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Allen-Bradley MPL-B420P-HK72AA Low-Inertia Servo Motor

1. Product Overview

The Allen-Bradley MPL-B420P-HK72AA is a high-speed, low-inertia permanent-magnet AC servo motor belonging to the MPL family of low-inertia brushless servo motors. It is designed for precision motion-control applications where high rotational speed, controlled acceleration, repeatable positioning, and compact mechanical construction are important.

The motor uses a 115 mm frame and a 50.8 mm magnetic stack length. It is rated for operation in the 400 V AC voltage class and provides a maximum rated speed of 5000 rpm. The B420P performance class provides approximately 4.74 N·m of continuous torque and approximately 13.5 N·m of peak torque when paired with the appropriate motion-control system.

The HK72AA configuration is particularly identifiable by its keyless shaft, no shaft seal, no integrated brake, and 2000-line incremental encoder feedback. The motor uses a circular DIN / SpeedTec-style right-angle connector that can be rotated through 180 degrees, providing useful flexibility during machine installation and cable routing.

The combination of a relatively compact 115 mm frame, 5000 rpm operating capability, low rotor inertia, and high torque density makes the MPL-B420P-HK72AA suitable for demanding industrial automation equipment requiring repeated rapid motion.

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2. Brand and Product Classification

Item	Specification
Brand	Allen-Bradley
Product Family	MP-Series
Product Series	MPL Low-Inertia Servo Motors
Product Type	Permanent-Magnet AC Servo Motor
Motor Type	Brushless Synchronous Servo Motor
Model	MPL-B420P-HK72AA
Performance Class	B420P
Voltage Class	400 V AC / 460 V class
Frame Size	115 mm
Magnet Stack Length	50.8 mm / 2.0 in
Rated Speed	5000 rpm
Feedback	2000-line incremental encoder
Shaft Configuration	Keyless shaft
Shaft Seal	No shaft seal
Brake	No integrated holding brake
Connector	Circular DIN / SpeedTec, right-angle
Connector Adjustment	180° rotatable
Mounting	IEC metric flange
Motor Construction	Low-inertia permanent-magnet design
Approximate Weight	5.44 kg
Application Category	Industrial motion control

The product belongs to the MPL low-inertia servo motor series, a family intended for high-performance rotary motion applications. The model structure identifies the B420P motor class and the HK72AA configuration, including the keyless shaft, encoder arrangement, connector configuration, and absence of a brake.

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3. Detailed Technical Specifications

Parameter	MPL-B420P-HK72AA Specification
Model	MPL-B420P-HK72AA
Brand	Allen-Bradley
Series	MPL Low-Inertia Servo Motor
Motor Technology	Permanent-magnet synchronous AC servo
Voltage Class	400 V AC
Nominal System Class	460 V class
Phase	Three-phase AC
Rated Speed	5000 rpm
Continuous Torque	Approx. 4.74 N·m
Peak Torque	Approx. 13.5 N·m
Rated Power Class	Approx. 1.9 kW
Feedback	Incremental encoder
Encoder Resolution	2000 lines/revolution
Frame Size	115 mm
Magnet Stack	50.8 mm / 2.0 in
Shaft	Keyless
Shaft Seal	None
Brake	None
Connector	Circular DIN / SpeedTec
Connector Style	Right-angle
Connector Rotation	180° rotatable
Mounting Flange	IEC metric
Mounting Type	Free mounting holes / metric flange
Rotor Inertia	Approx. 0.00026 kg·m²
Weight	Approx. 5.44 kg
Enclosure / Mechanical Configuration	Servo motor for industrial motion applications
Feedback Type	Incremental
Typical Drive Environment	Servo drive / motion-control system
Primary Use	High-speed positioning and coordinated motion

The 4.74 N·m continuous torque and approximately 13.5 N·m peak torque correspond to the B420P motor class. The published performance data for this motor class also identifies approximately 1.9 kW output capability, 5000 rpm rated speed, and rotor inertia of approximately 0.00026 kg·m².

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4. Dimensions and Weight

Mechanical dimensions are especially important when replacing an existing servo motor or designing a new machine. The MPL-B420P-HK72AA uses a 115 mm frame size with a 50.8 mm magnetic stack length. These two dimensions define the primary motor size classification.

Dimension / Mechanical Parameter	Specification
Model	MPL-B420P-HK72AA
Frame Size	115 mm
Frame Size in Inches	Approx. 4.53 in
Magnet Stack Length	50.8 mm
Magnet Stack Length in Inches	2.0 in
Shaft Type	Keyless
Shaft Key	Not included
Shaft Seal	Not included
Mounting Standard	IEC metric
Mounting Flange	Metric flange
Connector Orientation	Right-angle
Connector Rotation	180°
Approximate Weight	5.44 kg
Overall Motor Length	Configuration/drawing dependent
Overall Shaft Projection	Refer to mechanical drawing for installation
Mounting Hole Dimensions	Refer to applicable mechanical drawing

The 115 mm frame size should be used as the principal dimensional reference when evaluating machine compatibility. The 50.8 mm magnet-stack length is the second major dimensional identifier within the MPL-B420P family.

For an actual replacement installation, the complete mechanical drawing should be checked for shaft projection, flange dimensions, bolt-circle dimensions, connector clearance, and overall motor length rather than relying only on the frame size.

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5. Product Series

The MPL-B420P-HK72AA belongs to the MPL Low-Inertia Servo Motor Series within the MP-Series product family.

The MPL series is designed around permanent-magnet brushless servo technology. Its low-inertia construction is intended to reduce the amount of rotational energy that must be accelerated or decelerated during rapid changes in speed.

This characteristic is particularly useful in machines that perform frequent indexing, short-distance positioning, reciprocating movement, rapid acceleration, or repeated start-stop cycles.

The B420P motor class occupies a medium-to-high performance position within the 5000 rpm MPL family. For comparison, the B310P, B320P, B330P, B420P, and B430P models cover progressively higher torque and power levels while retaining the 5000 rpm class.

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6. Understanding the MPL-B420P-HK72AA Model Number

The model number contains several useful configuration identifiers.

Model Code	Meaning
MPL	Low-inertia servo motor family
B	Voltage / motor family designation
4	115 mm frame class
20	50.8 mm magnetic stack class
P	5000 rpm performance class
H	Incremental encoder configuration
K	Keyless shaft
7	Circular SpeedTec DIN connector, right-angle, rotatable
2	No brake
AA	Configuration / option designation

The K designation is particularly important because it identifies the motor as a keyless-shaft configuration. This distinguishes the HK72AA from comparable HJ configurations that use a keyed shaft.

The final 2 in the HK72AA configuration identifies the no-brake arrangement. Therefore, the HK72AA should not be treated as interchangeable with a brake-equipped configuration without checking the complete electrical and mechanical requirements.

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7. Motor Performance

The MPL-B420P-HK72AA is designed for applications where speed and dynamic response are more important than simply maximizing continuous torque.

Its 5000 rpm rating allows the motor to support high-speed machine axes, rotating mechanisms, indexing systems, feed mechanisms, and other automated equipment where a relatively high operating speed is required.

The B420P motor class provides approximately 4.74 N·m of continuous torque and approximately 13.5 N·m of peak torque. The difference between continuous and peak torque allows the motor to handle short-duration acceleration or transient loads above its continuous operating torque level.

The motor’s low rotor inertia is another important characteristic. A rotor inertia of approximately 0.00026 kg·m² helps the servo system respond efficiently to changes in commanded speed and position.

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8. Continuous Torque

The continuous torque rating is approximately 4.74 N·m.

Continuous torque represents the approximate torque level the motor can deliver during sustained operation under specified operating conditions.

In practical machine design, continuous torque should be compared with the actual RMS torque requirement of the axis. A machine that repeatedly accelerates, decelerates, stops, and reverses should not be evaluated solely from its instantaneous maximum torque requirement.

For applications with frequent acceleration and deceleration, the servo sizing process should consider both the continuous thermal load and short-duration peak torque requirements.

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9. Peak Torque

The B420P motor class provides approximately 13.5 N·m of peak torque.

Peak torque is useful during acceleration, deceleration, rapid positioning, load disturbances, and other short-duration dynamic events.

The peak torque rating should not be interpreted as a continuous operating torque. The actual allowable peak duration depends on the motor, drive, duty cycle, ambient conditions, and motion profile.

For machine designers, the important advantage is the substantial difference between continuous torque and peak torque. This provides additional dynamic capability without requiring the motor to operate continuously at its peak level.

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10. Rated Speed

The MPL-B420P-HK72AA is rated for approximately 5000 rpm.

A 5000 rpm servo motor can be useful in applications where high linear speed is required from a screw, pulley, roller, spindle-like mechanism, or other rotating transmission.

The actual machine speed should always be calculated from the mechanical transmission ratio.

For example, a servo motor connected to a gearbox, timing belt, ball screw, or direct-drive mechanism may operate at 5000 rpm while producing a much lower output speed at the machine load.

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11. 1.9 kW Power Class

The B420P motor class is approximately 1.9 kW.

The power rating provides a convenient reference when comparing the B420P with other motors in the MPL family.

A motor with approximately 1.9 kW output capability can be suitable for a wide range of automated equipment, but actual motor selection should be based on load torque, acceleration time, duty cycle, reflected inertia, maximum speed, and required positioning accuracy rather than power alone.

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12. Low-Inertia Motor Construction

Low inertia is one of the main characteristics of the MPL series.

When a servo motor changes speed rapidly, the drive must accelerate or decelerate the rotating mass of the motor rotor as well as the reflected mechanical load.

Lower rotor inertia can reduce the amount of energy required to change motor speed. This can help the servo system respond quickly to changing motion commands.

The approximately 0.00026 kg·m² rotor inertia of the B420P motor class is therefore an important specification for high-dynamic applications.

Low inertia can be particularly useful for:

• Pick-and-place mechanisms
• High-speed indexing equipment
• Packaging machinery
• Electronic assembly machines
• Labeling systems
• Printing equipment
• Material handling axes
• Fast reciprocating mechanisms
• Automated inspection systems
• Coordinated multi-axis machinery

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13. Encoder and Feedback System

The MPL-B420P-HK72AA uses a 2000-line incremental encoder.

The encoder provides feedback to the servo drive so that the control system can determine motor position and speed.

The incremental encoder arrangement is appropriate for conventional closed-loop servo applications where the motion controller and drive use feedback information to regulate the motor.

The 2000-line feedback specification provides a substantial amount of position information per motor revolution and supports precise servo control when used with an appropriate drive and control architecture.

It is important to distinguish the HK72AA from other B420P configurations that use single-turn or multi-turn absolute feedback. Those versions may have different encoder architectures and should not automatically be considered electrical drop-in replacements.

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14. Keyless Shaft Configuration

The MPL-B420P-HK72AA uses a keyless shaft.

A keyless shaft can be advantageous when the mechanical coupling is designed around an appropriate clamp, hub, or other locking mechanism.

Compared with a keyed shaft, a keyless arrangement can provide a clean cylindrical shaft interface and may be suitable for machine designs where the coupling system does not require a traditional shaft key.

The absence of a shaft key is an important replacement consideration. A machine originally designed for a keyed motor may require a different coupling or hub when using the HK72AA.

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15. No Shaft Seal

The HK72AA is specified without a shaft seal.

This should be considered during machine design, particularly when the motor is installed in an environment containing significant dust, liquid contamination, washdown exposure, oil mist, or other potentially aggressive contaminants.

The motor’s environmental suitability should be evaluated against the actual machine environment before installation.

A shaft-seal requirement can also affect the choice between different MPL configurations.

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16. No Integrated Holding Brake

The MPL-B420P-HK72AA is a non-brake configuration.

This means that the motor does not include an integrated 24 V DC holding brake.

The absence of a brake can be useful for applications where a holding brake is not necessary and where reduced motor configuration complexity is desirable.

However, applications involving vertical axes, suspended loads, or mechanisms that must remain stationary when servo power is removed may require an independent braking or mechanical holding solution.

When comparing the HK72AA with a brake-equipped B420P model, the machine designer should evaluate both electrical wiring and mechanical safety requirements.

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17. Connector Configuration

The motor uses a circular DIN / SpeedTec connector in a right-angle configuration.

The connector can be rotated through approximately 180 degrees, providing additional flexibility for cable routing.

This can be valuable when the servo motor is installed in a compact machine where a fixed connector direction could interfere with:

• Motor mounting
• Cable trays
• Machine guards
• Adjacent motors
• Linear slides
• Gearboxes
• Safety covers
• Pneumatic components
• Cooling arrangements

The rotatable connector arrangement can simplify machine wiring and help reduce excessive cable bending.

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18. Mounting Arrangement

The MPL-B420P-HK72AA uses an IEC metric mounting flange.

The mounting structure is designed for industrial machine installation and provides a standard mechanical interface for mounting the motor to the machine frame, gearbox, actuator, or other driven mechanism.

When replacing a motor, the mounting interface must be checked carefully. Matching the frame size alone does not guarantee mechanical interchangeability.

The following should be verified:

• Mounting flange dimensions
• Mounting hole pattern
• Shaft diameter
• Shaft projection
• Coupling type
• Connector clearance
• Overall motor length
• Available installation space
• Load direction
• Radial loading
• Axial loading

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19. Main Applications

Packaging Machinery

The MPL-B420P-HK72AA can be used in packaging machines that require repeated high-speed positioning and coordinated movement.

Typical applications include indexing conveyors, film-feed mechanisms, cutting mechanisms, sealing mechanisms, product positioning systems, and automated packaging axes.

The 5000 rpm rating and low-inertia construction are particularly useful where the axis must accelerate and decelerate repeatedly.

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Pick-and-Place Equipment

High-speed pick-and-place mechanisms can benefit from a servo motor capable of rapid changes in velocity.

The low-inertia motor construction can help the control system manage rapid acceleration and deceleration cycles.

Applications may include robotic transfer systems, tray loading, component placement, and automated material movement.

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Conveyor Systems

Servo-driven conveyors require controlled acceleration, precise positioning, and coordinated movement.

The MPL-B420P-HK72AA can be used for indexing conveyors, synchronized transfer systems, positioning conveyors, and automated product-handling equipment.

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Printing and Labeling Equipment

Printing and labeling systems often require controlled speed and accurate synchronization.

Servo motors can be used to control rollers, feed mechanisms, positioning systems, and registration axes.

The 5000 rpm speed capability makes the B420P class suitable for applications requiring relatively fast rotational operation.

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Assembly Automation

Automated assembly machines frequently use servo motors for insertion, indexing, rotary positioning, feeding, and transfer mechanisms.

The MPL-B420P-HK72AA can provide a combination of continuous torque, peak torque, and high rotational speed suitable for these applications.

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Material Handling

Material-handling machinery can use servo motors for controlled movement of belts, rollers, positioning axes, and transfer mechanisms.

The motor is particularly suited to applications where the load must repeatedly move between predefined positions.

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Machine Tools and Processing Equipment

Servo motors can be used in machine-tool auxiliary axes, feed mechanisms, indexing systems, and automated positioning equipment.

The exact suitability depends on required torque, speed, load inertia, environmental conditions, and mechanical transmission.

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20. Product Advantages

20.1 High-Speed Operation

The 5000 rpm rating provides substantial speed capability for industrial motion systems.

This can help reduce cycle times in applications where the mechanical transmission is designed to take advantage of higher motor speed.

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20.2 Low-Inertia Response

The low-inertia rotor design is useful for applications involving rapid acceleration and deceleration.

This is one of the most important advantages of the MPL product family.

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20.3 High Torque Density

The B420P class provides approximately 4.74 N·m continuous torque and approximately 13.5 N·m peak torque in a 115 mm frame class.

This provides a useful combination of compact physical size and dynamic torque capability.

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20.4 Compact 115 mm Frame

The 115 mm frame provides a practical balance between motor size and performance.

The 50.8 mm magnetic stack further identifies the motor’s physical configuration within the MPL family.

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20.5 Incremental Encoder Feedback

The 2000-line incremental encoder provides closed-loop feedback for servo motion control.

This supports controlled positioning, velocity regulation, acceleration management, and coordinated machine operation.

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20.6 Keyless Shaft

The keyless shaft configuration can simplify certain coupling arrangements.

It is particularly suitable for machine builders who prefer clamp-style or other keyless mechanical coupling systems.

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20.7 Rotatable Connector

The 180-degree rotatable right-angle connector provides installation flexibility.

This is useful in compact automation systems where cable direction and machine access are important considerations.

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20.8 No-Brake Configuration

The no-brake configuration can simplify applications that do not require a motor holding brake.

It can also be useful where the machine uses an independent mechanical holding mechanism.

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21. Five Related or Same-Series Models

The following models are closely related to the MPL-B420P-HK72AA. They use the same general B420P motor class while differing in feedback, shaft, brake, or other configuration details.

Model	Frame	Stack	Speed	Feedback	Shaft	Brake	Approx. Power	Weight
MPL-B420P-HK74AA	115 mm	50.8 mm	5000 rpm	2000-line incremental	Keyless	Brake-equipped configuration	Approx. 1.9 kW	Configuration-dependent
MPL-B420P-HJ72AA	115 mm	50.8 mm	5000 rpm	2000-line incremental	Keyed	No brake	Approx. 1.9 kW	Configuration-dependent
MPL-B420P-HJ74AA	115 mm	50.8 mm	5000 rpm	2000-line incremental	Keyed	Brake-equipped configuration	Approx. 1.9 kW	Approx. 7.29 kg
MPL-B420P-MK72AA	115 mm	50.8 mm	5000 rpm	Multi-turn absolute	Keyless	No brake	Approx. 1.9 kW	Configuration-dependent
MPL-B420P-SJ72AA	115 mm	50.8 mm	5000 rpm	Single-turn high-resolution	Keyed	No brake	Approx. 1.9 kW	Configuration-dependent

The B420P configuration family includes multiple combinations of feedback type, shaft type, connector arrangement, and brake option. The existence of the HK72AA, HK74AA, HJ72AA, HJ74AA, MK72AA, SJ72AA and other configurations is documented in the product family listings.

For example, the MK72AA uses multi-turn high-resolution absolute feedback and a keyless shaft, while the SJ72AA uses single-turn high-resolution feedback with a keyed shaft and no brake.

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22. B420P Configuration Comparison

Model	Feedback	Shaft	Brake	Main Difference
MPL-B420P-HK72AA	Incremental	Keyless	No	Reference model
MPL-B420P-HK74AA	Incremental	Keyless	Yes	Adds brake
MPL-B420P-HJ72AA	Incremental	Keyed	No	Keyed shaft
MPL-B420P-HJ74AA	Incremental	Keyed	Yes	Keyed shaft + brake
MPL-B420P-MK72AA	Multi-turn absolute	Keyless	No	Absolute multi-turn feedback
MPL-B420P-MJ72AA	Multi-turn absolute	Keyed	No	Absolute feedback + keyed shaft
MPL-B420P-MJ74AA	Multi-turn absolute	Keyed	Yes	Absolute feedback + brake
MPL-B420P-SJ72AA	Single-turn absolute/high-resolution	Keyed	No	Single-turn feedback
MPL-B420P-SJ74AA	Single-turn absolute/high-resolution	Keyed	Yes	Single-turn feedback + brake

This comparison illustrates why the final characters of the model number are important. Two motors may share the same frame, stack length, speed, and general power class while having significantly different feedback and mechanical configurations.

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23. Five Representative Same-Brand Models

The following five models are representative models from the same Allen-Bradley MPL family and are useful when comparing different motor performance levels.

Model	Speed	Continuous Torque	Peak Torque	Power	Rotor Inertia	Approx. Weight
MPL-B310P	5000 rpm	1.58 N·m	3.61 N·m	0.77 kW	0.000044 kg·m²	2.7 kg
MPL-B320P	5000 rpm	3.05 N·m	7.91 N·m	1.5 kW	0.000078 kg·m²	3.7 kg
MPL-B330P	5000 rpm	4.18 N·m	11.1 N·m	1.8 kW	0.00012 kg·m²	4.6 kg
MPL-B420P	5000 rpm	4.74 N·m	13.5 N·m	1.9 kW	0.00026 kg·m²	Approx. 4.3 kg family data
MPL-B430P	5000 rpm	6.55 N·m	19.8 N·m	2.2 kW	0.00038 kg·m²	5.5 kg

The performance data shows the progression from the smaller B310P through B320P, B330P, B420P, and B430P models. The B420P provides a useful middle-to-upper position in this group, with approximately 4.74 N·m continuous torque, 13.5 N·m peak torque, and 1.9 kW output class.

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24. Same-Series Performance Comparison

Model	Rated Speed	Continuous Torque	Peak Torque	Power	Typical Position in Family
MPL-B310P	5000 rpm	1.58 N·m	3.61 N·m	0.77 kW	Lower power
MPL-B320P	5000 rpm	3.05 N·m	7.91 N·m	1.5 kW	Lower-middle power
MPL-B330P	5000 rpm	4.18 N·m	11.1 N·m	1.8 kW	Middle power
MPL-B420P	5000 rpm	4.74 N·m	13.5 N·m	1.9 kW	Medium-high power
MPL-B430P	5000 rpm	6.55 N·m	19.8 N·m	2.2 kW	Higher power

This comparison is useful when determining whether the B420P is appropriately sized for an application.

If the application requires significantly less torque, a smaller B310P or B320P may be sufficient.

If the application requires torque above the B420P range, the B430P provides a higher torque class while maintaining a 5000 rpm rating.

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25. Application Selection Guide

Application Requirement	Suitable Consideration
High-speed indexing	MPL-B420P-HK72AA
Rapid acceleration	MPL-B420P-HK72AA
Keyless coupling	MPL-B420P-HK72AA
No holding brake required	MPL-B420P-HK72AA
Incremental feedback required	MPL-B420P-HK72AA
Keyed shaft required	B420P-HJ configuration
Holding brake required	B420P-HK74 / HJ74 configuration
Multi-turn absolute feedback	B420P-MK / MJ configuration
Single-turn absolute feedback	B420P-SJ / SK configuration
Lower torque requirement	B310P / B320P
Medium torque requirement	B330P
Higher torque requirement	B430P

The HK72AA is particularly appropriate when the machine requires a high-speed, low-inertia motor with incremental feedback and a keyless shaft, while not requiring an integrated holding brake.

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26. Typical Equipment

The MPL-B420P-HK72AA can be considered for many types of industrial automation equipment, including:

• Automatic packaging machines
• Cartoning machines
• Wrapping machines
• Labeling machines
• Filling equipment
• Indexing machines
• Pick-and-place systems
• Assembly machines
• Automated inspection machines
• Conveyor positioning systems
• Material handling systems
• Printing machinery
• Web handling equipment
• Cutting systems
• Feeding mechanisms
• Transfer mechanisms
• Rotary indexing tables
• Automated production lines
• High-speed positioning systems
• Multi-axis automation equipment

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27. Advantages for High-Speed Automation

High-speed automation places greater demands on the servo system than simple constant-speed operation.

The motor must repeatedly accelerate, decelerate, stop, reverse, and return to a commanded position.

The 5000 rpm rating of the MPL-B420P motor class provides sufficient speed capability for many high-speed machine axes.

The low-inertia design further supports dynamic operation because the servo drive does not have to accelerate an excessively large motor rotor during every motion cycle.

This can be particularly useful when the machine performs hundreds or thousands of repeated motion cycles.

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28. Advantages for Positioning Applications

The 2000-line incremental encoder provides motor feedback for closed-loop motion control.

Positioning performance depends on the complete servo system, including the motor, encoder, drive, controller, mechanical transmission, coupling, load inertia, and tuning.

The motor therefore should be viewed as one part of the overall motion-control system.

When correctly matched with the drive and machine mechanics, the MPL-B420P-HK72AA can provide precise and repeatable rotary motion suitable for industrial automation.

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29. Advantages of the Keyless Shaft

The keyless shaft is one of the most significant differences between the HK72AA and keyed B420P configurations.

A keyless shaft can be advantageous when the machine uses:

• Clamp-style couplings
• Keyless hubs
• Precision shaft couplings
• Special rotary transmission components
• Compact mechanical connections

However, the coupling must be correctly selected for the motor’s torque and speed requirements.

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30. Advantages of the No-Brake Design

The absence of a brake makes the HK72AA appropriate for applications where the motor does not need to mechanically hold a load when servo power is removed.

This can be useful for horizontal axes and other mechanisms where gravity does not create an uncontrolled load movement.

For vertical axes or suspended loads, the machine designer should evaluate whether a holding brake or another independent mechanical safety mechanism is necessary.

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31. Maintenance Considerations

Servo motors generally require less routine maintenance than conventional mechanical systems because there are fewer wear components inside the motor.

Nevertheless, installation and operating conditions remain important.

Particular attention should be given to:

• Cable condition
• Connector condition
• Shaft coupling alignment
• Mounting bolt condition
• Motor temperature
• Mechanical vibration
• Radial load
• Axial load
• Environmental contamination
• Encoder feedback integrity
• Drive fault history

The absence of a shaft seal should also be considered when evaluating the environmental conditions around the motor shaft.

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32. Mechanical Installation Considerations

The motor should be installed on a rigid and accurately aligned machine structure.

Misalignment between the motor shaft and driven equipment can introduce excessive radial or axial forces.

Possible consequences include:

• Increased bearing load
• Excessive vibration
• Coupling wear
• Encoder errors
• Increased motor temperature
• Reduced service life
• Unexpected servo faults

The connector should also have sufficient clearance to prevent cable bending beyond the recommended radius.

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33. Servo Drive Selection Considerations

The MPL-B420P-HK72AA is intended to operate as part of a servo motion-control system.

Drive selection should consider:

• Motor voltage class
• Continuous current requirement
• Peak current requirement
• Encoder feedback compatibility
• Motor cable compatibility
• Required speed
• Required torque
• Regeneration requirements
• Motion-controller architecture
• Application duty cycle
• Safety requirements

A motor should not be selected solely on the basis of nominal power.

The correct combination of motor, drive, feedback, mechanical load, and motion profile is essential for reliable operation.

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34. Load and Inertia Matching

Servo sizing should consider reflected load inertia.

A motor can have sufficient torque and still perform poorly if the reflected load inertia is not appropriate for the control system.

The mechanical transmission ratio has a significant effect on reflected inertia.

Gearboxes, belt drives, ball screws, pulleys, and other transmission systems can transform the effective inertia seen by the motor.

For high-speed positioning systems, inertia matching is particularly important because excessive reflected inertia can reduce dynamic response and make servo tuning more difficult.

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35. Brake Selection Versus Non-Brake Selection

The HK72AA is a non-brake motor.

When comparing it with an HK74AA or HJ74AA configuration, the key difference is the inclusion of a motor holding brake in the brake-equipped configuration.

Requirement	HK72AA	Brake-Equipped Configuration
High-speed operation	Yes	Yes
Low-inertia design	Yes	Yes
Incremental feedback	Yes	Depending on configuration
Keyless shaft	Yes	Available in HK configuration
Holding brake	No	Yes
Vertical load holding	Requires separate solution	Brake may provide holding function subject to application requirements
Mechanical coupling	Keyless	Depends on model
Motor class	B420P	B420P

The choice should be based on the machine’s mechanical and safety requirements rather than simply selecting the model with more options.

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36. Why the MPL-B420P-HK72AA Can Be Considered for High-Dynamic Applications

The motor combines several characteristics that are useful in high-dynamic motion control:

• 5000 rpm speed capability
• Approximately 4.74 N·m continuous torque
• Approximately 13.5 N·m peak torque
• Approximately 1.9 kW output class
• Low rotor inertia
• Incremental encoder feedback
• Compact 115 mm frame
• Keyless shaft
• No integrated brake
• Rotatable right-angle connector

These characteristics make the motor particularly suitable for machinery where the axis must change speed quickly and repeatedly.

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37. Comparison with Smaller MPL Motors

Compared with the B310P, the B420P provides substantially greater torque and power capability.

Compared with the B320P, the B420P provides a higher continuous torque rating and higher peak torque capability.

Compared with the B330P, the B420P provides a moderate increase in torque and power while maintaining the same 5000 rpm class.

Compared with the B430P, the B420P has a lower torque and power rating, making the B430P more appropriate when the machine requires a higher torque class.

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38. Detailed Same-Brand Model Reference Table

Model	Speed	Continuous Torque	Peak Torque	Power	Inertia	Weight
MPL-B310P	5000 rpm	1.58 N·m	3.61 N·m	0.77 kW	0.000044 kg·m²	2.7 kg
MPL-B320P	5000 rpm	3.05 N·m	7.91 N·m	1.5 kW	0.000078 kg·m²	3.7 kg
MPL-B330P	5000 rpm	4.18 N·m	11.1 N·m	1.8 kW	0.00012 kg·m²	4.6 kg
MPL-B420P	5000 rpm	4.74 N·m	13.5 N·m	1.9 kW	0.00026 kg·m²	Approx. 4.3 kg
MPL-B430P	5000 rpm	6.55 N·m	19.8 N·m	2.2 kW	0.00038 kg·m²	5.5 kg

These models provide a useful reference range for servo motor selection within the same low-inertia product family.

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39. Five Related Model Selection Reference

Model	Main Configuration	Feedback	Shaft	Brake	Frame	Stack
MPL-B420P-HK72AA	Reference model	Incremental	Keyless	No	115 mm	50.8 mm
MPL-B420P-HK74AA	Keyless brake version	Incremental	Keyless	Yes	115 mm	50.8 mm
MPL-B420P-HJ72AA	Keyed no-brake version	Incremental	Keyed	No	115 mm	50.8 mm
MPL-B420P-HJ74AA	Keyed brake version	Incremental	Keyed	Yes	115 mm	50.8 mm
MPL-B420P-MK72AA	Absolute feedback version	Multi-turn	Keyless	No	115 mm	50.8 mm

The five models above are closely related because they share the B420P motor class and basic mechanical envelope while changing the feedback, shaft, and brake configuration.

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40. Recommended Model by Mechanical Requirement

Machine Requirement	Suggested Model Family
Keyless shaft + incremental feedback + no brake	MPL-B420P-HK72AA
Keyless shaft + incremental feedback + brake	MPL-B420P-HK74AA
Keyed shaft + incremental feedback + no brake	MPL-B420P-HJ72AA
Keyed shaft + incremental feedback + brake	MPL-B420P-HJ74AA
Keyless shaft + multi-turn absolute feedback	MPL-B420P-MK72AA
Keyed shaft + single-turn feedback	MPL-B420P-SJ72AA

This configuration approach is generally more useful than selecting a motor by model number alone. The shaft, encoder, brake, connector, voltage class, and mechanical dimensions should all be matched to the machine.

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41. Product Advantages Summary

Advantage	Description
High Speed	5000 rpm rating supports fast rotary motion
Low Inertia	Supports rapid acceleration and deceleration
High Torque Density	Approx. 4.74 N·m continuous torque in the B420P class
High Peak Capability	Approx. 13.5 N·m peak torque
Compact Frame	115 mm frame size
Incremental Feedback	2000-line encoder
Keyless Shaft	Suitable for compatible keyless coupling systems
No Brake	Appropriate for applications without a holding-brake requirement
Flexible Connector	Right-angle circular connector with 180° rotation
Industrial Mounting	IEC metric flange
Broad Application Range	Packaging, assembly, indexing, material handling, and other automation

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42. Technical Specification Summary

Category	Detailed Specification
Model	MPL-B420P-HK72AA
Brand	Allen-Bradley
Family	MP-Series
Series	MPL Low-Inertia Servo Motors
Motor Type	Brushless permanent-magnet AC servo motor
Voltage Class	400 V AC
System Class	460 V
Rated Speed	5000 rpm
Continuous Torque	Approx. 4.74 N·m
Peak Torque	Approx. 13.5 N·m
Power	Approx. 1.9 kW
Frame	115 mm
Stack	50.8 mm / 2.0 in
Feedback	2000-line incremental encoder
Shaft	Keyless
Shaft Seal	None
Brake	None
Connector	Circular DIN / SpeedTec
Connector Direction	Right-angle
Connector Rotation	180°
Mounting	IEC metric
Rotor Inertia	Approx. 0.00026 kg·m²
Weight	Approx. 5.44 kg
Overall Dimensions	Configuration-dependent; 115 mm frame and 50.8 mm stack
Main Application	High-speed industrial motion control
Typical Machines	Packaging, indexing, assembly, material handling, positioning, printing and automation equipment

The published model-specific specifications identify the HK72AA as a 400 V, 115 mm, 50.8 mm-stack, 5000 rpm, 2000-line incremental-feedback motor with a keyless shaft, no shaft seal, no brake, and a circular right-angle DIN connector. The listed model weight is approximately 12 lb, equivalent to approximately 5.44 kg.

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43. Final Product Description

The Allen-Bradley MPL-B420P-HK72AA is a high-speed, low-inertia permanent-magnet AC servo motor designed for industrial automation and precision motion-control applications.

It combines a 115 mm frame, 50.8 mm magnetic stack, 5000 rpm rated speed, approximately 4.74 N·m continuous torque, approximately 13.5 N·m peak torque, and approximately 1.9 kW power capability. The motor uses a 2000-line incremental encoder for closed-loop feedback and features a keyless shaft without a shaft seal or integrated holding brake.

The low-inertia construction makes the motor well suited to applications requiring frequent acceleration and deceleration. This includes high-speed indexing, packaging, pick-and-place equipment, assembly machinery, material handling, automated inspection, and other servo-driven production equipment.

The keyless shaft provides flexibility for compatible coupling systems, while the right-angle circular DIN connector with 180-degree rotation provides additional flexibility during machine installation and cable routing.

For applications that do not require an integrated motor brake, the HK72AA provides a relatively straightforward B420P configuration. When a brake, keyed shaft, or absolute feedback is required, closely related B420P configurations can be selected instead.

The MPL-B420P-HK72AA is therefore best understood as a 5000 rpm, approximately 1.9 kW, low-inertia servo motor in the B420P performance class, using incremental feedback, a keyless shaft, and a no-brake configuration.

For replacement work, the most important points to verify are the 115 mm frame, 50.8 mm stack, 5000 rpm speed, feedback type, keyless shaft, no-brake configuration, connector arrangement, mounting dimensions, cable requirements, and actual machine load profile.