Assembly robots find wide applications in electric and electronic fields where a short-cycle time and the capacity of small, precise parts assembly are important requirements.
The role of robot for use in the assembly work is as follows:
(1) Odd-Shaped electronic components insertion in printed circuit boards.
(2) Small, precise parts assembly.
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(3) Palletizing and de-palletizing components in boxes.
The robot basically comprises of a suitably designed body and a control unit. It is possible to connect the control unit with RS—232 C link to a central computer system.
Fig. 35.4 shows a typical horizontal articulated type robot which has a first arm, second arm, wrist up-down and twisting axes at four freedoms the end of the second arm to achieve four freedoms of motion. DC servomotors are adopted to drive the arms. In order to simplify the structure of the first arm and second arm, the motors are mounted on the rotation axes, and the arms are driven by the reduction devices.
On the other hand, the motors for wrist up-down and wrists twisting are mounted in caving parts of the first arm and second arms to make the arms lighter; and they are driven by synchronous belts. Such a robot is designed to achieve maximum speed of 2.2 m/sec and repeatability of ± 0.05 mm. It employs teaching playback method and point-to-point path control method.
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The memory employed has capacity of storing 500 points and 500 steps. The input and output channels are 10 each.
Fig. 35.5 shows the system configuration of the control unit. All the processes such as servo control, teaching box input and display, and external interface are done with only one 16-bit microprocessor C.P.U. The all-digital software servo system is adopted as the servo control method.
In this system the software calculates the position and velocity from the counted pulse data of the rotary encoder, and figures out the PWM (pulse width modulation) data with servo constants. Moreover, in order to acquire quicker acceleration and deceleration and to eliminate vibration, software performs acceleration and deceleration (according to a cycloid curve) and integral compensation.
If the control unit detects servo failures such as overrun and encoder signal break, it will stop the robot immediately in order to improve reliability and safety. The content of failures are displayed in the teaching box and thus failures can easily be found and counteractions made.
To achieve automatic start-up of robots, concentrated teaching data administration, and administration of many robots by a host computer, the RS-232 C interface for computer linkage is provided.
The functions achieved by computer linkage system are as follows:
(1) The robot can be operated automatically by the remote operation function which can select such functions as starting up, stopping the robot and job selection.
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(2) Teaching data can be memorized is an external device such as a floppy disk due to the uploading and downloading function (for program data and position data).
(3) Off-Line programming can be achieved by inputting or editing teaching data with a computer.
(4) By connecting a vision system to a computer, the computer can process data from the vision system and send the converted data to the robot for position correction.