Guidelines for Key Technologies of ETEL LMG/LMS Linear Motor Integration

Guidelines for Key Technologies of ETEL LMG/LMS Linear Motor Integration

Introduction: Evolution and Selection Challenges of Direct Drive Technology

In the fields of precision manufacturing and semiconductor equipment, linear motors are gradually replacing traditional transmission mechanisms such as ball screws and toothed belts. Its core advantage lies in the "zero transmission chain" - the load is directly coupled to the rotor, eliminating reverse clearance, elastic deformation, and mechanical wear, significantly extending the system's lifespan and maintenance cycle. As a brand that has been focusing on direct drive technology for over 30 years, ETEL's LMG, LMS iron core series, and ILF+, ILM+coreless series cover a wide range of scenarios from high dynamic light loads to high sustained heavy loads. However, a common misconception in engineering practice is that the selection is based solely on peak force and ignores the thermal boundary, or the "inflection point" of the force velocity curve is not properly handled, resulting in the inability to meet the speed standard. This article will take LMG/LMS as the main line, integrate ironless solutions, and systematically explain the complete integration path from mechanical calculation to heat dissipation design, from encoder matching to structural rigidity.

Selection boundary between iron core and non iron core technologies

2.1 Force density advantages of iron core motors (LMG/LMS/LMA)

The iron core structure utilizes laminated iron cores to converge magnetic flux, generating a much higher continuous force than without an iron core at the same volume. The LMG series is compact and economical, with a peak force of up to 3650 N and a maximum acceleration of 20 g. It is suitable for medium to high load scenarios such as flying pin testing and wafer inspection that require high acceleration and deceleration. LMS improves the continuous force by about 30% on the basis of LMG, and the mechanical interface is fully compatible - the thickness is only increased by 7 mm, the installation hole position and magnetic circuit spacing remain unchanged, providing users with a "plug and play" upgrade path. Specifically, LMA is optimized for high duty cycle (high sustained/peak power ratio) applications, and its 600 VDC withstand voltage design can reduce driving current and minimize I ² R losses.

2.2 Zero cogging force characteristics of ironless motors (ILF+/ILM+)

The ironless rotor does not contain magnets or laminations, has extremely low motion mass, can accelerate up to 30 g, and has no magnetic attraction, making it an ideal choice for air bearing platforms. Its force current linearity is excellent, and the speed fluctuation can be less than 0.1%, making it particularly suitable for long stroke scanning or low jitter optical detection. However, due to the limitation of the heat dissipation path (no thermal conductivity difference in the iron core), its sustained force is usually lower than that of models with the same size iron core, and a forced air cooling option is required to increase the duty cycle. When selecting, it must be clear that if the application pursues ultimate speed stability (such as wafer positioning) and the load is light, priority should be given to ILF+; If high thrust and frequent acceleration and deceleration are required, LMG/LMS is better.

Core calculation for mechanical selection: peak force and sustained force

3.1 Peak force calculation

The peak force (Fp) is equal to the total mass of motion (load+rotor) multiplied by the maximum acceleration, plus frictional force, cutting force, and external disturbances. The peak force given in the ETEL sample is usually the instantaneous capability at a 5% duty cycle, and in practical applications, it is necessary to ensure that the peak current of the driver does not exceed the allowable value. Engineering suggestion: Reserve a margin of 20% to 30% to avoid derating caused by voltage drop or temperature rise.

3.2 Continuous force and heat dissipation

Continuous force (Fc) is the key to evaluating the average heat generation of a motor. During a complete motion cycle, the effective force value (RMS) of each stage needs to be calculated, and the formula is:

Frms=∑Fitwo⋅ti

TF rms= T∑F itwo⋅t i

When Frms

When the Fc value given based on a specific heat dissipation area (such as a 300 × 300 mm aluminum plate) in the sample is less than, the motor temperature rise is within a controllable range. But if the actual installation surface is smaller than the reference area (such as installing on a ceramic base through insulation pads), Fc needs to be downgraded. On the contrary, if installed on a large water-cooled plate, it can sustainably output higher thrust. ETEL explicitly proposes the concept of "assumed exchange area" - this value directly affects the calibration of continuous force, and the actual thermal contact conditions should be confirmed with the manufacturer during the design phase to avoid insufficient performance in the later stage.

3.3 Blocked rotor and three-phase unbalance