ETEL IL+/LM Linear Motor Selection and Integration Guide

Complete Guide to Selection and Integrated Application of ETEL IL+/LM Series Linear Motor Technology

In the field of precision motion control, linear motors are gradually replacing the traditional "rotary motor+screw/belt" transmission scheme, becoming the preferred power source for high acceleration, high precision, and long-life applications. As a pioneer in direct drive technology, ETEL has been focusing on the research and development of linear motors and torque motors since 1994. Its IL+(ironless) and LM (iron core) series cover a wide range of applications from nanoscale positioning to high-density heavy-duty drives. However, faced with a plethora of model parameters such as sustained force, peak force, magnetic pole period, heat dissipation method, voltage level, etc., engineers often find it difficult to quickly identify the most suitable model for specific application scenarios. This article combines the core selection framework of the ETEL IL+/LM series product manual, systematically sorts out the differences and selection points between the two technologies, and provides integrated debugging suggestions with the ETEL DSC series servo controller.

Core advantages of direct drive technology

Before delving into the selection process, it is necessary to clarify the fundamental changes brought about by "direct drive". In traditional transmission chains, motors convert rotational motion into linear motion through screws, belts, or gears. These intermediate links introduce problems such as elastic deformation, backlash, friction, and inertia matching, which limit the system bandwidth and positioning accuracy. Direct drive couples the load directly with the motor rotor, eliminating all mechanical transmission components. Its advantages include:

Zero backlash: There is no backlash of the screw nut or gear, and the repeatability of positioning is significantly improved.

High stiffness: The air gap between the rotor and stator forms an "air cushion spring", and the electrical stiffness is much higher than that of the mechanical transmission chain.

High acceleration: The load is directly subjected to force, without the need to overcome the inertia and friction of transmission components, and can achieve acceleration of tens of grams.

Maintenance free: No wear parts (such as screws and belts), with an extremely long lifespan in clean environments or high demand industrial applications.

Simplify mechanical design: reduce the number of parts, lower the overall size and weight of the machine.

ETEL's linear motor products are based on the above concept and have been widely used in fields such as semiconductor manufacturing, flat panel display inspection, laser processing, precision measurement, and biomedicine.

Two major technological routes: IL+(coreless) vs LM (coreless)

The ETEL linear motor product line is divided into two major camps, with the core difference being whether the actuator uses ferromagnetic materials as the magnetic circuit.

2.1 LM Series - Iron Core Linear Motor

The rotor of the iron core motor is made of stacked silicon steel sheets, and the winding is embedded in the slot, which interacts with the permanent magnet stator (magnetic track) to generate thrust.

Core advantages:

High force density: The thrust generated per unit volume or unit current is much higher than that of ironless motors. The LM series includes sub series such as LMS (standard force density) and LMG (high force density), with a maximum continuous thrust of several thousand newtons.

High voltage compatibility: Supports bus voltages up to 340Vdc (or even higher), matched with the high-voltage version of the ETEL DSC series controllers, suitable for heavy-duty and high-speed applications.

Extremely low force ripple: ETEL adopts a patented magnetic circuit design (inclined groove or special magnetic pole shape) to minimize cogging and force ripple, ensuring smooth positioning.

Typical applications: CNC machine tool feed axis, large-scale flat printing, heavy-duty material handling, electrode cutting in battery manufacturing, and other scenarios that require high thrust and medium low speed accuracy.

2.2 IL+Series - Ironless Motor

The rotor of the ironless motor does not contain ferromagnetic materials, and the winding is directly encapsulated in a non-magnetic skeleton. The stator is a double row of permanent magnets forming an air gap magnetic field.

Core advantages:

Zero cogging effect: There is no magnetic resistance change in the coreless structure, and the thrust position curve is theoretically completely straight, achieving "zero force fluctuation".

Extremely low inertia: The mass of the rotor is extremely light (usually only 30%~50% of the same thrust iron core motor), and can achieve ultra-high acceleration and velocity (>5m/s or even 10m/s).

No magnetic attraction: There is no attractive force between the rotor and stator, simplifying the design of mechanical guide rails and reducing friction and wear.

Excellent speed stability: Due to the absence of cogging force and low inertia, the speed ripple is extremely low, making it very suitable for high-precision uniform scanning applications such as wafer inspection and flat panel display AOI.

Typical applications: wafer cutting machines, laser direct imaging (LDI), high-speed surface mount machines, optical inspection scanning tables, bio chip sampling machines, and other lightweight, high-speed, and high-precision scenarios.

2.3 Selection Decision Framework

ETEL's product manual provides a concise "Motor Selection Chart" that arranges the IL+and LM series in two dimensions: "sustained force" and "peak force". When selecting, it is recommended to evaluate according to the following steps:

Thrust requirement: Calculate the maximum acceleration thrust (F=ma) and steady-state uniform thrust (overcoming friction) required for the application. The peak thrust determines the upper limit of motor selection, while the sustained thrust determines the heat dissipation design and thermal management scheme.

Speed and acceleration: Ironless IL+is more suitable for high-speed and high acceleration (>5g), while iron core LM is more suitable for medium and low-speed (<3g) but high thrust scenarios.

Accuracy and smoothness requirements: If nanometer level positioning or extremely low speed ripple (<0.1%) is required, IL+is preferred; If system rigidity and anti-interference ability are more important (such as milling), LM is more suitable.

Voltage and driver compatibility: The LM series typically supports higher bus voltages (such as 300Vdc) and is compatible with DSC2P/DSC2V high-voltage drivers; The IL+series is mostly low voltage (such as 48V or 150V) and requires the use of low voltage drivers such as DSCDP/DSCDL.

Heat dissipation method: High continuous thrust (especially LM) usually requires water cooling or forced air cooling; IL+has stronger natural cooling capacity due to low copper and iron losses.

Interpretation of Key Performance Parameters

Whether it is IL+or LM, ETEL provides detailed performance parameter tables, and engineers need to focus on the following:

3.1 Continuous Force

Defined as the long-term output thrust of a motor at rated temperature rise (usually 100 ℃~120 ℃). This value is greatly affected by heat dissipation conditions - the difference in sustained thrust between natural cooling, air cooling, and water cooling can reach 2-3 times. When selecting, the evaluation must be based on the actual heat dissipation capacity of the application (rather than the ideal value).

3.2 Peak Force

The maximum thrust that a motor can provide in a short period of time is usually limited by the peak current of the driver and the magnetic saturation of the motor. The peak thrust determines the maximum acceleration capability of the system, but the duration is usually only a few seconds, and the I ² t heat accumulation needs to be calculated in conjunction with the duty cycle.

3.3 Force Constant (Kt)

The unit is N/A or N/Arms, representing the thrust generated per ampere of current. The larger Kt, the greater the thrust under the same current, but the back electromotive force constant (Ke) also increases accordingly, limiting the voltage margin at high speeds. When selecting, it is necessary to weigh between "thrust/current" and "thrust/voltage".

3.4 Electrical Time Constant

Determined by inductance (L) and resistance (R) (τ=L/R). The time constant affects the response speed of the current loop - motors with smaller time constants (usually iron core motors with larger inductance and higher τ) require lower current loop bandwidth and are relatively easy to debug; Ironless motors have extremely low inductance and small τ, requiring high current loop bandwidth but faster response.

Integrated debugging with ETEL DSC series servo controllers

IL+/LM linear motors must be used in conjunction with ETEL DSC series (DSC2P, DSC2V, DSCDP, DSCDL, DSCDM) digital position controllers. The two are deeply integrated in design, but hardware selection and software parameter settings still need to be noted:

4.1 Encoder interface matching

IL+/LM motors are typically equipped with high-resolution analog cosine encoders (1Vpp) or EnDat 2.1 absolute encoders. The encoder interface (JC5/JC6) of the DSC controller supports:

Analog encoder (K79=0): K55 (increment per pole cycle) and K77 (interpolation factor) need to be set correctly.

EnDat 2.1 (K79=4): Attention should be paid to cable length limitations (≤ 150m, distributed capacitance 90pF/m) and clock frequency (500kHz).

Selection reminder: If the motor comes standard with an 11 μ App encoder (instead of 1Vpp), it is necessary to confirm whether the hardware version of the DSC controller supports it (some early DSCDPs only support 1Vpp).

4.2 Correspondence between motor parameters and K parameters

After selecting the motor model in the "Drive Setting" tool of ETEL Tools, the following K parameters are automatically loaded:

K54 (pole pairs): The linear motor is fixed at 1.

K55 (increments per magnetic pole cycle): determined by the encoder resolution and K77.

K89 (number of phases and PWM frequency): It needs to be matched with the motor winding connection method (star/delta) and the driver PWM frequency. DSCDL is usually set to 20 (two-phase) or 30 (three-phase), with a PWM frequency of 18kHz.

K240 (motor type): 0=straight line, 1=rotation. This parameter affects the display of positional units (mm vs. rad) in ETEL Tools.

4.3 Initialization and commutation parameter adaptation

IL+(coreless) and LM (coreless) need to be treated differently in terms of initialization (Phasing) parameters:

IL+(Ironless): Due to the extremely low inductance of ironless motors, K98 (PWM voltage duty cycle) needs to be reduced during constant current initialization (K90=2) to prevent current overshoot. The manual suggests using K90=2 with appropriate K92 (current amplitude) and K94 (time).

LM (iron core): can choose "pulse initialization" (K90=1) or "constant current initialization" (K90=2). Pulse initialization produces almost no displacement and is suitable for vertical axis or finite stroke applications, but the accuracy is slightly lower (about ± 20% phase).

General recommendation: For motors installed vertically (whether IL+or LM), priority should be given to using small displacement initialization (K90=6) to avoid load sliding and collision with mechanical limits.

4.4 Homing Mode Selection

The zeroing of linear motors usually uses encoder reference pulses (Index) or external home switches. In the DSC controller:

Multi reference pulse encoder (such as LIDA series): K40=12/13 (with mechanical limit) or 20/21 (with limited search stroke), K75 (reference pulse spacing) needs to be set correctly.

Single reference pulse encoder: K40=8/9 (pure Index) or 10/11 (with limit switch).

Origin switch+Index: K40=34~39 (requires K58 to select limit signal source - DIN9/DIN10 or encoder's EHO/ELS signal).

4.5 Current Limitation and I ² t Protection

According to the continuous current and peak current in the motor data manual, set the protection parameters of the DSC controller:

K83 (overcurrent threshold): should be set to about 1.2 times the peak current of the motor (converted to internal units of the controller [ci]).

K84 (I ² t trigger current): usually set as the square of the continuous current multiplied by 0.8192 (see manual calculation formula).

K85 (I ² t integral limit): Calculated based on the duration of peak current to prevent motor or driver overheating.

Special reminder: If using a two-phase linear motor (instead of a three-phase motor), during short stroke reciprocating motion, if the current is concentrated on a few windings, the K84 value should be halved to avoid local overheating.

Selection Cases and Common Misconceptions

5.1 Case 1: High speed wafer inspection platform

Requirement: Load 2kg, acceleration 5g, uniform speed 1.5m/s, speed ripple<0.05%.

Selection: IL+series ironless motor (extremely light rotor, zero cogging force), paired with DSCDL low-voltage controller (± 36V).

Key parameters: K77 set to 3 (11 bit interpolation), K90=2 (constant current initialization), K40=8 (single index returns to zero).

5.2 Case 2: CNC milling machine Z-axis

Requirement: Load of 80kg, acceleration of 1.5g, peak thrust of 1500N.

Selection: LMG series iron core motor (high force density), paired with DSC2P high-voltage controller (325Vdc bus).

Key parameters: K90=1 (pulse initialization, vertical axis zero displacement), K40=0 (mechanical limit return to zero), K83 overcurrent threshold set to 120% of the motor peak current.

5.3 Common selection misconceptions

Misconception 1: Neglecting heat dissipation conditions and using "water cooling" parameters instead of natural cooling, resulting in severe insufficient actual sustained thrust.

Misconception 2: Underestimating the Impact of Force Fluctuations - Choosing an iron core motor incorrectly in applications that require nanoscale positioning, even though ETEL's patented design has significantly reduced force fluctuations, still lacks the zero fluctuation characteristics of ironless motors.

Misconception 3: Mismatched driver voltage level - Low voltage drivers (such as DSCDM) cannot drive high voltage motors, and vice versa.