Linear motors are currently used inside robots, actuators, precision tables/stages, fiber optics and photonics alignment and positioning, assembly, pick and place systems, machine tools, semiconductor equipment, electronic manufacturing, inspection systems requiring responsive control at high bandwidths, vision systems, and in many other industrial motion control applications. Precision motion control with disturbance observer for pulsewidth-modulated-driven permanent-magnet linear motors,” IEEE Transactions on Magnetics, vol. The basic idea of disturbance observer is to estimate the real-time system disturbance and output equivalent disturbance then conduct compensation to the control output 18 Hwang and Seok designed Jacobian linearized observer for the hybrid stepper linear motor to ensure that the state estimation converged to the true value and designed an input-output feedback linearization controller for the speed loop and position loop 19 Cho et al. proposed a periodic adaptive disturbance observer to weaken the periodic disturbance in repeated motions 20 However, the traditional observer does not use the previous system motion information, so that it could not fully compensate for the spatial periodic force ripple, which is common in many applications, such as lithography machine, numerical control machine tool, and other high-precision manufacturing equipment. Basically iron core motors provide high force and low cost, but the cyclical variation of moving force within the magnetic field (cogging) has negative side effects on the precision of the positioning device due to limited bearing stiffness.
Typically, two types of brushless linear motors are used in magnetic direct drive technology: ironless linear motors and iron core linear motors. Unlike rotary motors, where the rotor spins and the stator is held fixed, a linear motor system can have either the force or the magnet track move (most positioning system applications use a moving force and static track). Linear servo motors typically employ 3 phases and the motion controller drives sinusoidal currents into the 3 phases to provide constant force for extended travel. For more information on Linear stepper motors, visit www.intellidrives.com for more information.
Linear Motors are typically integrated in motion systems that require the best dynamic response and performance while providing the advantage of no inherent drive wear. A power supply system for a linear motor comprising a plurality of driving coils disposed along the track for a running body for generating a shifting magnetic field to drive the running body, power converter means for feeding the plurality of driving coils with electrical energy, a plurality of switches responsive to the movement of the running body for selectively electrically connecting each of the driving coils to the power converter means, a first reactive power controller continuously electrically connected to the power input side of the power converter means, and a second reactive power controller selectively electrically connected to the power input side of the power converter means in accordance with the movement of the running body, whereby the steady reactive-power is compensated for by the first reactive power controller and the reactive power which varies with the movement of the running body is compensated for by the second reactive power controller. Kim et al. designed a feedforward controller to compensate force ripple in a coreless linear motor using a T-type magnet array, and the experiment verified its effectiveness 7 Bascetta et al. identified the force ripple model of brushless AC motors by frequency domain method and performed direct compensation 8 Zhu et al. extracted and compensated the force ripple of the PMLM using the vector control method 9 Otten et al. combined feedback control and neural network feedforward control based on the simplified second-order model of linear motor, and the results show that the online learning controller has great application in tracking control tasks 10 Tan et al. designed a compound control structure in linear motor system, including a simple feedforward part, a PID feedback part, and an adaptive feedforward compensator.
Iron core Linear Motors operate in conjunction with a single magnet track and are ideal for general automation applications whereas Ironless core Linear Motors are usually matched with a ‘U’ shape magnet track and offer a superb smooth velocity/positioning control for high end applications. The V-551 linear motor stage uses ironless motors, but instead of moving the coils, the magnetic track is attached to the platform. PI offers the broadest and deepest portfolio of nanometer precision motion technologies, from piezo-driven nanopositioning and scanning stages to motorized 6-axis hexapod positioning systems.
The low-acceleration, high speed and high power motors are usually of the linear synchronous motor (LSM) design, with an active winding on one side of the air-gap and an array of alternate-pole magnets on the other side.
