A New Kinematic Model and Control Strategy for a Mobile Platform for Transporting Lightweight Manipulators

Abstract

This work is concerned with the mechanical design and the description of the different components of a new mobile base for a lightweight mobile manipulator. These kinds of mobile manipulators are normally composed of multiple lightweight links mounted on a mobile platform. This work is focused on the description of the mobile platform, the development of a new kinematic model and the design of a control strategy for the system. The proposed kinematic model and control strategy are validated by means of experimentation using the real prototype. The workspace of the system is also defined.Electronics 2018, 7, 441 2 of 27 were, initially, outside their workspace. Some works about the analysis and design of lightweight manipulators mounted on mobile platforms can be found in [5,6], and about trajectory planning of these systems in [7].Many existing applications take advantage of using arms with lightweight links mounted on mobile platforms. Some of these are: intervention robots, robots used to clean up hazardous waste, for bomb disposal and refighting, the maintenance of dangerous items (e.g., hot electric power lines), or mining robots. For example, Ref.[8] presents a robot to assist humanitarian demining and [9] a design of an automatic system for aircraft painting.In the context of a multiple large link manipulators mounted on a mobile platform, the movement of the links will reduce the physical stability of the system, increasing the possibilities of overturning of the mobile platform. When the mass of the flexible manipulator is important in comparison with the overall mass of the mobile platform, the center of mass is shifted from the base of the robot. This reduces the maximum speed and the maximum terrain inclination in which the robot can navigate and the maneuvers that the manipulator can perform without leading the center of mass out of the support polygon, finally causing the overturning of the robot. For that reason, four legs have been added to the mobile platform in order to increase the polygon support of the system and increase considerably the physical stability of the system.In this work, a mechanical device capable of transporting large lightweight manipulators is presented. Its main objectives are: (a) transport the manipulator, (b) increase the stability of the system when it reaches a specific target and (c) help in the positioning of the tip of the manipulator. The innovations introduced in our mechanism over previous designs are related to the inclusion of the four controlled legs in the mobile platform: (1) These four legs enlarge the stability polygon, preventing the overturn of the platform in the case that the large lightweight arm placed on it leans excessively. This approach to increase the robot stability has not been done before in this context. (2) Controlling these legs and, by means of them, the inclination of the platform, allows us to accurately position the tip of the manipulator. These positioning movements are of a reduced range, but, since large movements and approximate pos...

Vibration control of very large and lightweight structures mounted on a four-legged platform

“…On the other hand, the platform is a mobile base with rectangular shape, four actuated legs and four wheels (see Figure 1). The dimensions of the platform can be found in Feliu-Talegon et al (2018).

Figure 1.(a) Real prototype, (b) Hardware components.

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“…The combination of movements of the four legs allows us to modify the pose of the platform and, therefore, the pose of the end-effector of the large structure where the camera is located. More information about this platform can be found in Feliu-Talegon et al (2018).…”

“…This model allows us to obtain the orientation, θ , ϕ , and the posture of the system, z , in function of the extension of 3 linear actuators that are in contact with the ground (di1, di2, and di3). Detailed information about the kinematic model and the associated frames can be found in Feliu-Talegon et al (2018).…”

“…Then, only these three linear actuators are needed to control the system. The remaining leg is considered as a passive leg which is used to make the system more stable, thus avoiding imbalance as it was done in Feliu-Talegon et al (2018). We propose to obtain the desired position of the linear actuator (di4) by meeting the condition that the passive leg must be in contact with the ground which is similar to (2), as follows…”

“…The 4th leg is used to form a stability polygon of 4 vertices. The kinematics, end effector pose control, and robot workspace assuming that a rigid link has been mounted were given in our previous work Feliu-Talegon et al (2018).…”