CASE STUDIES IN MECHATRONIC SYSTEMS:
A Pick and Place Robot:
The robot has three axes and about these three axes only motion occurs.
The following movements are required for this robot
Clockwise and Anti-clockwise rotation of the robot unit on its base
Horizontal Linear movement of the arm to extend or contraction
Up and down movement of the arm and
Open or close movement of the gripper
The above movements are accomplished by the use of pneumatic cylinders operated by solenoid controlled values with limit switches.
The limit switches are used to indicate when a motion is completed.
The clockwise rotation of the robot unit can be obtained from a piston and cylinder arrangement during its extension and that of counter clockwise during its retraction.
The upward and downward movement of the arm can be obtained from a piston and cylinder arrangement during the extension and retraction of a piston respectively.
Similarly, the gripper can be opened or closed by the piston in a linear cylinder during its extension.
The micro controller used to control the solenoid values and hence the movements of the robot unit. The type of microcontroller used in M68C11.
A software program is used to control the robot.
Eight C port lies PC0 – PC7, are used to sense the position of eight separate limit switches used for eight different robotic movements.
Also one line from port D is used to start or stop the robot operation.
The switch in its one position will provide +5V (a logic high signal), to the corresponding port lines and the switch in another position will provide 0V (a logic low
signal), to the port lines.
So the two positions of a switch will provide either a logic high or logic low to the corresponding PC0 – PC7, and PD, lines.
Eight part B lines (PB0 – PB7) are used to control eight different movement. These are Base CW, Base CEW, Arm extends, Arm retract, Arm up, Arm down Gripper close and
Gripper open of the robot.
PB0, is connected to the Triacoptoisolator through a resistor.
TRIAC isolator consists of LED and TRIAC.
For example, when the base has to rotate in clockwise direction, a high signal is sent through line PB0
The diode is forward biased and the TRIAC optoisolation operates, regulating the supply to the solenoid value which in turn operated the piston rod of the pneumatic cylinder.
The base clockwise continues the rotation till it reader the position of second limit switch