Decoupled Control for the Bicycling UGent Knee Rig: Design, Implementation, and Validation

Abstract

Abstract-This paper presents the design and implementation of a new control strategy for Ghent University, Ghent, Belgium (UGent) knee rig, which is capable of imposing bicycle motions on cadaver knee specimens in order to investigate knee biomechanics and the impact of newly designed knee implants. An electromechanical description of the system with its instrumentation and limitations is given. Via system identification, a dynamical model of the multipleinput/multiple-output system is obtained on which the control strategy design is based. This control strategy combines position control and force control. Dynamical analysis of the system suggests the need for a Proportional-IntegralDerivative (PID) control strategy with gain adaptation. In order to fulfill the performance specifications, a feed-forward action and decouplers are added to the control strategy, and their advantages are shown via simulations and experiments. The complete strategy is implemented on the real system and the output signals are measured for analysis. The results indicate that the identified model fits well to the measured data and that the designed control strategy is able to accurately control the system. The measurements show that the predefined performance specifications have been achieved for a bicycle motion with a period of 10 s; the error on the position is smaller than 2 mm and the error on the force is smaller than 10 N.

Ground Reaction Force Control in the UGent Knee Rig

“…For a more detailed biomechanical description, the readers are referred to [7]. Control of the ankle position, quadriceps and hamstring forces has been presented in [8]. In [8] no attention was paid to the ground reaction forces.…”

“…Control of the ankle position, quadriceps and hamstring forces has been presented in [8]. In [8] no attention was paid to the ground reaction forces. Here this extension is made as it is of crucial importance for comparison with literature.…”

“…This makes the 'interoperability' and 'reusability' of FAIR data a challenge as comparison of data from different rigs is difficult. Mitigation of this problem for the UGent Knee Rig (UGKR) [7], [8] is the focus of this work.…”

“…The disadvantage here is that the tibia always remains in the vertical direction limiting the flexibility. The UGKR has been developed to wider even further the range of motion of the OKR while respecting the basic principle of applying loading conditions to the muscles [7], [8]. In [8], it is shown that the UGKR is capable of imposing controlled bicycle motions onto knee specimen using a decoupled control strategy.…”

“…The UGKR has been developed to wider even further the range of motion of the OKR while respecting the basic principle of applying loading conditions to the muscles [7], [8]. In [8], it is shown that the UGKR is capable of imposing controlled bicycle motions onto knee specimen using a decoupled control strategy. The UGKR applies a quadriceps and hamstring force and provides ankle motion in the sagittal plane, i.e.…”