Why control systems are important for a LEGO toy?
Nowadays, a toy is not just a toy. A toy can have a lot of functions on it. It is more attractive for children if a toy is controlled by remote control. Application theories on toys are called control systems. The objective of the LEGO robot project is modeling and designing control systems for the robot used to drive two motors as wheels.
A Control system is not only important for a toy, but also widely used in our life. Such as environmental temperature, humidity, water level, pressure controls, position control of mechanical structure, and speed control. A few examples of the control system applications are controlling water temperature of our washing machine, temperature of the air conditioner, and cruise control on our cars.
What is a LEGO robot?
LEGO robot is a toy with two motors as wheels. It is like a toy car with only two wheels. The robot can be connected to the computer by using Wi-Fi. All the instructions and commands are loaded into the robot by using simulation from MATLAB – a high-performance language for technical computing. And simulation is a tool from computing. Simulation can simulate the control system results and output different parameters and graphs on the computer.
What is a Control System?
The control system is a system involving instructions. The control system includes input, executive system, effector system and output. The inputs in this project are instructions. The executive system is simulation command. The effector system is the robot. For example, if we want the robot to move forward or backward, it can be made by instructions from control system. Then the output is the movement of the robot.
What types are the Control Systems?
As diagram above illustrates, there are two types of control systems we are developing on this project. The first type is open-loop control system, also called non-feedback control system. The characteristic of open-loop control is use of a controller that approximates the inverse of the system to be controlled. The input will not be affected by the output. Waving the baseball stick to hit the baseball is a good example. The input is the feeling of there is a baseball coming. Then the information of baseball coming is sent to the executive system. The executive system evaluates the correction rate of this information. If the baseball is coming, then the executive system sends command to the effector system. When the effector system receives the command, the output is waving the baseball stick to hit the baseball.
The second type is closed-loop control, also called feedback control system. The characteristic of closed-loop control is the output of the control system is returning to the input of the system. The feedback information is compared with the original input information. And the results of the comparison are applied on the system to prevent the system from deviating from the predetermined target. The control system utilizes negative feedback, combines signal forward path and feedback path to form the closed-loop control system. Catching a baseball is good example. The visual information plays a feedback role while the hand is moving to catch the baseball. The error is the actual direction of hands movement and correct direction is the desired hands movement. The implementation of the system decides how to change by making a comparison. Then we can make sure the hands move in the appropriate direction to catch the ball. So using the feedback information to adjust the action is called closed-loop control system.
How to choose correct types of Control Systems?
By choosing the open-loop control system on the robot, the system is unable to know when the external force is applied if there is an external force applied on the robot wheels. Then the system is unable to auto corrects the output parameters and graphs. The robot will follow the wrong path after the external force is applied. The open-loop control system unable to judge the disturbance, it just executing the commands. So the open-loop control system is not accurate enough. But the system is more stable and lower cost on production. For example, the vending machines and automatic production lines are using the open-loop control. The accuracy and the stability of these systems are not the most important part. But as we know, the number of the vending machines and automatic production lines are huge, we need the system to be simple and easy to construct. And the lower cost on production is also important.
By choosing the closed-loop control system, the closed-loop control system can auto corrects the moving path after the force is applied. The output parameters and graphs only change while the external force was applied. It will go back to normal when the force disappears. Then the robot will follow the original path. The closed-loop control system evaluates the error and does the auto correction. The closed-loop control is more accuracte, but the system is not very stable due to the complex system. And the working principles and structures of closed-loop control system are more complex, it will be more difficult to implement, and it will cost more on production. For example, we can’t use open-loop control on the car’s cruise control. The cruise control needs the system to be very accuracy. If we set a cruise speed on the car, the system should always check the actual speed with the set speed to make sure the car is running at the correct speed. This is more about safety, so we must choose to use the closed-loop control even if it is more expensive on production.
The control system is not only important for a toy, but also important for our life. It exists everywhere and widely used in our life.
Changmeng Lin 