# Finding Optimal Manipulator Arm Shapes to Avoid Collisions in a Static Environment
## 1 Introduction
### New Approach  
Although industrial robots are universal systems, in real applications, they usually operate as single-purpose machines and repeat the same task in an enclosed work cell that represents a completely static environment (except for well-defined material transfer). In some cases, using a commercially available universal industrial robot can be very problematic, and could, for example, involve a much larger robot than theoretically necessary.  
As can be seen from the presented overview of related work, collision avoidance of industrial robots is commonly done by changing the layout of the workplace, changing the placement of the robot, changing the trajectory during programming, or path-planning, but not by changing the shape of the robot itself.  
The biggest fields of related research are soft robots and continuum robots. This is, however, a different topic--these systems can change the kinematic structure and shape drastically, even during operation, and the shape changing can be the source of the technological movement (typical for some inflatable robots). These robots are not rigid enough for tasks meant for an industrial robot.  
Manual modification of the shape of some parts of a robotic arm, as described in ([PERSON] et al., 2017; [PERSON] et al., 2018; [PERSON] et al., 2018), is close to our research, but these arms have some stiffness issues and can bend uncontrollably at higher loads. Each shape modification also changes the kinematic structure, which makes accurate control quite complicated--as can be seen from the articles focusing on control of continuum robots ([PERSON] et al., 2018; [PERSON] et al., 2018; [PERSON] et al., 2018; [PERSON] et al., 2018). The advantage of such robots is that the shape can be changed as needed without having to manufacture a completely new arm. This advantage can be useful in some situations, especially in service robotics, and can outweigh the disadvantages. In industrial applications, however, the ease of precise and reliable control of the robot is crucial.  
Our novel approach to collision avoidance in a static environment involves the use of a specific type of kinematic structure with six degrees of freedom (typical for commercial robots, as will be explained further) and changing the length and shape of the two main links of the manipulator (the lower and upper arm) while keeping the relative orientation of joints the same--thus also keeping the same type of kinematic structure. As can be seen from the overview of related work, this is an innovative approach, not just a modified method. The aim of this work is to present some possible methods for this approach and to demonstrate its possible use, because a custom-made manipulator could provide better performance parameters than a universal manipulator.  
The custom-shaped arms are supposed to be designed and manufactured in advance for particular tasks, without the ability to be changed later (they can, however, be replaced by differently shaped parts when needed). It is also possible to utilize some of the above-mentioned methods ([PERSON] et al., 2018; [PERSON] et al., 2018) that allow changing of the shape at will.