1. Field of the Invention
The present invention relates generally to control systems, and more particularly, the present invention relates to adjustment and calibration of electromagnetic devices.
2. Description of Related Art
Electromagnetic devices are well known. One example is an E-I core actuator, which is a type of electromagnetic linear motor so named because of its two main components. The first component is the E-core, which is a three-barrel structure having a shape that resembles the letter “E” with an insulated electric coil wire wound around the center bar and a source of current supplying current to the coil. Current running through the coil creates an electromagnetic field which attracts an associated I shaped core. Thus, an electromagnetic force is exerted across the width of a gap between the E-core and the I-core. When a constant current is supplied to the coil, the force of the electromagnetic field may change as the gap distance changes. This change in force is often referred to as the output force gain of the E-I core system.
E-I core electromagnetic devices may be used to precisely adjust the position of an object. Unlike, for instance, a bi-directional voice coil motor which also provides precision positioning, E-I core electromagnetic devices use substantially less electric current and therefore less energy in the form of waste heat. Another benefit of E-I core electromagnetic devices is the reduction of vibration during precision motion. For instance, precision motion is frequently needed in machining, lithography, and other strict tolerance manufacturing applications e.g., in stepper and scanner machines used in the semiconductor industry. Typically, the goal is to provide precise adjustment of, for instance, a sampler or work piece stage in three dimensions.
In the prior art, calibration and adjustment is often done through a mechanical adjustment, which has been found to be time consuming and imprecise, especially due to problems of drift attributable to thermal or other effects. This both degrades performance and reduces system throughput, since time is required for the actual calibration. An improved calibration method would be very desirable for such systems.
When using an E-I core electromagnetic device, the output force gain may be used to calibrate the device for precision adjustments, such as for positioning components of a precision machine. Precisely positioning machine components is difficult because the output force gain varies due to effects such as part-to-part variance, geometric mounting inaccuracy, and a dynamically changing gap distance during operation of E-I core electromagnetic device. Using a gap distance measurement, E-I core commutation equations may be used to model the output force gain. These models require burdensome hand tuning for each E-I core electromagnetic device. Further, even with a model, it is difficult to obtain precise measurements when dealing with large ranges of gap distance. Moreover, equations used in models, such as force gain model equations, become ineffective when gap distance information is unavailable or the force gain changes due to unmodeled factors.
Thus, there is a need for an improved method of modeling output force gain in electromagnetic devices to create precise measurements and adjustments. Further, there is a need for an improved method of calibrating the output force gain for E-I core electromagnetic devices.