Stroke control is extremely common and prevalent in automatic control. Within the scope of motion control , stroke control can be further divided into linear and curvilinear, forward and backward and up and down. If we further subdivide them and observe their characteristics, we get: linear – forward, backward, left, and right on a plane; curvilinear – regular and irregular curves; forward and backward – after defining the direction in a plane, forward and backward becomes forward and backward; up and down – forward and backward in the vertical direction becomes up and down. This division may differ from the definitions in textbooks, but these descriptions summarized from practical applications are easy to understand and facilitate communication.
From the perspective of stroke control, it is essentially a type of motion control . Since it is motion control, it inevitably involves the concepts of motion and control. Motion includes uniform motion, uniformly accelerated motion, and accelerated motion. Within these motion modes, different control methods exist under different loads. For ease of discussion, we will only discuss stroke control from the perspective of circuit control. When the control unit receives a motion command, it supplies power to the motor according to the required drive method. The high-speed rotation of the motor, through the gearbox, drives the walking mechanism to achieve motion. During the motion, relevant information is fed back to the control unit. After processing the feedback information, the control unit issues new drive commands to continue or stop the motion process (see block diagram).
Assuming the travel program is established correctly, the first thing to address is the travel limit switch. This is crucial for both horizontal and vertical movement of the controlled object, as it directly affects system safety. The most common and reliable method is to install a limit switch XW1 and a limit switch XW2 at each end of the travel path.
The limit switch is a two-terminal component connected in series with the contactor coil and then into the control circuit. There is a crank on its housing. When the traveling mechanism moves to the limit position, it will push the crank to rotate, and the limit switch will cut off the power supply to the contactor coil, causing the traveling motor to be de-energized. At this time, the traveling motor can only start in reverse (see control diagram for details).
Motor forward and reverse control diagram
As can be seen from the control diagram above, when AN1 is pressed, forward start occurs, J1 is engaged, and J1-1 closes to keep J1 energized when AN1 is released. The normally open contact of J1-2 closes, connecting the motor power supply, and the normally closed contact of J1-3 opens, de-energizing point B and preventing the reverse button from operating. When AN2 is pressed, J1-1 opens, stopping forward operation. If the forward travel limit switch XW1 is triggered, the forward control circuit will also be de-energized. After J1-2 opens, the motor loses power and stops running, and forward operation cannot continue. When AN3 is pressed, reverse start occurs, J2 is engaged, and J2-1 closes to keep J2 energized when AN3 is released. The normally open contact of J2-2 closes, connecting the motor power supply, and the normally closed contact of J2-3 opens. XW1 closes again under the action of spring force, preventing the forward button from operating. This forms an interlock between forward and reverse operation. Similarly, when AN4 is pressed, J2-2 disconnects, stopping the reverse movement. If the reverse travel limit switch XW2 is activated, the reverse control circuit will also be de-energized. Therefore, regardless of which direction of travel power is cut off, the power supply for the reverse direction should not be disconnected. This ensures that the traveling mechanism does not become stuck when it reaches a certain limit position. The limit switch plays a role in protecting the system at the limit position. In most cases, travel control still requires manual operation for starting and stopping, or consideration of start and stop during program design. For example, in a system with uniform motion, the formula: distance = speed * time can be used for time control. In non-uniform motion environments, the travel must be controlled according to the system's operational requirements, or a corresponding control program must be developed. In such cases, fixed-point position control is often used, such as the "leveling control" in vertically running elevators. With technological advancements, current magnetic induction fixed-point control switches or magnetic induction limit switches are more sensitive and faster-acting than mechanical control and limit switches.
