## 3 Literature Review on Manipulator Design and Optimization Methods
### Topology Optimization and Detailed Analysis of Manipulator Loads  
Many publications touch on the subject of load selection for optimization purposes. Most often, the process is carried out on examples of industrial manipulators. In [21], the authors performed topological optimization of an industrial manipulator arm, taking into consideration the variability of the load direction during arm rotation. The authors assumed that the arm is loaded at the end with a vertical force. The optimization performed takes into account the loads present when the arm is rotated from an angle of 0 to 170, with 10-degree resolution. In [22], the authors dealt with minimizing the mass of an industrial manipulator arm using topological optimization. The authors proposed methods to take into account multiple loading conditions in density topological optimization by introducing weighted sums of material densities obtained for different loading cases. In [21; 23], the authors proposed a method to solve a similarly defined problem based on the processing of the resulting topology created by superposing solutions for individual load angles. There are also publications where authors perform more advanced analysis on the subject of load selection for optimization purposes, often illustrated by examples involving industrial manipulators. In [21], a topological optimization of an industrial manipulator arm was performed under varying load directions during arm rotation. The researchers assumed a vertical force acting at the arm's end, and accounted for rotations from 0 to 170 degrees in 10-degree increments. In [22], the same group aimed to minimize the mass of an industrial manipulator arm using topology optimization. They proposed methods to handle multiple loading conditions by introducing weighted sums of material densities obtained for different load cases. Finally, in [21; 23], the authors addressed a similarly defined problem by processing the final topology generated through superimposing solutions for individual load angles. This approach highlights how combining results from multiple load configurations can yield a more robust design. The work presented in [24] involved topological optimization of upper-limb exoskeleton components using two methods. The authors performed optimization for a single configuration, for which the structure stress values were the highest. It was assumed that the arms were straightened horizontally and the maximum accelerations achievable by the arm joints were assumed as loads. In [25], the authors presented the process of designing a manipulator with a parallel structure intended for palletizing. To assume the loads for topological optimization, they analyzed the loads in individual manipulator joints for the full range of movement of the members for the assumed transferred weight. The authors adopted one selected load condition for optimization. In [26], the authors presented a method for optimizing a lightweight anthropomorphic manipulator. Typical configurations and loading conditions were analyzed to identify loads on the arm. Various loads were used to optimize the components. Each load case was divided into bending, shear and tension loads. In [19], the authors presented a method for optimizing a manipulator intended for spray painting, using topological and parametric optimization. The calculations used load cases that generated the largest effector deflection for 30 randomly generated manipulator configurations. The deflections were calculated via the FEM using the model before optimization. Analysis of optimization methods--particularly topology optimization--applied to designing portable robot manipulators for special tasks has shown that existing approaches from the literature cannot be directly used. This limitation arises from the distinct parameters and functionalities of such manipulators. For example, because these robots are operated manually, structural stiffness and joint clearances have a lesser impact on movement precision.