor suitable for large machine axes.

It would generally be excessive for a small indexing mechanism, but it becomes useful when a machine must move a heavy load, accelerate a large rotary mass, or maintain substantial torque over an extended operating cycle.

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11. 2000 rpm Speed Class

The D portion of the model indicates the 2000 rpm class.

The motor is therefore oriented toward applications where torque is a higher priority than extremely high rotational speed.

For applications requiring 3000 rpm, a B680F configuration is worth considering.

For applications requiring approximately 3500 rpm, the B680H family provides another alternative.

The B680D remains attractive when the machine’s main requirement is high torque at a moderate servo speed.

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12. Low-Inertia Design

The rotor inertia is approximately:

0.00775 kg·m²

Low rotor inertia is valuable when the machine repeatedly changes speed.

Typical examples include:

• Indexing.
• Start-stop motion.
• Rapid acceleration.
• Rapid deceleration.
• Reversing axes.
• Repeated positioning.

The motor rotor is only one component of the complete inertia calculation.

The inertia of the mechanical load, coupling, gearbox, roller, screw, pulley, or rotary table must also be reflected to the motor shaft.

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13. Single-Turn Absolute Encoder

The S in the model designation indicates the single-turn feedback configuration.

The encoder provides the servo drive with accurate information about the motor shaft position.

This allows the servo system to compare commanded motion with actual motor motion and make corrections accordingly.

The result is much more controlled behavior than would be possible with an open-loop motor.

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14. Single-Turn Feedback Applications

Single-turn absolute feedback is well suited to applications where the important position information is the shaft’s position within one revolution.

Typical examples include:

• Rotary positioning.
• Indexing.
• Servo-driven rollers.
• Machine-tool mechanisms.
• Packaging mechanisms.
• Rotary actuators.
• Industrial automation axes.

For applications where absolute multi-revolution position is required directly from the feedback device, a multi-turn MPL configuration may be more appropriate.

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15. Integral 24 V DC Brake

The integral 24 V DC brake is one of the most important advantages of the SJ74AA configuration.

The brake is primarily intended as a holding device.

It should not automatically be treated as a substitute for the machine’s normal controlled deceleration function.

In a properly designed servo system, the servo drive normally controls deceleration, while the holding brake is used when the axis needs to remain mechanically secured.

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16. Why the Brake Is Useful

The brake can be particularly valuable for vertical or gravity-loaded mechanisms.

Examples include:

• Vertical positioning axes.
• Lifting platforms.
• Z-axis mechanisms.
• Vertical transfer systems.
• Hoisting-related machine axes.
• Elevating work platforms.
• Vertical assembly mechanisms.

When servo power is removed, gravity can cause a vertical load to move.

A suitable holding brake can help prevent unwanted movement, provided it is correctly controlled and the overall machine safety design supports the intended function.

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17. Brake Timing Considerations

When using the integral brake, the machine control sequence should be designed carefully.

A typical servo sequence may involve:

1. Commanding the motor to a controlled stop.
2. Confirming that the axis has reached the required position or standstill condition.
3. Applying the holding brake.
4. Removing servo torque as appropriate.

During startup, the sequence is generally reversed: the servo establishes control before the holding brake is released.

The exact sequence depends on the servo drive, motion controller, machine safety architecture, and application.

The brake should therefore be treated as part of the complete motion-control design rather than as an isolated motor accessory.

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18. Keyed Shaft

The MPL-B680D-SJ74AA uses a keyed shaft extension.

The keyed shaft provides a conventional mechanical connection for industrial equipment.

The coupling should be selected according to the motor’s torque, speed, shaft dimensions, and allowable misalignment.

Poor shaft alignment can lead to excessive bearing load, vibration, coupling wear, and reduced servo performance.

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19. SpeedTEC DIN Connector

The motor uses a right-angle SpeedTEC DIN connector.

The right-angle connector is useful in machine designs where straight connectors would require too much clearance.

The rotatable arrangement allows the connector orientation to be adjusted to suit the motor installation.

However, the final machine design should still allow adequate clearance for cable installation, connector service, and the required cable bend radius.

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20. Mounting Configuration

The motor uses an IEC metric flange mounting arrangement with free mounting holes.

A large servo motor should be mounted to a rigid mechanical structure.

The mounting plate should not be so flexible that motor torque causes significant movement of the motor itself.

Mechanical rigidity is especially important in high-precision positioning applications.

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21. Main Product Advantages

High Continuous Torque

The approximately 62.8 N·m continuous torque provides substantial torque capacity for heavy machine axes.

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High Peak Torque

The approximately 154.2 N·m peak torque provides a significant dynamic reserve during acceleration and transient load conditions.

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9.3 kW Power Class

The motor provides substantial continuous power for large automation systems.

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Single-Turn Absolute Feedback

The high-resolution single-turn encoder supports precise closed-loop servo operation.

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Integrated 24 V DC Brake

The brake adds mechanical holding capability without requiring a separate motor-mounted brake assembly.

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Low-Inertia Rotor

The approximately 0.00775 kg·m² rotor inertia supports responsive servo behavior.

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Keyed Shaft

The keyed shaft provides a familiar and robust industrial mechanical interface.

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Rotatable Right-Angle Connector

The connector arrangement provides useful flexibility during machine installation and cable routing.

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22. Typical Applications

22.1 Packaging Machinery

The MPL-B680D-SJ74AA can be used for larger servo axes in packaging equipment.

Possible functions include:

• Product indexing.
• Heavy feeding mechanisms.
• Rotary positioning.
• Cutting mechanisms.
• Forming mechanisms.
• Large synchronized machine axes.

The integral brake can be particularly useful if the axis must remain securely positioned during a machine stop.

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22.2 Material Handling

Potential applications include:

• Heavy conveyors.
• Transfer systems.
• Roller drives.
• Lifting mechanisms.
• Positioning systems.
• Automated storage machinery.

The high continuous torque is useful when substantial mechanical loads must be moved repeatedly.

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22.3 Vertical Axes

The integral brake makes the motor especially interesting for vertical servo applications.

Examples include:

• Z-axis systems.
• Vertical transfer units.
• Lifting platforms.
• Vertical assembly machinery.
• Elevating mechanisms.
• Gravity-loaded positioning axes.

The exact safety function of the brake must be evaluated according to the machine’s risk assessment and control architecture.

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22.4 Machine Tools

The motor can be used for substantial machine-tool axes and auxiliary positioning mechanisms.

The combination of high torque, low inertia, and high-resolution feedback is useful for controlled servo movement.

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22.5 Printing and Converting

Potential uses include:

• Roller positioning.
• Web handling.
• Indexing.
• Cutting.
• Tension-related motion.
• Synchronized rotary axes.

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22.6 Rotary Tables

Large rotary tables can have substantial inertia.

The B680D’s high torque and peak torque capacity can help accelerate and decelerate such loads.

The brake can also be useful when the table needs to remain mechanically held during a stopped condition.

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23. Applications Where the SJ74AA Is Particularly Attractive

The brake is the feature that makes the SJ74AA particularly valuable when compared with the otherwise similar SJ72AA.

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24. Five Related Models from the Same Series

These models provide useful alternatives depending on whether the application requires a brake, multi-turn feedback, or a higher speed.

The MPL-B680D-SJ72AA is the closest no-brake counterpart.

The MPL-B680D-MJ74AA retains the brake while changing the feedback configuration from single-turn to multi-turn.

The B680F and B680H models move toward higher-speed operation.

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25. Five Same-Brand Commonly Compared Models

These models provide a practical range of comparison points.

The B640F is smaller and lighter.

The B660F sits between the B640F and B680D in physical stack length and torque.

The B680D is the high-torque option in this group.

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26. B640F vs B660F vs B680D

This comparison shows the relationship between frame stack length and torque capability.

The B680D uses the longest stack in this group and consequently provides the highest torque.

The trade-off is increased motor length and weight.

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27. B680D-SJ74AA vs B680D-MJ74AA

The main selection criterion between these two models is the feedback configuration.

If the machine requires single-turn absolute feedback, the SJ74AA is the natural choice.

If multi-revolution absolute position information is required, the MJ74AA becomes the more appropriate alternative.

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28. B680D-SJ74AA vs B680D-SJ72AA

This is one of the simplest comparisons in the MPL range.

The motor performance is broadly similar, while the brake configuration changes the suitability for particular machine designs.

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29. Vertical Axis Applications

The integral brake makes the MPL-B680D-SJ74AA especially useful for vertical axes.

For example, consider a vertical positioning machine carrying a heavy mechanical assembly.

When the servo drive is powered, the motor produces torque and controls the axis.

When the machine stops, the brake can provide holding capability.

This can reduce the dependence on continuous motor torque for maintaining the load in position.

However, the brake should always be integrated into the machine’s overall safety strategy.

For safety-critical applications, the brake should not be treated as the only safety mechanism without a proper risk assessment and suitable control architecture.

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30. Horizontal Axis Applications

The motor is also well suited to horizontal applications.

Examples include:

• Heavy conveyor drives.
• Large rotary positioning axes.
• Packaging axes.
• Machine-tool axes.
• Printing equipment.
• Material-transfer systems.

In these applications, the brake can still be useful during machine shutdown or maintenance, although it may not be as essential as it is for a gravity-loaded vertical axis.

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31. Mechanical Installation Considerations

The large physical size and approximately 40–45 kg weight class should be considered during installation.

The motor should be mounted on a rigid surface.

The flange should be correctly aligned.

Mounting bolts should be appropriately selected.

The driven shaft should be aligned carefully with the motor shaft.

The coupling should be installed without excessive radial or axial force.

Cable routing should not put mechanical stress on the connector.

Adequate clearance should be provided for the brake connector and motor cables.

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32. Thermal Design

High continuous torque means that thermal performance matters.

The actual motor temperature depends on:

• Ambient temperature.
• Load torque.
• Speed.
• Duty cycle.
• Acceleration frequency.
• Deceleration frequency.
• Machine enclosure.
• Cooling conditions.
• Motor mounting.
• Surrounding equipment.

The motor should not be sized solely from the maximum instantaneous load.

The continuous load profile is equally important.

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33. Inertia Matching and Servo Tuning

The motor’s low rotor inertia is useful, but the complete mechanical system still needs to be analyzed.

A machine with a large rotary load may have an inertia many times greater than the motor rotor.

A gearbox can alter the inertia reflected to the motor.

A properly designed servo system should consider:

• Motor rotor inertia.
• Load inertia.
• Gear ratio.
• Coupling inertia.
• Screw inertia.
• Roller inertia.
• Acceleration time.
• Deceleration time.
• Required settling time.
• Mechanical resonance.

These factors have a direct influence on servo tuning and overall positioning performance.

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34. Maintenance

The brushless design means there are no conventional motor brushes that require routine replacement.

Maintenance should instead focus on the complete mechanical and electrical system.

Important inspection points include:

• Motor mounting bolts.
• Shaft coupling.
• Mechanical alignment.
• Bearings.
• Vibration.
• Motor temperature.
• Encoder feedback.
• Power cables.
• Feedback cables.
• Brake wiring.
• Connector condition.
• Servo following error.
• Mechanical backlash.

The brake should also be monitored as part of normal machine maintenance.

A brake that is worn, contaminated, incorrectly adjusted, or improperly controlled may not provide the expected holding performance.

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35. Selection Considerations

When selecting the MPL-B680D-SJ74AA, the following questions should be considered:

Does the machine require approximately 62.8 N·m continuous torque?

If the answer is yes, the B680D family may be appropriate.

Does the machine need approximately 154.2 N·m peak torque?

If high acceleration torque is required, the B680D’s peak capability becomes useful.

Is 2000 rpm sufficient?

If the machine requires significantly higher speed, a B680F or B680H configuration may be a better direction.

Is single-turn feedback sufficient?

If the machine requires multi-turn absolute feedback, the M configuration should be considered instead.

Is an integral brake required?

If yes, the SJ74AA provides the desired 24 V DC brake configuration.

Can the machine accommodate a roughly 40–45 kg motor?

The mounting structure and lifting provisions should be checked before final selection.

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36. Product Selection Guide

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37. Final Technical Summary

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38. Overall Evaluation

The Allen-Bradley MPL-B680D-SJ74AA is a high-torque industrial servo motor designed for demanding motion-control applications.

Its approximately 9.3 kW output, 62.8 N·m continuous torque, 154.2 N·m peak torque, 2000 rpm speed class, and 215 mm × 203.2 mm frame/stack configuration place it firmly in the larger end of the MPL servo motor range.

The motor’s low-inertia rotor helps it respond quickly to changing motion commands, while the single-turn high-resolution absolute encoder provides detailed feedback for closed-loop servo control.

The 24 V DC integral brake is the feature that makes this model especially useful when the machine needs a motor-mounted holding function.

For a heavy horizontal axis where no brake is needed, the MPL-B680D-SJ72AA is the logical comparison.

For a similar motor requiring multi-turn absolute feedback, the MPL-B680D-MJ74AA is a strong alternative.

For higher-speed applications, the B680F and B680H families provide different speed characteristics.

For lower-power machines, the B660F and B640F families can provide a smaller and lighter solution.

Overall, the MPL-B680D-SJ74AA is best suited to large industrial servo axes requiring high torque, accurate single-turn absolute feedback, low-inertia dynamic response, and an integrated 24 V DC holding brake. It is particularly valuable for heavy positioning systems, vertical axes, lifting mechanisms, rotary tables, material-handling equipment, packaging machinery, and other automation equipment where both motion performance and mechanical holding capability are important.