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 Brain: Robotic Arm Controller

A typical robotic arm controller performs the following functions:

• To solve kinematics: Unlike many automated machines, robots are mechanical coupling devices. What this means is that by moving a single axis, all the other axes will move too. As such, robotic arm controller needs to provide a solution to calculate kinematics and reverse kinematics equations to enable the robotics arms to move in coordinated fashion. Kinematics is the mathematical representation of the robot, including its size, configuration and the relationship of each axis to the mechanism as a whole. This coordination is the basis for sensor integration, path following, straight line movements, and other features common to industrial robots.

• To deliver speedy, accurate and repeatable operation. Robots are expected to perform uniformly throughout their whole work envelope, with a range of payloads. In addition, mechanical coupling, complex mechanisms, added to the complexity of needing to balance speed and precision by managing system resonance and vibration issues.

• To offer sensor integration: Robotics controller is required to handle the integration of complex sensors such as machine vision, force sensing, and conveyor tracking. At minimum a robot motion control system is expected to adjust points and paths in real time based on sensor information.

 Robotic Programming

• Teach Method: A teach pendant is used to control and program the robot. Operator can teach the robot by driving individual robotic joints independently (named joint co-ordinate), drives robot's tool centre using the X, Y, Z axes of the global axis system (called global co-ordinate), or by utilising tool co-ordinate system for teaching. The tool co-ordinate system is similar to the global co-ordinate system but the axes in this case are attached to the tool centre point of the robot. This system is especially useful when the tool is near to the work piece.

With many robots it is possible to set up a co-ordinate system at any point within the working area (work piece co-ordinate) when teaching.

These locations are then stored with names that can be used within the robot program.

This method of programming is very simple to use where simple movements are required. However, when teaching, the robot cannot be run in production, this reduces the machine utilization rate.

• Lead Through: This programming method is mainly used by spray painting robots. The robot is programmed by being physically moved through the task by an operator. This is exceedingly difficult where large robots are being used and sometimes a smaller version of the robot is used for this purpose. Any hesitations or inaccuracies that are introduced into the program cannot be edited out easily without reprogramming the whole task. The robot controller simply records the joint positions at a fixed time interval and then plays this back.

• Off-line Programming: Similar to the way in which CAD systems are being used to generate NC programs for milling machines it is also possible to program robots from the CAD models of the robots, fixtures and accessories. The program structure is built up in much the same way as for teach programming but intelligent tools are available which allow the CAD data to be used to generate sequences of location and process information. The benefits of this form of programming are:-

• Reduced down time for programming.
• Programming tools make programming easi06-Apr-2009uces product lead time.
• Assists cell design and allows process optimization.

However, because off-line programming is not accurate, it requires adjustment interactively on the factory floor until all positions and orientations are correct because the robot can run in the production.