Create a 6-DOF modular robot configuration from a modular robotic system. As shown in Fig. 2.53, the modular robotic system consists of standardized modules including rotary joints, linear joints, links, wrists, and grippers (Bi et al. 2008).
As shown in Fig. 2.54, three critical design issues are involved in the application of a reconfigurable system. These design issues are architecture design, configuration design, and control design.
Architecture design determines the types of system modules and the connections of system modules. Modules in a reconfigurable system are encapsulated; in other words, the internal implementation of a module does not affect the interfaces of the module with others. The connections of a module are the options by which the module can be interacted with others. The design of system architecture aims to produce as many system configurations as possible with a given set of modules. Note that different configurations can be used to fulfill different tasks; the more configurations a system can generate, the better capabilities of the reconfigurable system can deal with changes and uncertainties in a dynamic environment. Architecture design is involved at the phase of reconfigurable system design. In configuration design, it is assumed that the reconfigurable system is given; for example, the types and the numbers of robotic modules in Fig. 2.52 are given. Configuration design is to select a set of modules and configure modules into a robot to fulfill the functional requirements of a given task optimally. Configuration design is involved at the phase of system application. Active modules in a reconfigurable system have their local controls; however, there are system-level goals when modules are assembled into a robot.
Therefore, control design is to coordinate system modules, so that these modules can collaborate with each other to fulfill given tasks satisfactorily. The control design is involved at the phase of system operation (Bi et al. 2008).
Since the problem does not specify the functional requirements of the 6-DOF robot in terms of the workload, trajectory, velocity, and acceleration of toolpath, arbitrary three 1-DO joints are selected to build a 6-DOF model. As shown Fig. 2.53, the demonstrated robot has 6 DOF; it consists of 1 R-90 rotary joint, 1 L-70 linear joint, 2 R-70 rotary joints, 1 W-70 wrist, 1 link module for the connection of R-90 and L-70 modules, and 1 angled link module for the connection of L-70 and R-70.
Note that a W-70 has 2 DOF. In the robot assembly, each active module has one or 2 DOF which are driven by respective motors (Fig. 2.55). In a top down assembly method, parts and components are created during the course of assembly modeling. The details of part models are not available when the assembly relations are defined, and constitutive parts or components are created one by one based on the conceptualized structure and assembly relations of products.
Note that even though parts are created during the course of assembly modeling, they can be saved, either internally or externally, as individual models. Top-down modeling allows engineers to utilize geometric relations and constraints in the high-level structure for newly created parts. In such a way, geometric modeling and assembly modeling can be proceeded simultaneously. Engineers can view the assembly relations of the part when the part is modeled.
A top-down method reduces the rework when the assembly relations are changed in a product design since the derived parts are associated with the assembly constraints when they are modeled. Therefore, top-down modeling is very useful at the concep- tual design stage; it is widely used in tooling design since the geometries and spatial arrangement of tooling depend on the parts to be manufactured. In practice, a top- down method can be used to create an assembly model partially, i.e., a few critical parts in assembly or some key features of parts. Engineers can use the top-down modeling method to layout an assembly including key parts customized to assembly relations (Dassault Systems 2020).