Straight leg walking strategy for torque-controlled humanoid robots

Hong

Int. J. Control Autom. Syst.

2021

We propose a bipedal walking and impact reduction algorithm for a bipedal robot with pneumatically driven knees. The proposed algorithm is meaningful in that unlike in the existing studies on fully pneumatically driven robots and their control, it can overcome the low control performance of pneumatic actuators while utilizing the high compliance of pneumatic actuators through the high control performance of other joints in robots that apply pneumatic actuators only to the knee joint. Our algorithm takes advantage of whole-body control to overcome the low control performance of pneumatic systems and utilizes pneumatic compliance by simultaneously controlling the force and stiffness of the pneumatic actuators. Since a pneumatic actuator outputs a force, a force and torque converter is added to the general whole-body control framework, and a torque limit is considered as a function of the joint angle. In addition, a mechanism for selecting the stiffness of the knee is added. In particular, a force control method based on maintaining the minimum stiffness is applied to reduce the impact force when the ground conditions suddenly change. The pneumatics and the robot system were accurately modeled in a simulation, and the proposed algorithm was applied in the simulation to realize bipedal walking and to confirm the impact reduction effect in the event of a sudden ground condition change.

Section: Whole-body Control Frameworkmentioning

confidence: 99%

Bipedal Walking and Impact Reduction Algorithm for a Robot with Pneumatically Driven Knees

Hong

Int. J. Control Autom. Syst.

2021

2018 IEEE International Conference on Robotics and Automation (ICRA)

“…As discussed in [15], by allowing the CoM height to vary, the CMP deviates from the nominal eCMP location. From the perspective of the ICP, height variations from the nominal height z nom = ω 2 /g will cause the CMP to deviate from the eCMP, with a relationship defined by…”

Section: A Walking Controlmentioning

confidence: 99%

“…We propose directly address the objective of straightening the legs by biasing the whole-body controller solutions towards those that straighten the legs as much as possible, rather than through setting a desired CoM height. As noted in [15], the whole-body controller can resolve the kinematic and dynamic constraints on the system at run time. To accomplish this, we propose underconstraining the whole-body controller by not specifying a desired force in the vertical direction.…”

Section: Introductionmentioning

confidence: 99%

Straight-Leg Walking Through Underconstrained Whole-Body Control

Griffin

Wiedebach

Bertrand

et al. 2018

We present an approach for achieving a natural, efficient gait on bipedal robots using straightened legs and toe-off. Our algorithm avoids complex height planning by allowing a whole-body controller to determine the straightest possible leg configuration at run-time. The controller solutions are biased towards a straight leg configuration by projecting leg joint angle objectives into the null-space of the other quadratic program motion objectives. To allow the legs to remain straight throughout the gait, toe-off was utilized to increase the kinematic reachability of the legs. The toe-off motion is achieved through underconstraining the foot position, allowing it to emerge naturally. We applied this approach of under-specifying the motion objectives to the Atlas humanoid, allowing it to walk over a variety of terrain. We present both experimental and simulation results and discuss performance limitations and potential improvements.

2018 IEEE-RAS 18th International Conference on Humanoid Robots (Humanoids)

“…Besides, another effective way of energy saving is the use of the body vertical motion (CoM height variation, CoMHV), which has been demonstrated in [23] and [24]. Recent years have also seen efforts in bipedal walking with time-varying CoM height or straight leg [25], [26]. Using the CoMHV approach, above works qualitatively analyzed the energy efficiency (evaluated with the amount of torque input required by the knee joint).…”

Section: Total Energy Consumptionmentioning

confidence: 99%

Energy-Efficient Bipedal Gait Pattern Generation via CoM Acceleration Optimization

Ding

Zhou

Xiao

2018

Self Cite

Energy consumption for bipedal walking plays a central role for a humanoid robot with limited battery capacity. Studies have revealed that exploiting the allowable Zero Moment Point region (AZR) and Center of Mass (CoM) height variation (CoMHV) are strategies capable of improving energy performance. In general, energetic cost is evaluated by integrating the electric power of multi joints. However, this Joint-Power-based Index requires computing joint torques and velocities in advance, which usually requires time-consuming iterative procedures, especially for multi-joints robots. In this work, we propose a CoM-Acceleration-based Optimal Index (CAOI) to synthesize an energetically efficient CoM trajectory. The proposed method is based on the Linear Inverted Pendulum Model, whose energetic cost can be easily measured by the input energy required for driving the point mass to track a reference trajectory. We characterize the CoM motion for a single walking cycle and define its energetic cost as Unit Energy Consumption. Based on the CAOI, an analytic solution for CoM trajectory generation is provided. Hardware experiments demonstrated the computational efficiency of the proposed approach and the energetic benefits of exploiting AZR and CoMHV strategies.