Harmonic Drive HMA Hollow-Shaft Servo Motors Review: Specs, Price and Applications
Updated: 4 days ago
Harmonic Drive HMA is a family of hollow-shaft AC servo motors with absolute feedback and an optional brake. Five frame sizes cover rated outputs from 163 to 1320 W, with a central passage for cables, shafts or optical paths through the motor axis.
Quick Verdict
HMA is a candidate when a through-axis passage and a flat motor arrangement solve a real packaging problem. Match the winding, encoder and brake configuration to the chosen amplifier, and design the thermal mounting around the manufacturer's rating conditions. Neither the family power maximum nor the encoder count establishes complete machine performance.
Harmonic Drive HMA Hollow-Shaft Servo Motors at a Glance
Specification | Details |
Motor family | HMA; five frame sizes with multiple ordering configurations |
HMAC08 rated operating point | 0.52 Nm; 3000 rpm; 163 W |
HMAB09 rated operating point | 0.80 Nm; 3000 rpm; 251 W; distinct winding choices |
HMAB12 rated operating point | 1.55 Nm; 2500 rpm; 406 W |
HMAB15 rated operating point | 3.6 Nm; 2000 rpm; 754 W |
HMAA21 rated operating point | 12.6 Nm; 1000 rpm; 1320 W |
Feedback | 17-bit single-turn absolute encoder; 16-bit battery-buffered multi-turn counter |
Brake option | With or without brake; configuration dependent |
Rating conditions | Typical values; manufacturer specifies HA-800 test conditions and frame-specific aluminum heatsinks |
Design and Engineering Assessment
The opening through the motor can simplify an otherwise awkward mechanical layout. It may allow a machine service or optical path to remain near the rotation axis instead of following an external loop. That benefit should be checked against the actual usable bore and connector clearances in the dimension drawing, not assumed from the family name.
The rated operating points belong to different models. HMAA21's 1320 W is paired with 12.6 Nm at 1000 rpm, whereas HMAC08's 163 W is paired with 0.52 Nm at 3000 rpm. Combining the largest torque with the smallest motor's speed would describe a configuration that is not established by this data.
The manufacturer conditions the thermal ratings on specified aluminum heatsinks after temperature rise has stabilized. For example, the HMAC08 reference is 320 × 320 × 16 mm, while HMAA21A uses 650 × 650 × 30 mm. A small mounting bracket should not be assumed to reproduce those thermal conditions.
The 17-bit single-turn encoder provides 131072 nominal counts per motor revolution. It does not establish the accuracy of a machine output or the stiffness of its load path. Mounting error, feedback alignment, compliance and any reduction remain part of the complete positioning budget.
Servo Drive and Winding Compatibility
The manufacturer's page identifies interfaces to particular Mitsubishi MELSERVO-J4, Yaskawa Sigma-7 and Panasonic MINAS A5II/A5IIN arrangements through the relevant manuals. Compatibility is an ordering and wiring matter, not a promise that any HMA can be plugged into every drive bearing one of those family names.
The HMAB09 appears with different winding configurations. Select the precise voltage class and current requirements with the amplifier documentation, including feedback and cable details. Do not treat different mains-side drive supply labels and motor winding designations as interchangeable specifications.
Thermal Design and Duty
Calculate the sustained load and acceleration duty together with available heat transfer through the motor mount. The reference heatsink dimensions show why continuous output depends on the surrounding structure. Confirm performance in the actual enclosure and ambient conditions rather than selecting from a peak-torque headline.
Motor peak torque is useful for transient demand, but repeated accelerations can still generate excessive heat. Include current limits, regeneration and the amplifier's own duty restrictions in the same calculation. A motor and an amplifier must both support the proposed cycle.
Brake and Multi-Turn Feedback
The optional brake changes the selected motor's mass and inertia. Treat it as a specified mechanical function with its own control and holding requirements. It must not be assumed to provide emergency stopping or a certified machine-safety function without the relevant documentation.
The multi-turn count is battery buffered. Define the maintenance and recovery procedure for the exact system, including what happens after battery loss or replacement. Remembering a motor revolution count is different from proving that the complete machine retains its calibrated work coordinate.
Mechanical Integration and Alternatives
Check allowable shaft loads, mounting geometry and the load's own bearing arrangement before applying force through the motor. A hollow-shaft motor can still require separate load support. Cable or optical routing through the center must remain clear throughout the intended motion and maintenance access.
Compare HMA with an ordinary motor plus an offset transmission, a hollow-shaft gear unit or a complete geared actuator using the same output duty. The appropriate choice depends on speed, torque, passage size, thermal mounting and serviceability. A motor family should not be compared with a complete actuator as if both include identical hardware.
HMA Servo Motors Versus KDU Direct-Drive Rotary Axes
The broader hollow-shaft motor portfolio also includes KDU direct-drive rotary motors. HMA supplies a hollow-shaft servo motor that the machine designer integrates with its chosen transmission or direct mechanical load. KDU is a separate direct-drive positioning family with a matched-drive and correction-data scope. Do not apply KDU positioning figures to an arbitrary HMA motor or assume that sharing a manufacturer and central passage makes the two constructions interchangeable.
The KDU documentation identifies HA-770-2 as the matched drive and quotes 10 arcsec corrected positioning accuracy and ±0.5 arcsec repeatability under specified conditions: 23 ±0.3°C, 50% relative humidity and output shaft facing upward. Those figures depend on the documented motor/drive/correction arrangement and test conditions. They are not an uncontrolled shop-floor guarantee, an HMA specification or a promise for every load orientation.
Choose HMA by its exact winding, torque-speed duty, encoder, brake and mechanical load requirements. Choose a KDU arrangement by the complete direct-drive positioning duty, bearing loads, correction procedure and thermal conditions. For either route, compare the installed support structure, cabling, control and load-point acceptance criteria rather than only motor power or a fine encoder increment.
Applications and Selection
Rotary mechanisms requiring a motor-axis passage for cables, shafts or an optical path, with the load and any reduction selected around the exact motor operating point.
For Harmonic Drive HMA Hollow-Shaft Servo Motors, define the actual machine duty before selecting an ordering configuration. Include the required operating point, available installation space, environment and control interfaces. The specification table describes the product or family; the surrounding machine determines which of those features matters for the intended job.
Price and Value
Price: Request a quote for the exact configuration. Compare the product, compatible control equipment, required mechanical parts, cabling and commissioning as one installed system. A component price alone does not represent the cost of a working automation axis.
Evaluate an alternative against the same duty and acceptance criteria. Match the continuous operating requirement first, then compare transient capability, feedback, mechanical fit and support. This avoids choosing between superficially similar products whose ratings describe different operating conditions.
Pros and Cons
Advantages
Through-axis passage can simplify service or optical routing
Five frame sizes offer distinct torque-speed operating points
Absolute single-turn and battery-buffered multi-turn feedback
Optional brake and documented drive-specific arrangements
Limitations
External compatible amplifier and configuration-specific cabling required
Continuous ratings depend on defined thermal mounting conditions
Encoder resolution does not establish machine accuracy
Brake and multi-turn functions add integration and maintenance requirements
Who Should Consider Harmonic Drive HMA Hollow-Shaft Servo Motors?
Consider Harmonic Drive HMA Hollow-Shaft Servo Motors for rotary mechanisms requiring a motor-axis passage for cables, shafts or an optical path, with the load and any reduction selected around the exact motor operating point. Establish the required operating point and installation interfaces before choosing the configuration, and use a representative loaded cycle as the acceptance basis.
Harmonic Drive HMA Hollow-Shaft Servo Motors FAQ
What is the HMA hollow-shaft servo motor?
HMA is an AC servo-motor family with a central opening, absolute feedback and an optional brake. It provides motor torque and motion; it is not automatically a complete geared actuator with a servo amplifier.
What power range does the family cover?
The published rated outputs extend from 163 W to 1320 W across five frame sizes. Each model has its own rated torque and speed. The largest power value must not be combined with another model's operating speed.
Is the encoder 17-bit or 16-bit?
The published single-turn absolute resolution is 17 bits, or 131072 counts per motor revolution. The separate battery-buffered multi-turn counter is 16-bit. These describe different feedback functions.
Which servo drives can be used?
The manufacturer identifies specific Mitsubishi MELSERVO-J4, Yaskawa Sigma-7 and Panasonic MINAS A5II/A5IIN arrangements through supporting manuals. Confirm the exact motor code, winding, encoder interface, drive configuration and cables before ordering.
Can the rated torque be used on any small mounting plate?
The manufacturer specifies frame-dependent aluminum heatsinks for the stabilized thermal ratings. A smaller or poorly conducting mount may not reproduce those conditions. Evaluate the actual thermal path and loaded duty before accepting the continuous requirement.
Does the optional brake provide a safety stop?
Do not assume that. Specify the required holding behavior and check the brake documentation, control sequence and machine-safety design. A brake option alone is not evidence of an independently certified safety function.
What does an HMA motor cost?
Request a quote for the exact frame, winding, encoder, brake, cables and amplifier arrangement. There is no verified universal family price here, and motor-only cost does not represent the complete installed axis.
What should commissioning verify?
Verify motor and feedback wiring, direction, current limits, brake sequence and the handling of multi-turn position. Test the intended loaded duty and thermal behavior, and verify the actual output position against the machine's required acceptance criteria.
Prices are indicative and may change. Confirm the final configuration, commercial terms and delivery schedule before ordering.
