AN2350 datasheet(6/41 Pages) STMICROELECTRONICS

6 / 41 page

An overview on robotics

AN2350

6/41

Since the links of a robot arm may rotate and/or translate with respect to a reference

coordinate frame, the total spatial displacement of the end-effector is due to the angular

rotations and linear translations of the links.

Denavit and Hartenberg proposed a systematic and generalized approach of utilizing matrix

algebra to describe and represent the spatial geometry of the links of a robot arm with

respect to a fixed reference frame. This method uses a 4 x 4 homogeneous transformation

matrix to describe the relationship between two adjacent rigid mechanical links and reduces

the direct kinematics problem to finding an equivalent 4 x 4 homogeneous transformation

matrix that relates the spatial displacement of the hand coordinate frame to the reference

coordinate frame. These homogeneous transformation matrices are also useful in deriving

the dynamic equation of motion of a robot arm.

In general, the inverse kinematics problem can be solved by several techniques. Most

commonly used approaches are matrix algebraic, iterative, or geometric. A geometric

approach based on both the link coordinate systems and the manipulator configuration has

been used for the industrial wafer handler to which this application note refers.

1.1.2

Singularity

A significant issue in kinematic analysis surrounds so-called singular configurations.

Physically, these configurations correspond to situations where the robot joints have been

aligned in such a way that there is at least one direction of motion (the singular direction[s])

for the end effector that physically cannot be achieved by the mechanism. This occurs at

workspace boundaries, and when the axes of two (or more) joints line up and are

redundantly contributing to an end effector motion, at the cost of another end effector DOF

being lost.

1.2

The industrial wafer handler

This section describes the main characteristics of an industrial wafer handler, used as a

case study for a multiaxial planar manipulator family.

The structure of the manipulator consists of two arms with six joints (one prismatic joint and

five revolute joints) arranged in order to have the motion axes parallel to each other.

The illustration below shows the relation between the axis control and the robot

components.

AN2350 Datasheet(PDF) 6 Page - STMicroelectronics