Towards a More Robust Non-Rigid Robotic Joint

Abstract

The following paper presents an improved, low cost, non-rigid joint that can be used in both robotic manipulators and leg-based traction robotic systems. This joint is an improvement over the previous one presented by the same authors because it is more robust. The design iterations are presented and the final system has been modeled including some nonlinear blocks. A control architecture is proposed that allows compliant control to be used under adverse conditions or in uncontrolled environments. The presented joint is a cost-effective solution that can be used when normal rigid joints are not suitable.

Design, Modeling, and Control of a Single Leg for a Legged-Wheeled Locomotion System with Non-Rigid Joint

“…The only configuration where this joint does not exhibit its vertical absorption capability is when it is fully stretched. This non-rigid joint is the one described in a previously published work [16]. The rigid joint follows the same circular configuration and size; however, it connects directly to the motor shaft.…”

“…[17], preceded by Ref. [16]), it was found to be more convenient to use in-line gearboxes. The used motors were those from CQRobot, being decided to use different gearboxes.…”

“…It is also presented in Table 1, including the components used to build this prototype, as well as their price range. Considering that changing the configuration of just one joint to a complete leg changes the model presented in [16], it was necessary to expand the conceptual representation of each joint. Using these, it becomes possible to obtain the system of equations that follows.…”

“…It is important to state that the used motor model assumes that T q = T m while T m < T q_max , this way explaining the existence of the motor dead zone, which is a nonlinear element of the model. However, despite this, it can be neglected, given that it was proven in [16] that it is almost nonexistent and otherwise it will turn the defined system into a nonlinear one.…”

“…This model originated the following result, which can be compared to the data obtained in the test through the graphic on Figure 7. Another change from the solution proposed in [16] is the control. Bearing in mind the tuning limitations of the previously implemented controllers, which quickly became unstable, it was decided to use a state-space control technique.…”