Introduction to ISAC Adaptive Servo Controllers

What is the most important expectation from a Servo Controller worthwhile called a good one?

At present, many products named “Industrial Servo Controller” are in the market; however, to select a good one for the desired performance is still a difficult task. You need to know what your plant’s desired response to be and exactly which performance to be focused on.

We think as follows,

Performance to be expected

In the selection of a servo controller, the following characteristics should be considered as most important and inevitable:

1. Response
How and at which velocity should your plant’s output, such as cylinder-rod displacement, pressure, flow, velocity, temperature, etc., reach to its desired set point?

The overrun or overshoot has to be evaded in the process of controlled trajectory, while achieving the fastest response possible.

2. Steady-State Error (Set-point Accuracy)
There would be no meaning in the design of a servo system if there remains a substantial difference between the desired and actual response even though it is achieved within the acceptable time. To which degree can you decrease the steady-state error?

Set-point accuracy is the most important requirement for any plant under consideration and that steady-state error must be eliminated for overall system accuracy.

Easy approach to handling and adjustment

Suppose you used a servo controller and were satisfied with the response with respect to above described specifications. Would you say that it is an effective servo controller to the level of satisfaction? What about if controlled performance deteriorated in about half a year due to parameter variations or changes in operating conditions? What about if plant engineer spent half a month to re-adjust controller parameters for the new operating conditions?

Robustness is another essential property of a servo controller for today’s highly complex systems.

Today’s industrial servo controllers, without any doubt, must possess all of the above listed properties. However, many of them available in the market do not possess these properties. We therefore invite you to explore and experience the excellent performance presented by the I-SAC adaptive servo controller.

 

 

  

Controller Specifications

Fig. 1 shows an example of a step response of PID and I-SAC Servo Controller in case of setting target value to one in a typical cylinder-positioning control system. While any PID control has an overshoot and reaching the target in an oscillating mode, I-SAC is realizing a smooth and fast response without any oscillations due to its proprietary high-gain feedback. As to the steady-state error, I-SAC can make it totally zero because of its integration compensation feature.

Robustness Against Variance of Circumtances

Fig. 2 illustrates a typical result of I-SAC controller and its superior performance compared to a PID controller. For the cylinder positioning control system (same as in Fig. 1), we gave three different masses to the cylinder while maintaining same parameters for the controllers. As you can see from the figure, the response is unacceptably oscillatory in the case of PID control, which requires re-adjustment of controller parameters by plant engineers. On the other hand, I-SAC provides an excellent robust performance due to its adaptive control structure.

Adjustments of Parameters

There are only a few parameters to be initially adjusted in the I-SAC. Furthermore, it is not necessary to use gain, phase characteristics and/or transfer function of the system as in PID control. It is just enough if an engineer adjusts confirming response at the very beginning.

Fig. 1	Fig. 2

Now, we hope that you realize I-SAC is the only choice, if you want to design high performance servo controller and also hope that you will utilize our controller to its best replacing PID or other servo controllers. We are confident that you will be extremely satisfied once you use our I-SAC for your variety of applications.

 

 

 

Application Examples

 

1. Remote Control Construction Machine Robot (pneumatic: position control)
Apparatus operated remotely in the hazardous area, retrofitting pneumatic cylinders on the joystick of a bulldozer or a shovel machine, I-SAC was used as servo controller and got the operator’s manipulation to its fidelity.

 

2. Powder Press Machine 1 (hydraulic: position/load control)
I-SAC MX (2 axes), switching positional control to pressure control, made it possible to get target load with fast response yet without overshoot, thus realized high quality production. In addition, its integrator function adaptively compensated the change in output due to ambient temperature drift and no parameter re-adjustment was needed.

 

3. Powder Press Machine 2 (hydraulic: position control)
Used for hydraulic servo system of the upper mold tool positional control, resolved steady-state error arisen from unbalanced pressure in the lower mechanical mold (base) tool, achieved positional accuracy to 10 μm.

 

4. Mold Traverse Equipment (pneumatic: position control)
Mold tool weighing over one ton was transferred to the distance of approximately two meters and was changed to another mold tool. It took over one minute for transferring the load with the conventional system. The time was reduced to approximately 15 seconds when I-SAC was used. It was also possible to easily minimize undesired mechanical shock and impact during tool transferring process.

 

5. Testing Apparatus of Pitot-Tube (pneumatic: pressure control)
Used in pneumatic pressure control for the test apparatus of an air fighter’s velocity measurement system employing Pitot-Tube. With the use of I-SAC, settling time was shortened and utmost performance was achieved that was otherwise impossible by any conventional servo controllers due to their poor versatility.

 

6. Chemical Plant (pneumatic: pressure control)
Replacing PID controller with our I-SAC has successfully stabilized apparatus of high temperature compressed air supply system. Pressure change was decreased by one third, resulted in enhanced product quality without renewing the plant equipment.

 

7. Electric Servo Motor Control System
As it is well known, the manufacturers of electric servo motors provide their own servo controllers. However, in almost all the cases they employ conventional PID controller in their products. If you wish superior performance, why not try our I-SAC control system!

 

 

 

 

 

■I-SAC MX Servo Controller

 

 

●Motion Program User can set a motion profile into I-SAC-MX and can automatically control the plant according to the profile. Various interfaces such as with PLC can be made by giving a special target value needed. ●Various Handshakes Servo On/Off, Automatics Zero Searching, In-position output, etc. are equipped and can be friendly interfaced with PLC, etc. ●2-Axis Independent Control and Axis Switching Two independent controllers are built-in and can switch axis during operation. An example is a firstly position control and then immediate switch to load control in real time.