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While there are many brands and models of Wire EDM machines available today, the three most prominent manufacturers are Elox, Japax, and Mitsubishi.

While each of these companies manufacture similar products, there will always be some varying features such as the User-interface with the CNC controller, the numbers of wires, be it a 4-axis or 5-axis Wire EDM machine, type of electrical current (AC vs. DC), and the gauges of wires that can be used. Another very big difference will be the size of the tank in which the manufacturing is accomplished.

Some examples of specifications for one model from each of these companies are:

Elox Fanuc Model M - (the Fanuc indicating the type of CNC controller that is a component of the Elox Wire EDM) has an X-axis path of 20, a Y-axis path of 14, and a Z-axis path of 10

Japax Wire EDM Model LDM-S - has a Y-axis path 13.8 and capable of machining a work piece with the measurements of 15.7 x 19.7 x 5.9 and a table that moves 7.9 x 13.8

Mitsubishi Wire EDM Model DWC 110 H-1 - has an X-axis of 12, a Y-axis of 18, and a Z-axis of 10

Each of these models only represents one of many different models offered by their respective manufacturer. Variations will be observed from model to model with some differences including the distance that each axis wire can travel, the size of product that can be manufactured and the CNC controller.

When selecting a wire EDM machine, one must take into consideration the product that will be manufactured, the degrees of tolerance and variances that are allowed, how detailed the cut will be, and not least importantly, the funds available for purchasing the wire EDM.

While Elox, Japax and Mitsubishi are three prominent manufacturers of wire EDM machines, remember that there are also other manufactures of wire EDM machines.

What is a PID controller?

A PID (Proportional Integral Derivative) controller is a common instrument used in industrial control applications. A PID controller can be used for regulation of speed, temperature, flow, pressure and other process variables. Field mounted PID controllers can be placed close to the sensor or the control regulation device and be monitored centrally using a SCADA system.

Example: Temperature Control using a Digital PID controller

A typical PID temperature controller application could be to continuously vary a regulator which can alter a process temperature. This may be a pulsed switching device for electrical heaters or by opening and closing a gas valve. A heat only PID temperature controller uses a reverse output action, i.e. more power is applied when the temperature is below the setpoint and less power when above. PID control for injection and extrusion applications often employ additional cooling control outputs and usually require multiple controllers.

A PID controller (sometimes called a three term controller) reads the sensor signal, normally from a thermocouple or RTD, and converts the measurement to engineering units e.g. Degrees C. It then subtracts the measurement from a desired setpoint to determine an error.

The error is acted upon by the three (P, I & D) terms simultaneously:

PID Controller Theory

The following section examines PID controller theory and provides further explanation of the question `how do PID controllers work'.

Proportional (Gain)

The error is multiplied by a negative (for reverse action) proportional constant P, and added to the current output. P represents the band over which a controller's output is proportional to the error of the system. E.g. for a heater, a controller with a proportional band of 10 deg C and a setpoint of 100 deg C would have an output of 100% up to 90 deg C, 50% at 95 Deg C and 10% at 99 deg C. If the temperature overshoots the setpoint value, the heating power would be cut back further. Proportional only control can provide a stable process temperature but there will always be an error between the required setpoint and the actual process temperature.

Integral (Reset)

The error is integrated (averaged) over a period of time, and then multiplied by a constant I, and added to the current control output. I represents the steady state error of the system and will remove setpoint / measured value errors. For many applications Proportional + Integral control will be satisfactory with good stability and at the desired setpoint.

Derivative (Rate)

The rate of change of the error is calculated with respect to time, multiplied by another constant D, and added to the output. The derivative term is used to determine a controller's response to a change or disturbance of the process temperature (e.g. opening an oven door). The larger the derivative term, the more rapidly the controller will respond to changes in the process value.

Tuning of PID Controller Terms

The P, I and D terms need to be "tuned" to suit the dynamics of the process being controlled. Any of the terms described above can cause the process to be unstable, or very slow to control, if not correctly set. These days temperature control using digital PID controllers have automatic auto-tune functions. During the auto-tune period the PID controller controls the power to the process and measures the rate of change, overshoot and response time of the plant. This is often based on the Zeigler-Nichols method of calculating controller term values. Once the auto-tune period is completed the P, I & D values are stored and used by the PID controller.