Variable stiffness structural design of a dual-segment continuum with independent stiffness and angular position

Abstract

• This paper studies the challenging problem of variable stiffness for a class of multisegment continuum manipulators with pneumatically actuated modular mechanisms. The main contributions of this paper are summarized as follows. • Following our previous work on the single-segment continuum manipulator [15] , we present a dual-segment continuum manipulator composed of a leading unit and a follower unit. By means of the pressure variation of the PMAs in each unit, the independent unit locking can be guaranteed in the sense that no auxiliary structures, such as nonlinear springs [36] , [37] , [38] or locking devices [39] , [40] , [41] , are employed. • We propose a stiffness model for a class of pneumatically actuated continuum manipulators that include couplings and interconnections between the parallel and serial arranged PMAs. This model exhibits the relationship between the stiffness of each unit and the inflation pressure of PMAs such that the computational burden needed in other works [ 15 , 16 , 17 , 45 , 46 , 48 , 49 , 56 , 57 , 61 , 62 ] is eliminated. • Unlike the existing multisegment manipulators that are limited by the coupling of the angular position and stiffness [ 23 , 24 , 25 , 42 , 56 , 57 , 63 ], as well as the complex configuration in each modular mechanism [58] , [59] , [60] , the presented dual-segment continuum manipulator allows the stiffness to be changed independently of the angular position via utilizing a simple design with only one actuator type (i.e., the PMA). This paper investigates the problem of the variable stiffness for a class of multisegment continuum manipulators. A simple design that mainly consists of two types of pneumatic muscle actuators (PMAs) is introduced to deal with the problem. To provide a detailed analysis, this characteristic of the variable stiffness is coupled with a mathematical analysis that is built upon the geometric mechanics and the performance testing of the stiffness in each PMA, thereby forming the stiffness model. Moreover, utilizing the simple design enables the continuum manipulator composed of two units to vary its stiffness independently from the angular position. In addition, using only the pressure variation of the PMAs in each unit, the dual-segment manipulator also has the capacity to implement independent unit locking. The experimental results further validate the expected performance of the proposed continuum manipulator.