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Simulation and offline programming
Edited by Dr Ken Young
1 Introduction
The DLR light-weight robots (LWR) have been developed for application areas which are fundamentally different from the ones of classical industrial robotics. The strengths of industrial robots are especially high positioning accuracy (repeatability and absolute accuracy), high speed, durability, and robustness, as well as the relatively low price. Therefore, today's industrial robots are used especially in well structured environments, in which the position and shape of the parts to be manipulated are well determined and in which collisions with the environment and humans can be estimated and excluded in advance. High performance is achieved for fast tasks which are repeated numerous times. Generally, the high positioning accuracy requires high stiffness at the price of high robot mass relative to its payload.
In contrast, the robotic systems developed at DLR (arms, hands, a humanoid manipulator) are designed for interaction with humans in unstructured, everyday environments. In such applications, high absolute positioning accuracy cannot be exploited due to limited accuracy of position information about the surrounding environment, while its side-effects in design (high stiffness and mass) are clearly undesired. The DLR robots (Figure 1 [Figure omitted. See Article Image.]) are thus designed for application areas which are generally not covered by industrial robots, but are still ongoing research topics. Typical examples are:
- assembly processes for which the position estimation for the mating parts and/or the positioning accuracy of the robot is significantly below the assembly tolerance;
- applications in which the robot works in immediate vicinity of humans and possibly in direct physical cooperation with them; and
- mobile service robotics applications (arms mounted on mobile platforms), for which the information about the position of the robot and the surrounding objects, as well as about the dimension of these objects is afflicted with relatively high uncertainty.
For the mechanical design, the mentioned applications determine the requirement of a low robot mass compared to the payload in order to enable mobility and minimize the injury risk. However, the robots are operated at relatively low velocities compared to industrial robots, thus enabling higher gear ratios. The main requirements for the electronic design result from the high number of sensors, such as joint torque sensors, redundant position...