Experimental analysis of Type II singularities and assembly change points in a 3UPS+RPU parallel robot

Pulloquinga, José L.; Mata, Vicente; Valera, Ángel; Zamora-Ortiz, Pau; Díaz‐Rodríguez, Miguel; Zambrano, Iván

doi:10.1016/j.mechmachtheory.2020.104242

Cited by 18 publications

(10 citation statements)

References 38 publications

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“…At the same time, we try to combine the fuzzy control strategy to adjust the switching gain of the manipulator control, so as to alleviate the chattering problem encountered in the controller design process and improve the overall performance of the controller. In the case of a certain unknown model error and external disturbance, a trajectory tracking test of the serial robot is designed to verify the robustness of the control algorithm and the fast error convergence characteristics [22][23][24].…”

Section: Related Workmentioning

confidence: 99%

Trajectory Control Algorithm of Flexible Joint Manipulator Based on Random Matrix and Screw Theory

Guo

Da-shuai

2022

Mathematical Problems in Engineering

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Flexible articulated manipulators are often used for the task of tracking reference trajectories in space and have attracted much attention. Aiming at the uncertainty of the robot system, based on random matrix and screw theory, this paper constructs a trajectory control model of a flexible joint manipulator. In order to reduce the steady-state tracking error, a random matrix variable structure control method is introduced into the model, and a nonlinear spinor-like random matrix function is designed to improve the traditional random matrix surface. In the simulation process, the dynamic model of the series robot is firstly obtained according to the screw and random matrix equation, and the dynamic characteristics are analyzed. Combined with dynamic surface control technology, a neural network controller is designed to solve the problem of dimensional explosion and ensure that the tracking error converges to a small neighborhood of zero. The experimental results show that by using the observation value to replace the unmeasurable state of the system, combining it with the random matrix network to identify the unknown dynamics of the system, and designing the random matrix network controller, the tracking control of the system can be realized, and the tracking error can be ensured to converge to a small neighborhood of zero. The control system has a better control effect than traditional PID, the peak time is shortened by 45.83%, the adjustment time is shortened by 46.91%, the maximum overshoot is reduced by 51.35%, and the steady-state error after filtering is only 0.049, which is reduced by 47.31%. Effective interference signal and measurement noise are suppressed, and the quantitative observation performance of the flexible joint manipulator system is improved.

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Section: Related Workmentioning

confidence: 99%

Trajectory Control Algorithm of Flexible Joint Manipulator Based on Random Matrix and Screw Theory

Guo

Da-shuai

2022

Mathematical Problems in Engineering

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“…where → z is the unit vector of the forces applied by the actuators, and → r is the position vector for the connection point of the limbs with the mobile platform measured from O m ; see Figure 2. The capability to detect the proximity to a type II singularity given by the six Ω i,j indices defined in Equation ( 7) has been verified from an analytical and experimental perspective [19]. However, the capability to identify the pair of limbs responsible for the type II singularity has not been exploited.…”

Section: Angle Between Two Output Twist Screwsmentioning

confidence: 99%

“…The main objective of the simulation is to test that the novel hybrid controller increases the values of J D and Ω i,j in the vicinity of a type II singular configuration; i.e., it is able to release the PR under study from the type II singularity. Since the 3UPS+RPU PR was built to interact with human knees, it is used to execute three rehabilitation movements: flexion of the hip, flexion-extension of the knee, and internal-external rotation of the knee [19]. This study, combining these three fundamental movements for simulation and experimentation, performs five knee rehabilitation trajectories ending in a type II singular configuration (see Table 3).…”

Section: Simulation Of the Vision-based Hybrid Controllermentioning

confidence: 99%

“…Subsequently, Wang et al [18] using the TI proposed by Takeda and Funabashi established that for a type II singularity, at least two OTSs are linearly dependent. Pulloquinga et al [19] proposed the angle between two instantaneous screw axes from the OTSs (Ω) as a measure for the proximity detection of type II singularities, providing physical meaning and the capability to determine the chains producing the singular configuration.…”

Section: Introductionmentioning

confidence: 99%

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Vision-Based Hybrid Controller to Release a 4-DOF Parallel Robot from a Type II Singularity

Pulloquinga

Escarabajal

Ferrándiz

et al. 2021

Sensors

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The high accuracy and dynamic performance of parallel robots (PRs) make them suitable to ensure safe operation in human–robot interaction. However, these advantages come at the expense of a reduced workspace and the possible appearance of type II singularities. The latter is due to the loss of control of the PR and requires further analysis to keep the stiffness of the PR even after a singular configuration is reached. All or a subset of the limbs could be responsible for a type II singularity, and they can be detected by using the angle between two output twist screws (OTSs). However, this angle has not been applied in control because it requires an accurate measure of the pose of the PR. This paper proposes a new hybrid controller to release a 4-DOF PR from a type II singularity based on a real time vision system. The vision system data are used to automatically readapt the configuration of the PR by moving the limbs identified by the angle between two OTSs. This controller is intended for a knee rehabilitation PR, and the results show how this release is accomplished with smooth controlled movements where the patient’s safety is not compromised.

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“…However, this is not enough to ensure a complete singular-free workspace and so the singularity analysis is still a concern. The characterization of Type II singularities has also been researched, and methods based on Screw Theory [15] have been proposed [16]- [18] since the Jacobian alone does not provide enough physical information. Some works have been developed using these kinds of techniques to help a PR deal with singularities during operation, requiring extra sensorization such as vision systems since the robot's kinematic model is no longer valid in the vicinity of a singularity [19].…”

Section: Introductionmentioning

confidence: 99%

Combined Admittance Control With Type II Singularity Evasion for Parallel Robots Using Dynamic Movement Primitives

Escarabajal¹,

Pulloquinga²,

Valera³

et al. 2023

IEEE Trans. Robot.

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This paper addresses a new way of generating compliant trajectories for control using movement primitives to allow physical human-robot interaction where parallel robots (PRs) are involved. PRs are suitable for tasks requiring precision and performance because of their robust behavior. However, two fundamental issues must be resolved to ensure safe operation: i) the force exerted on the human must be controlled and limited, and ii) Type II singularities should be avoided to keep complete control of the robot. We offer a unified solution under the Dynamic Movement Primitives (DMP) framework to tackle both tasks simultaneously. DMPs are used to get an abstract representation for movement generation and are involved in broad areas such as imitation learning and movement recognition. For force control, we design an admittance controller intrinsically defined within the DMP structure, and subsequently, the Type II singularity evasion layer is added to the system. Both the admittance controller and the evader exploit the dynamic behavior of the DMP and its properties related to invariance and temporal coupling, and the whole system is deployed in a real PR meant for knee rehabilitation. The results show the capability of the system to perform safe rehabilitation exercises.

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Experimental analysis of Type II singularities and assembly change points in a 3UPS+RPU parallel robot

Cited by 18 publications

References 38 publications

Trajectory Control Algorithm of Flexible Joint Manipulator Based on Random Matrix and Screw Theory

Trajectory Control Algorithm of Flexible Joint Manipulator Based on Random Matrix and Screw Theory

Vision-Based Hybrid Controller to Release a 4-DOF Parallel Robot from a Type II Singularity

Combined Admittance Control With Type II Singularity Evasion for Parallel Robots Using Dynamic Movement Primitives

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