AC Servo Drive + Motor System (100W–7.5kW OEM)

Encoder Resolution: What 17-bit vs 23-bit Actually Buys You

Chinese AC servo manufacturers now ship three encoder tiers across most product lines: 17-bit (131,072 PPR), 20-bit (1,048,576 PPR), and 23-bit (8,388,608 PPR) absolute encoders. The resolution numbers are real. The positioning improvement they deliver at the workpiece frequently is not — because encoder resolution is rarely the binding constraint.

Where resolution matters. A 17-bit single-turn encoder on an 80mm-frame motor with a 5mm ball-screw pitch gives a minimum step of 5mm ÷ 131,072 ≈ 38nm. A 23-bit encoder gives 0.6nm. In most machine-tool applications, the actual positioning repeatability at the workpiece is limited by ball-screw backlash (2–15μm for a new C5-grade screw), thermal expansion of the screw under continuous duty (10–20μm per 10°C rise over 1m of screw), and compliance in the coupling between motor shaft and screw. Encoder resolution is not the constraint.

Where resolution does not matter. For standard CNC, pick-and-place, and general servo press applications, 17-bit is sufficient. Specifying 23-bit for a 5mm pitch ball-screw in a standard milling machine costs more and provides no measurable benefit. Inovance, ESTUN, and Huichuan all offer 17-bit encoder variants at 15–25% lower cost than their 20-bit equivalents. For most industrial IoT machine builders, this is the correct choice.

Single-turn vs multi-turn absolute. Single-turn absolute encoders retain position within one revolution on power loss; multi-turn absolute encoders (battery-free magnetic variants are now standard in Chinese tier-1 suppliers) retain position across up to 65,536 full revolutions without a homing cycle. For any axis that could be moved manually with the machine off — a gantry axis, a rotary table, a robot joint — specify multi-turn absolute. The cost premium over single-turn is typically $15–35 per motor at the unit prices relevant to sourcing from China. Eliminating the homing cycle pays back immediately in machine uptime.

Bus Protocol Selection: Pulse+Dir, CANopen, or EtherCAT

Four fieldbus interfaces are available from Chinese servo manufacturers. The choice depends on axis count, synchronization requirements, and whether you are integrating with an existing motion controller or selecting a new one.

Pulse+Direction (Pulse+Dir). Universal input accepted by every servo drive made in China. A 500kHz pulse output from any PLC or dedicated motion controller gives a minimum command step of 1 encoder count. Simple, debuggable with an oscilloscope, and not subject to licensing. The limitation is latency: each axis receives independent position commands with no hardware synchronization mechanism. For single-axis applications, or multi-axis applications where axis synchronization is handled by the host controller with position-matched profiles, Pulse+Dir is adequate. For high-speed coordinated motion (electronic cam, flying shear, high-speed packaging) it is not — the inter-axis jitter from separate pulse trains causes synchronization errors at the workpiece.

CANopen (DS402 profile). 1Mbps bus, typically supports 16–32 nodes. Cycle time 2–10ms in practice. Adequate for most CNC machine tool applications (3–6 axes, contouring at <5m/min). Chinese manufacturers including Delta Electronics and lower-tier brands support CANopen DS402 natively in their mid-range drives. The limitation at higher axis counts is bus utilization: at 1Mbps with 8-byte PDO messages, 16 axes at 2ms cycle time consumes approximately 80% of bus bandwidth, leaving no headroom for SDO parameter writes or error handling. Do not plan a 20-axis CANopen system without bus utilization analysis.

EtherCAT (CoE — CAN over EtherCAT, IEC 61800-7-201). 100Mbps, cycle time <100μs achievable, supports 100+ axes in a single network. Required for collaborative robots, high-speed packaging (300+ packs/min), and any application specifying real-time multi-axis synchronization. Inovance (SV660N series) and ESTUN (ProNet-E series) both support EtherCAT natively. Critical licensing note: EtherCAT is an open standard (IEC 61158-12), but the EtherCAT Technology Group (ETG) membership and ASIC sourcing from Beckhoff (ET1100, ET1200) are the practical implementation paths. Chinese tier-1 manufacturers use licensed EtherCAT ASICs — verify ETG membership before accepting an “EtherCAT-compatible” drive from an unknown brand. A drive with a cloned EtherCAT implementation will pass basic connectivity but fail the distributed clock synchronization required for sub-100μs jitter.

MECHATROLINK-III. Proprietary to Yaskawa; 100Mbps, 31.25μs cycle time. Relevant only if integrating with a Yaskawa motion controller. Chinese drives supporting MECHATROLINK-III require a consortium license; Inovance offers it in their SV660-series under a licensing agreement. Do not specify MECHATROLINK-III for new designs unless you are locked into an existing Yaskawa controller architecture.

Our sourcing service pre-qualifies servo suppliers against their declared fieldbus implementation — including ETG membership verification for EtherCAT claims — before recommending a shortlist.

Motor Frame Size, Mounting Interface, and Environmental Options

Chinese AC servo motors are built to GB/T 22670 (equivalent to IEC 60072-1 for flange mounting dimensions). The five standard flange sizes — 60mm, 80mm, 100mm, 130mm, 180mm — share mounting bolt pattern, pilot diameter, and shaft diameter with IEC 60072-1 equivalents, with minor exceptions at 40mm (a Chinese-specific small-frame size not present in IEC 60072-1). NEMA frame sizes are not directly compatible: a NEMA 34 motor is not a drop-in replacement for a 130mm-flange Chinese servo motor without an adapter plate.

Frame size and continuous torque. Continuous torque scales approximately with rotor volume, which scales with frame size cubed. A 60mm-frame motor tops out at approximately 0.64 N·m continuous at 3,000 RPM (200W), while a 130mm-frame motor delivers 7.7 N·m continuous at 2,000 RPM (1.6kW). Do not attempt to close the gap by running a small-frame motor at peak torque continuously — peak torque is rated for duty cycles <10% of operating time. Thermal saturation of a 60mm motor at 150% rated torque for 30 seconds will be visible on a thermal camera during factory inspection.

Electromagnetic brake option. Chinese servo motors are available with an integrated fail-safe electromagnetic brake (power-off engage, 24V DC release). The brake holds the axis stationary on E-stop and power loss — required for vertical axes (Z-axes in gantries, robot joints). Brake holding torque is typically 1.5–2× rated motor torque. Verify that the brake is specified as a holding brake, not a dynamic brake: most integrated servo brakes are not rated for repeated engagement at speed and will fail within thousands of cycles if used that way. Dynamic stopping must still be achieved by the drive’s regenerative braking; the mechanical brake engages only after the axis has reached near-zero velocity.

Shaft seal and IP rating. Standard Chinese servo motors are IP65 — dust-tight and protected against water jets from any direction (IEC 60529). IP67 (immersion to 1m for 30 minutes) is available from tier-1 manufacturers and is required for applications with coolant flooding or wash-down. The shaft seal is the weakest point: a standard labyrinth seal is adequate for IP65 but not IP67. Verify that the motor datasheet explicitly states IP67 for the shaft seal, not just for the motor body. For coolant-exposure applications, confirm the shaft seal material (PTFE is superior to NBR for cutting fluid resistance).

Winding insulation class. Class F (155°C maximum winding temperature) is standard. At 100% continuous torque and 40°C ambient, a well-designed Class F motor runs with 30–40°C thermal margin. Class H (180°C maximum) is worth specifying for high-ambient environments (>50°C enclosure temperature) or applications with frequent short-duration overloads. The cost premium is typically <8% at the motor level.

Chinese Servo Supplier Landscape and Performance Verification

Four manufacturers dominate the Chinese AC servo market for OEM machine builders. Understanding their tier positioning is necessary for selecting the right supplier for a given application.

Inovance (汇川技术, Shenzhen). The largest Chinese servo manufacturer by installed base. Their SV660N (EtherCAT) and MD810 series are the reference products for Chinese-made AC servo. Performance specs are credible and verifiable: 2,500Hz velocity bandwidth at rated inertia, 17-bit or 23-bit absolute encoder options, full EtherCAT CoE support with distributed clock synchronization. Inovance is ETG member number 3058 — confirmed. Lead times from stock typically 5–10 days. Price premium of 20–35% over budget-tier brands is justified for applications requiring verified EtherCAT performance or CE + UL 508 dual certification.

ESTUN (埃斯顿, Nanjing). Strong in robotics and packaging OEM. The ProNet-E series (EtherCAT) is their flagship for multi-axis coordinated motion. ESTUN manufactures both the drive and motor in-house, which simplifies matched impedance optimization across the drive-motor-cable system. Their documentation quality is notably higher than most Chinese servo brands — English manuals are maintained with current firmware versions.

Huichuan (汇川, Shenzhen). Note: Huichuan and Inovance are different companies despite similar romanization. Huichuan’s IS620N series covers 200W–7.5kW and targets cost-sensitive OEM machine builders. Performance is adequate for standard CNC and conveyor applications; EtherCAT implementation should be verified against real distributed clock tests before committing to multi-axis synchronized applications.

Delta Electronics (台达, Taiwan, manufactured in Wujiang). Delta’s ASDA-A3 and ASDA-B3 series are manufactured in mainland China and are available through Chinese distribution. Performance is tier-1, documentation is excellent, and CE + UL 508 dual certification is standard. Lead times can be longer than pure mainland alternatives due to cross-strait supply chain coordination.

Performance verification during audit. During our factory audit of servo suppliers, we verify three parameters that distinguish genuine tier-1 performance from paper specifications:

1. Velocity bandwidth at rated inertia ratio. Inject a sinusoidal velocity reference sweep from 1Hz to 3,000Hz and measure the -3dB frequency with the motor connected to a load inertia at the manufacturer’s rated ratio (typically 3:1). A genuine 2,500Hz bandwidth servo will measure 2,300–2,700Hz; a budget drive claiming 2,500Hz often breaks below 800Hz at rated inertia.

2. Position repeatability. Command 1,000 consecutive ±5mm moves on a ballscrew test fixture and measure repeatability with a laser interferometer. For a 17-bit encoder, ±1 encoder count corresponds to approximately ±30 arcseconds (≈±4μm at 5mm pitch). Real-world repeatability in a well-assembled fixture should be ±1–2μm at 20°C. Document the result — this is the number your machine builder customers need.

3. Thermal rise at 100% continuous torque. Run the motor at rated torque and rated speed for 2 hours and measure winding temperature by resistance method (R hot/R cold ratio). Class F winding should not exceed 115°C rise over 40°C ambient (155°C total). A motor running at 145°C winding temperature at rated load has no thermal margin for real applications. This test eliminates suppliers who overstate their motor’s continuous torque rating by 15–25%.

For a real example of multi-axis servo drive integration in an industrial automation project, see the EU industrial IoT gateway case study. For sourcing with matched drive-motor-cable assemblies from a verified Chinese supplier, contact us via our sourcing service.