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Allen-Bradley MPL-B420P-HK74AA Low-Inertia Servo Motor
1. Product Overview
The Allen-Bradley MPL-B420P-HK74AA is a high-speed, low-inertia permanent-magnet AC servo motor designed for industrial motion-control and automated machinery applications.
It belongs to the MP-Series MPL Low-Inertia Servo Motor family and uses a 115 mm frame with a 50.8 mm magnetic stack. The motor is designed for operation in the 460/480 V AC class and has a 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, depending on the drive and operating conditions.
The HK74AA configuration combines a keyless shaft, 2000-line incremental encoder, 24 V DC holding brake, and right-angle circular SpeedTec DIN connector. The connector can be rotated through approximately 180 degrees, which provides useful flexibility when routing motor and feedback cables inside compact automation equipment.
The motor has a low-inertia rotor design intended for applications involving frequent acceleration, deceleration, indexing, positioning, and speed changes.
2. Brand and Product Classification
| Item | Specification |
|---|---|
| Brand | Allen-Bradley |
| Product Family | MP-Series |
| Product Series | MPL Low-Inertia Servo Motors |
| Product Type | AC Servo Motor |
| Motor Technology | Permanent-Magnet Brushless Servo Motor |
| Model | MPL-B420P-HK74AA |
| Performance Class | B420P |
| Voltage Class | 460/480 V AC |
| Frame Size | 115 mm |
| Magnet Stack Length | 50.8 mm / 2.0 in |
| Rated Speed | 5000 rpm |
| Continuous Torque | Approx. 4.74 N·m |
| Peak Torque | Approx. 13.5 N·m |
| Power Class | Approx. 1.9 kW |
| Feedback | Incremental Encoder |
| Encoder Resolution | 2000 lines/revolution |
| Shaft | Keyless |
| Shaft Seal | No shaft seal |
| Brake | 24 V DC Holding Brake |
| Connector | Circular SpeedTec DIN |
| Connector Style | Right-angle |
| Connector Rotation | 180° rotatable |
| Mounting | IEC Metric |
| Mounting Type | Free Mounting Holes / Type FF |
| Rotor Inertia | Approx. 0.00026 kg·m² |
| Approximate Weight | 6.80 kg |
| Main Application | Industrial motion control |
The product is classified as a low-inertia brushless servo motor. Its combination of high speed, moderate-to-high torque, incremental feedback, and holding brake makes it suitable for demanding automated motion systems.
3. Detailed Technical Specifications
| Parameter | MPL-B420P-HK74AA Specification |
|---|---|
| Model | MPL-B420P-HK74AA |
| Brand | Allen-Bradley |
| Product Family | MP-Series |
| Product Series | MPL Low-Inertia Servo Motors |
| Motor Type | Brushless Permanent-Magnet AC Servo |
| Voltage | 460/480 V AC class |
| Voltage Type | AC |
| Phase | Three-phase |
| 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 |
| 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 |
| Feedback | Incremental Encoder |
| Encoder Resolution | 2000 lines/revolution |
| Shaft Configuration | Keyless |
| Shaft Key | None |
| Shaft Seal | None |
| Holding Brake | 24 V DC |
| Connector | Circular SpeedTec DIN |
| Connector Orientation | Right-angle |
| Connector Rotation | 180° rotatable |
| Mounting Standard | IEC Metric |
| Mounting Type | Free Mounting Holes, Type FF |
| Rotor Inertia | Approx. 0.00026 kg·m² |
| Enclosure Classification | IP20 / NEMA 1 class configuration |
| Approximate Weight | 6.80 kg |
| Operating Temperature Range | Approx. 0 to 40 °C |
| Typical Humidity Range | 5–95%, non-condensing |
| Typical Maximum Installation Altitude | Approx. 1000 m |
| Overall Envelope | Configuration-dependent |
| Primary Function | Precision rotary motion control |
The B420P motor class is rated at approximately 4.74 N·m continuous torque, 13.5 N·m peak torque, 1.9 kW power, and 5000 rpm. The published family data also lists approximately 0.00026 kg·m² rotor inertia for the B420P class.
4. Dimensions and Mechanical Specifications
The MPL-B420P-HK74AA uses a 115 mm frame and a 50.8 mm magnet stack.
These are the primary dimensional identifiers for the motor.
| Mechanical Parameter | Specification |
|---|---|
| Model | MPL-B420P-HK74AA |
| Frame Size | 115 mm |
| Frame Size | Approx. 4.53 in |
| Magnet Stack Length | 50.8 mm |
| Magnet Stack Length | 2.0 in |
| Shaft Type | Keyless |
| Shaft Key | None |
| Shaft Seal | None |
| Mounting Standard | IEC Metric |
| Mounting Type | Free Mounting Holes |
| Mounting Flange Type | Type FF |
| Connector | Right-angle circular DIN |
| Connector Rotation | 180° |
| Brake | Integrated 24 V DC holding brake |
| Approximate Weight | 6.80 kg |
| Overall Motor Length | Refer to applicable mechanical drawing |
| Overall Shaft Projection | Refer to applicable mechanical drawing |
| Mounting Hole Dimensions | Refer to applicable mechanical drawing |
The 115 mm frame size should be used as the primary dimensional reference when comparing the motor with another B420P configuration.
The 50.8 mm magnetic stack identifies the motor’s stack-length class.
The exact overall motor length, shaft projection, mounting-hole geometry, and connector clearance should be checked against the applicable mechanical drawing when the motor is being installed as a replacement.
5. Product Series
The MPL-B420P-HK74AA belongs to the MPL Low-Inertia Servo Motor Series within the MP-Series product family.
The MPL series uses permanent-magnet brushless servo technology and is designed for closed-loop industrial motion control.
The low-inertia construction is particularly useful when the motor must repeatedly accelerate and decelerate.
A conventional high-inertia motor stores more rotational energy in its rotor. A low-inertia servo motor can change rotational speed more rapidly when correctly matched to the load and servo drive.
This makes the MPL series suitable for applications where cycle time, positioning response, and coordinated motion are important.
6. Model Number Explanation
The model number MPL-B420P-HK74AA contains several configuration identifiers.
| Model Section | General Identification |
|---|---|
| MPL | MPL low-inertia servo motor family |
| B | B-series motor configuration |
| 4 | 115 mm frame class |
| 20 | 50.8 mm magnet-stack class |
| P | 5000 rpm performance class |
| H | Incremental encoder configuration |
| K | Keyless shaft |
| 7 | Circular SpeedTec DIN connector, right-angle, rotatable |
| 4 | Holding-brake configuration |
| AA | Product configuration designation |
The K designation is important because it identifies the motor as a keyless-shaft configuration.
The H feedback designation identifies the incremental encoder configuration.
The 4 in the brake/configuration section identifies the brake-equipped version.
Therefore, the HK74AA differs from the closely related HK72AA primarily in the inclusion of the integrated holding brake.
7. Motor Performance
The MPL-B420P-HK74AA provides a combination of high speed and relatively high torque within a compact low-inertia motor package.
The rated speed is 5000 rpm.
The continuous torque rating for the B420P class is approximately 4.74 N·m.
The peak torque capability is approximately 13.5 N·m.
The nominal power class is approximately 1.9 kW.
These characteristics make the motor suitable for machine axes that require rapid acceleration and deceleration rather than simple constant-speed operation.
8. Continuous Torque
The B420P motor class provides approximately 4.74 N·m continuous torque.
Continuous torque represents the torque that the motor can provide during sustained operation under the specified thermal and operating conditions.
For machine sizing, continuous torque should be compared with the RMS torque requirement of the complete motion profile.
A machine that repeatedly accelerates and decelerates should not be sized solely from its maximum instantaneous torque.
The designer should evaluate:
- Continuous load torque
- RMS torque
- Acceleration torque
- Deceleration torque
- Peak torque
- Duty cycle
- Motor speed
- Reflected inertia
- Ambient temperature
- Mechanical transmission efficiency
9. Peak Torque
The B420P class provides approximately 13.5 N·m peak torque.
Peak torque is useful during short-duration dynamic events such as:
- Rapid acceleration
- Rapid deceleration
- Indexing
- Direction reversal
- Load disturbance
- Short-duration overload
- High-speed positioning
The peak torque rating should not be treated as a continuous torque rating.
The actual available peak torque depends on the motor, servo drive, current capability, operating temperature, motion profile, and duration of the peak load.
10. Rated Speed
The MPL-B420P-HK74AA is rated for approximately 5000 rpm.
This high rotational speed is useful for machinery where a motor must operate at high speed while maintaining closed-loop control.
Typical examples include:
- High-speed indexing
- Roller drives
- Feed mechanisms
- Belt-driven axes
- Rotary positioning
- Packaging mechanisms
- Printing mechanisms
- High-speed material handling
The actual machine output speed will depend on the mechanical transmission ratio.
11. Power Rating
The B420P class has an approximate power rating of 1.9 kW.
Power alone should not be used as the only motor-selection criterion.
A servo motor must be selected according to the complete machine motion profile.
The following factors are important:
- Required torque
- Required speed
- Acceleration time
- Deceleration time
- Load inertia
- Transmission ratio
- Duty cycle
- RMS torque
- Peak torque
- Environmental conditions
- Servo drive compatibility
12. Low-Inertia Design
The low-inertia design is one of the main characteristics of the MPL series.
The B420P motor class has approximately 0.00026 kg·m² rotor inertia.
Low rotor inertia can be useful in machines that require frequent changes in speed.
When the motor accelerates, the drive must supply energy to accelerate the rotor and the reflected machine load.
When the motor decelerates, the rotational energy must be removed.
Reducing rotor inertia can therefore support rapid dynamic response when the motor is correctly sized and tuned.
This is particularly valuable in:
- Pick-and-place machines
- Packaging equipment
- Indexing systems
- Assembly machines
- Automated inspection systems
- High-speed transfer mechanisms
- Printing equipment
- Labeling equipment
13. Encoder Feedback
The MPL-B420P-HK74AA uses a 2000-line incremental encoder.
The encoder provides feedback to the servo drive for monitoring motor position and speed.
The incremental feedback arrangement is suitable for closed-loop servo applications where the drive and controller continuously use motor feedback.
Encoder feedback contributes to:
- Position control
- Velocity control
- Acceleration control
- Deceleration control
- Error detection
- Coordinated multi-axis operation
- Repeatable positioning
The encoder should be matched with the intended servo drive and control system.
14. Keyless Shaft
The HK74AA uses a keyless shaft.
This is one of the major mechanical characteristics distinguishing the HK74AA from keyed B420P configurations.
A keyless shaft can be used with suitable clamp-style couplings, hubs, or other compatible mechanical connections.
The coupling must be rated for the motor’s torque and speed.
The shaft configuration should always be verified before replacing a keyed motor with a keyless motor.
15. Integrated 24 V DC Holding Brake
One of the most important features of the HK74AA configuration is its 24 V DC holding brake.
The brake provides a mechanical holding function when the motor is not being actively driven.
This can be useful for applications where the motor axis needs to remain stationary after servo power is removed.
Typical examples include:
- Vertical positioning axes
- Elevators
- Lifting mechanisms
- Z-axis systems
- Material handling systems
- Vertical conveyors
- Automated positioning mechanisms
The brake should not automatically be treated as the primary safety device for every application.
Where a suspended load or hazardous movement is involved, the complete machine safety design must be evaluated separately.
16. HK74AA Versus HK72AA
The HK74AA and HK72AA are closely related B420P configurations.
| Feature | MPL-B420P-HK74AA | MPL-B420P-HK72AA |
|---|---|---|
| Motor Class | B420P | B420P |
| Frame | 115 mm | 115 mm |
| Stack | 50.8 mm | 50.8 mm |
| Rated Speed | 5000 rpm | 5000 rpm |
| Feedback | Incremental | Incremental |
| Encoder | 2000 lines/rev | 2000 lines/rev |
| Shaft | Keyless | Keyless |
| Shaft Seal | None | None |
| Brake | 24 V DC holding brake | No brake |
| Connector | SpeedTec DIN | SpeedTec DIN |
| Connector | Right-angle | Right-angle |
| Connector Rotation | 180° | 180° |
| Power Class | Approx. 1.9 kW | Approx. 1.9 kW |
| Continuous Torque | Approx. 4.74 N·m | Approx. 4.74 N·m |
| Peak Torque | Approx. 13.5 N·m | Approx. 13.5 N·m |
| Weight | Approx. 6.80 kg | Approx. 5.44 kg |
The main functional difference is the integrated holding brake.
The brake-equipped HK74AA is therefore particularly useful when the machine requires a motor holding function.
17. Applications
Packaging Machinery
The MPL-B420P-HK74AA can be used in automated packaging equipment requiring controlled rotary motion.
Typical applications include:
- Product indexing
- Film feeding
- Cutting mechanisms
- Sealing mechanisms
- Conveyor synchronization
- Product positioning
- Rotary packaging mechanisms
The low-inertia construction can support rapid cycle operation.
Pick-and-Place Systems
Pick-and-place machinery requires repeated acceleration, deceleration, and positioning.
The B420P motor’s 5000 rpm capability and low rotor inertia can be useful for fast axis movement.
The holding brake can also be valuable when an axis must remain mechanically held during power-off conditions, subject to the machine’s safety design.
Vertical Motion Systems
The integrated brake makes the HK74AA especially relevant to vertical axes.
Potential applications include:
- Z-axis mechanisms
- Vertical transfer units
- Lifting platforms
- Automated elevators
- Vertical indexing systems
- Material handling lifts
- Vertical positioning equipment
The brake function must be properly integrated with the drive and machine control system.
Assembly Machinery
Automated assembly equipment frequently uses servo motors for:
- Rotary positioning
- Insertion mechanisms
- Indexing
- Feeding
- Transfer
- Press mechanisms
- Screw-driving mechanisms
- Component positioning
The B420P torque and speed class provides a useful combination for these types of machines.
Material Handling Equipment
Servo-controlled material handling equipment can use the motor for:
- Roller drives
- Conveyor indexing
- Transfer mechanisms
- Positioning axes
- Lift axes
- Automated handling systems
The motor’s high-speed capability allows mechanical transmissions to be selected for higher motor operating speed where appropriate.
Printing and Labeling Machines
Printing and labeling machinery often requires synchronized motion between rollers, feeders, cutters, and other machine axes.
The incremental encoder provides the feedback required for closed-loop motor control.
The motor can therefore be considered for applications requiring repeatable speed and position control.
Automated Inspection Systems
Inspection machines frequently require fast movement between inspection positions.
The low-inertia design can support repeated rapid motion.
Typical examples include:
- Vision inspection systems
- Electronic component inspection
- Dimensional inspection
- Product sorting
- Automated testing equipment
18. Product Advantages
High-Speed Operation
The 5000 rpm rating provides high rotational speed for automated machinery.
This can allow the machine designer to use suitable gear ratios, belt ratios, pulleys, or other mechanical transmissions to achieve the required output speed.
Low-Inertia Response
The low-inertia design supports rapid changes in rotational speed.
This can be beneficial when machine cycle time depends on rapid acceleration and deceleration.
High Torque Density
The B420P class delivers approximately 4.74 N·m continuous torque and approximately 13.5 N·m peak torque.
This provides substantial torque capability within a 115 mm frame class.
Integrated Holding Brake
The HK74AA includes a 24 V DC holding brake.
This adds a mechanical holding function without requiring a separate external motor brake.
The brake can be particularly useful for vertical axes and applications where the motor must remain mechanically held when not energized.
Keyless Shaft
The keyless shaft provides compatibility with suitable clamp-style mechanical coupling systems.
This can simplify certain machine designs where a conventional keyed shaft is not preferred.
Incremental Encoder Feedback
The 2000-line incremental encoder provides closed-loop feedback for motion control.
This supports controlled speed and position operation when paired with a compatible servo drive.
Rotatable Connector
The right-angle SpeedTec DIN connector can be rotated through approximately 180 degrees.
This is useful for compact machines where cable routing space is limited.
Compact Mechanical Configuration
The 115 mm frame and 50.8 mm stack provide a compact motor configuration relative to its torque and speed class.
This can help reduce the space required for the servo axis.
19. Environmental and Operating Characteristics
The HK74AA is commonly specified with an IP20/NEMA 1 class configuration and an operating ambient range of approximately 0 to 40 °C.
| Environmental Parameter | Typical Specification |
|---|---|
| Model | MPL-B420P-HK74AA |
| Enclosure Classification | IP20 / NEMA 1 class |
| Operating Temperature | Approx. 0 to 40 °C |
| Storage Temperature | Application-dependent |
| Humidity | Approx. 5–95%, non-condensing |
| Maximum Altitude | Approx. 1000 m |
| Cooling | Motor-dependent / application installation |
| Shaft Seal | None |
| Intended Environment | Industrial indoor automation |
Actual installation conditions should be checked against the motor’s applicable technical documentation and the machine’s environmental requirements.
20. Mechanical Installation
Correct mechanical installation is important for servo motor performance.
The motor should be mounted on a rigid machine structure.
The shaft and driven load should be correctly aligned.
Improper alignment can result in:
- Excessive bearing loading
- Increased vibration
- Coupling wear
- Higher motor temperature
- Encoder errors
- Reduced service life
- Servo drive faults
The right-angle connector should also be positioned so that the motor cable does not experience excessive bending or mechanical stress.
21. Brake Installation Considerations
The integrated brake requires appropriate electrical control.
The 24 V DC brake circuit should be connected according to the applicable motor and servo-drive wiring requirements.
The brake should not be used as a dynamic stopping device unless the machine design specifically allows such operation.
A typical application uses the brake as a holding mechanism after the motor has stopped or when the servo system is disabled.
For vertical axes, brake timing should be coordinated with servo torque and machine movement to prevent unwanted load movement.
22. Servo Drive Compatibility
The MPL-B420P-HK74AA should be used with a compatible servo drive capable of supporting:
- The motor’s voltage class
- Required continuous current
- Required peak current
- Incremental encoder feedback
- 5000 rpm operation
- 24 V DC brake control
- Appropriate motor cable connections
Drive selection should also consider the machine’s regenerative energy requirements.
High-speed deceleration can return energy to the drive’s DC bus, and the complete system should be sized for the expected regenerative conditions.
23. Load Inertia Considerations
Servo motor selection requires more than matching power.
The reflected inertia of the machine load should be considered.
For example, a high-speed ball screw, pulley, gearbox, roller, or rotary table can present a substantially different inertia to the motor depending on the transmission ratio.
The B420P low-inertia rotor can provide good dynamic performance when appropriately matched with the reflected load.
Poor inertia matching can make servo tuning more difficult and may result in:
- Overshoot
- Oscillation
- Slower response
- Increased settling time
- Excessive motor current
- Positioning errors
24. Typical Industrial Applications
| Application | Typical Servo Function |
|---|---|
| Packaging Machine | Indexing and synchronization |
| Cartoning Machine | Product positioning |
| Labeling Machine | Feed and registration |
| Printing Machine | Roller synchronization |
| Pick-and-Place | High-speed positioning |
| Assembly Machine | Rotary indexing |
| Inspection Equipment | Rapid positioning |
| Conveyor System | Servo indexing |
| Material Handling | Positioning and lifting |
| Vertical Axis | Positioning with brake holding |
| Rotary Table | Indexing |
| Feeding System | Controlled feed motion |
| Cutting Machine | Synchronization and positioning |
| Automated Transfer | Rapid axis movement |
| Production Line | Coordinated multi-axis motion |
25. Five Related or Same-Series Models
The following models are closely related to the MPL-B420P-HK74AA.
| Model | Frame | Stack | Speed | Feedback | Shaft | Brake | Power Class | Approx. Weight |
|---|---|---|---|---|---|---|---|---|
| MPL-B420P-HK72AA | 115 mm | 50.8 mm | 5000 rpm | 2000-line incremental | Keyless | No | 1.9 kW | Approx. 5.44 kg |
| MPL-B420P-HJ72AA | 115 mm | 50.8 mm | 5000 rpm | 2000-line incremental | Keyed | No | 1.9 kW | Configuration-dependent |
| MPL-B420P-HJ74AA | 115 mm | 50.8 mm | 5000 rpm | 2000-line incremental | Keyed | 24 V DC | 1.9 kW | Approx. 7.29 kg |
| MPL-B420P-MK72AA | 115 mm | 50.8 mm | 5000 rpm | Multi-turn absolute | Keyless | No | 1.9 kW | Configuration-dependent |
| MPL-B420P-SJ72AA | 115 mm | 50.8 mm | 5000 rpm | Single-turn absolute | Keyed | No | 1.9 kW | Configuration-dependent |
These models are useful comparison points because they share the B420P motor class while providing different feedback, shaft, and brake configurations.
26. B420P Configuration Comparison
| Model | Feedback | Shaft | Brake | Main Configuration |
|---|---|---|---|---|
| MPL-B420P-HK72AA | Incremental | Keyless | No | Keyless, no-brake |
| MPL-B420P-HK74AA | Incremental | Keyless | 24 V DC | Keyless, brake |
| MPL-B420P-HJ72AA | Incremental | Keyed | No | Keyed, no-brake |
| MPL-B420P-HJ74AA | Incremental | Keyed | 24 V DC | Keyed, brake |
| MPL-B420P-MK72AA | Multi-turn absolute | Keyless | No | Absolute feedback |
| MPL-B420P-MJ72AA | Multi-turn absolute | Keyed | No | Absolute + keyed |
| MPL-B420P-MJ74AA | Multi-turn absolute | Keyed | 24 V DC | Absolute + brake |
| MPL-B420P-SJ72AA | Single-turn absolute | Keyed | No | Single-turn + keyed |
| MPL-B420P-SJ74AA | Single-turn absolute | Keyed | 24 V DC | Single-turn + brake |
The B420P family contains numerous combinations of feedback and mechanical configuration, making it important to compare the complete model number rather than selecting a motor based only on frame size and power.
27. Five Representative Same-Brand Models
The following five models provide a useful performance comparison within the same MPL family.
| Model | Speed | Continuous Torque | Peak Torque | Power | Rotor Inertia | Weight | Frame / Size Reference |
|---|---|---|---|---|---|---|---|
| MPL-B310P | 5000 rpm | 1.58 N·m | 3.61 N·m | 0.77 kW | 0.000044 kg·m² | 2.7 kg | Smaller frame class |
| MPL-B320P | 5000 rpm | 3.05 N·m | 7.91 N·m | 1.5 kW | 0.000078 kg·m² | 3.7 kg | Smaller frame class |
| MPL-B330P | 5000 rpm | 4.18 N·m | 11.1 N·m | 1.8 kW | 0.00012 kg·m² | 4.6 kg | Smaller frame class |
| 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 | 115 mm class |
| MPL-B430P | 5000 rpm | 6.55 N·m | 19.8 N·m | 2.2 kW | 0.00038 kg·m² | 5.5 kg | Larger performance class |
These models represent a useful progression in the MPL low-inertia servo motor range.
The B310P is a lower-power option, while the B320P and B330P provide progressively higher torque.
The B420P increases the torque and power level further, while the B430P provides an even higher torque class.
28. Same-Series Performance Comparison
| Model | Rated Speed | Continuous Torque | Peak Torque | Power |
|---|---|---|---|---|
| MPL-B310P | 5000 rpm | 1.58 N·m | 3.61 N·m | 0.77 kW |
| MPL-B320P | 5000 rpm | 3.05 N·m | 7.91 N·m | 1.5 kW |
| MPL-B330P | 5000 rpm | 4.18 N·m | 11.1 N·m | 1.8 kW |
| MPL-B420P | 5000 rpm | 4.74 N·m | 13.5 N·m | 1.9 kW |
| MPL-B430P | 5000 rpm | 6.55 N·m | 19.8 N·m | 2.2 kW |
This progression can be useful when comparing the B420P against smaller or larger MPL motor classes.
The B420P provides a balance between the B330P and B430P performance levels.
29. Five Related Models – Detailed Reference
MPL-B420P-HK72AA
The HK72AA is the closest mechanical and electrical comparison to the HK74AA.
It uses the same B420P performance class, 115 mm frame, 50.8 mm stack, 5000 rpm speed class, keyless shaft, and incremental feedback arrangement.
The primary difference is the absence of the integrated holding brake.
Approximate weight is 5.44 kg.
MPL-B420P-HJ72AA
The HJ72AA uses a keyed shaft instead of the keyless shaft used by the HK74AA.
This model can therefore be considered when the machine uses conventional keyed couplings.
It retains the general B420P performance class and incremental feedback arrangement.
MPL-B420P-HJ74AA
The HJ74AA combines a keyed shaft with a 24 V DC holding brake.
It can be considered where both a conventional keyed shaft and an integrated holding brake are required.
The model remains within the same B420P motor performance class.
MPL-B420P-MK72AA
The MK72AA uses a keyless shaft and a multi-turn absolute feedback arrangement.
This makes it a relevant comparison where the control architecture requires absolute multi-turn position information rather than conventional incremental feedback.
MPL-B420P-SJ72AA
The SJ72AA uses single-turn absolute feedback and a keyed shaft.
It can be considered when the machine requires a different feedback architecture and a conventional keyed shaft connection.
30. Application Selection Table
| Machine Requirement | Relevant Model |
|---|---|
| Keyless shaft + incremental encoder + brake | MPL-B420P-HK74AA |
| Keyless shaft + incremental encoder + no brake | MPL-B420P-HK72AA |
| Keyed shaft + incremental encoder + no brake | MPL-B420P-HJ72AA |
| Keyed shaft + incremental encoder + brake | MPL-B420P-HJ74AA |
| Keyless shaft + multi-turn feedback | MPL-B420P-MK72AA |
| Keyed shaft + multi-turn feedback | MPL-B420P-MJ72AA |
| Keyed shaft + single-turn feedback | MPL-B420P-SJ72AA |
| Higher torque than B420P | MPL-B430P |
| Lower torque requirement | MPL-B330P / B320P |
31. Advantages for Vertical Applications
The integrated brake is particularly relevant when the servo motor operates a vertical axis.
A vertical load can move due to gravity when motor torque is removed.
The holding brake can provide a mechanical holding function when the servo axis is stopped, provided that the brake is correctly sized and applied within its specified operating conditions.
Potential applications include:
- Vertical transfer units
- Z-axis positioning systems
- Lifting equipment
- Automated storage machinery
- Vertical conveyors
- Robotic vertical axes
- Machine-tool vertical axes
The complete machine safety system should always provide appropriate protection for suspended or hazardous loads.
32. Advantages for High-Speed Automation
The 5000 rpm rating allows the motor to operate at high speed.
The low-inertia rotor supports rapid changes in motor speed.
The incremental encoder provides feedback for closed-loop control.
The 24 V DC brake provides an additional holding function.
The keyless shaft supports compatible high-speed coupling systems.
The rotatable right-angle connector simplifies cable routing.
Together, these characteristics make the HK74AA suitable for a wide range of high-speed industrial automation systems.
33. Maintenance Considerations
The motor itself generally requires limited routine mechanical maintenance, but the complete servo system should be inspected periodically.
Important inspection points include:
- Motor mounting bolts
- Shaft coupling
- Cable condition
- Connector condition
- Brake operation
- Encoder feedback
- Motor temperature
- Vibration
- Bearing noise
- Machine alignment
- Cable routing
- Environmental contamination
Because the motor has no shaft seal, the machine environment around the shaft should be considered carefully.
The brake should also be checked for correct release and holding operation where the application depends on the brake.
34. Replacement Considerations
When replacing another servo motor with the MPL-B420P-HK74AA, the following specifications should be compared:
- Motor voltage class
- Rated speed
- Continuous torque
- Peak torque
- Frame size
- Magnet stack length
- Shaft type
- Shaft dimensions
- Feedback type
- Encoder resolution
- Brake availability
- Connector type
- Connector orientation
- Mounting flange
- Overall motor envelope
- Cable compatibility
- Drive compatibility
- Load inertia
- Machine duty cycle
- Environmental requirements
A motor with similar power but different feedback, shaft, brake, or connector configuration may not be a direct replacement.
35. Technical Specification Summary
| Category | Specification |
|---|---|
| Model | MPL-B420P-HK74AA |
| Brand | Allen-Bradley |
| Family | MP-Series |
| Series | MPL Low-Inertia Servo Motors |
| Motor Type | Permanent-Magnet Brushless AC Servo |
| Voltage Class | 460/480 V AC |
| Rated Speed | 5000 rpm |
| Continuous Torque | Approx. 4.74 N·m |
| Peak Torque | Approx. 13.5 N·m |
| Power Class | Approx. 1.9 kW |
| Frame Size | 115 mm |
| Magnet Stack | 50.8 mm |
| Feedback | 2000-line incremental encoder |
| Shaft | Keyless |
| Shaft Seal | None |
| Brake | 24 V DC holding brake |
| Connector | Circular SpeedTec DIN |
| Connector Type | Right-angle |
| Connector Rotation | 180° |
| Mounting | IEC Metric |
| Mounting Holes | Free mounting holes / Type FF |
| Rotor Inertia | Approx. 0.00026 kg·m² |
| Enclosure Class | IP20 / NEMA 1 class |
| Operating Temperature | Approx. 0 to 40 °C |
| Humidity | Approx. 5–95%, non-condensing |
| Altitude | Approx. 1000 m |
| Weight | Approx. 6.80 kg |
| Overall Dimensions | Configuration-dependent |
| Primary Use | Industrial motion control |
| Typical Applications | Packaging, indexing, assembly, material handling, vertical axes, positioning |
36. Complete Product Description
The Allen-Bradley MPL-B420P-HK74AA is a 5000 rpm, low-inertia permanent-magnet AC servo motor designed for demanding industrial motion-control applications.
The motor belongs to the MPL Low-Inertia Servo Motor Series and uses a 115 mm frame with a 50.8 mm magnet stack.
Its B420P performance class provides 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 motion feedback.
Its keyless shaft is suitable for compatible mechanical coupling systems, while the 24 V DC holding brake provides a useful holding function for applications where the motor must remain stationary after active servo operation.
The right-angle circular SpeedTec DIN connector can be rotated through approximately 180 degrees, providing flexibility when the motor is installed in a compact automation machine.
The low-inertia construction is particularly suitable for applications that require repeated acceleration and deceleration.
Typical applications include packaging equipment, indexing machines, pick-and-place systems, assembly equipment, material handling systems, printing machinery, labeling machines, automated inspection equipment, rotary positioning systems, and vertical servo axes.
For vertical or gravity-loaded applications, the integrated brake is an important functional advantage, although the complete machine safety system must determine whether additional mechanical holding or safety provisions are required.
The keyless shaft also differentiates the HK74AA from keyed B420P configurations such as the HJ-series models.
When selecting a replacement or equivalent motor, the complete configuration should be considered rather than comparing only nominal power.
The feedback type, encoder resolution, shaft configuration, brake, connector, frame size, stack length, mounting pattern, motor envelope, cable system, and servo-drive compatibility should all match the requirements of the machine.
37. Final Specification at a Glance
| Item | Final Specification |
|---|---|
| Model | MPL-B420P-HK74AA |
| Brand | Allen-Bradley |
| Series | MPL Low-Inertia Servo Motors |
| Family | MP-Series |
| Motor Type | Brushless Permanent-Magnet AC Servo Motor |
| Voltage | 460/480 V AC class |
| Rated Speed | 5000 rpm |
| Continuous Torque | 4.74 N·m |
| Peak Torque | Approx. 13.5 N·m |
| Power | Approx. 1.9 kW |
| Frame Size | 115 mm |
| Stack Length | 50.8 mm |
| Encoder | 2000-line incremental |
| Shaft | Keyless |
| Shaft Seal | None |
| Brake | 24 V DC Holding Brake |
| Connector | Circular SpeedTec DIN |
| Connector Position | Right-angle |
| Connector Rotation | 180° |
| Mounting | IEC Metric, Type FF |
| Rotor Inertia | Approx. 0.00026 kg·m² |
| Approximate Weight | 6.80 kg |
| Typical Environment | Industrial indoor automation |
| Typical Applications | Packaging, indexing, assembly, positioning, material handling, vertical axes |
| Main Characteristics | High speed, low inertia, incremental feedback, keyless shaft, integrated holding brake |
The MPL-B420P-HK74AA is therefore a high-speed, low-inertia, 1.9 kW-class servo motor with 5000 rpm operation, 4.74 N·m continuous torque, approximately 13.5 N·m peak torque, 2000-line incremental feedback, a keyless shaft, and an integrated 24 V DC holding brake.