Dynamic Control of the Bionic Handling Assistant Falkenhahn, Valentin; Hildebrandt, Alexander; Neumann, Rudiger ...
IEEE/ASME transactions on mechatronics,
02/2017, Volume:
22, Issue:
1
Journal Article
Peer reviewed
In the previous decade, multiple approaches for kinematic controllers of continuum manipulators were successfully developed. However, for fast and exact motions of continuum robots that are hardly ...seen so far, dynamic controllers are necessary-especially for spatial manipulators with multiple sections. Therefore, a dynamic controller in actuator space is developed that both exploits input constraints and decouples the actuators in order to provide a good and intuitive dynamic behavior of the manipulator. Having a pneumatically actuated manipulator with multiple actuators, this can be achieved using a cascaded control approach with a centralized actuator length controller and an underlying decoupled pneumatic controller. For both the outer multiple-input multiple-output (MIMO) controller and the inner single-input single-output (SISO) controllers, model-based controllers are developed based on suitable models using feedback linearization and a combination of feedforward control and linear PD-controllers. The resulting actuator controller can be used for tracking optimized trajectories in actuator space and also for possible extensions towards direct tool center point feedback.
Ball screw drives are used in automation applications and machine tools to translate rotational motion of an electric motor into translational motion of a slide. Their frequency responses show ...characteristic torsional and translational resonances. The resonance frequencies vary with the slide position, which is due to the distributed stiffness and inertia of the flexible ball screw. The proposed model treats the ball screw as a flexible element, using Ritz series expansions to obtain a finite approximation of the continuous deformations. The use of problem-specific basis functions allows for a low-order approximation, making the model especially well suited for control design. The model shows excellent validation results and reproduces the variation of the resonance frequencies with high accuracy.
Soft robotics research has rapidly incorporated Additive Manufacturing (AM) into its standard prototyping repertoire. While numerous publications have highlighted the suitability of AM for producing ...soft pneumatic actuators, fluidic components, and lightweight structures, their integration into an industry-like robotic arm has not yet been shown. Against this background, a pneumatically actuated robot was developed that incorporates additively manufactured soft structures into rigid articulated hinges that generally allow for integration into today’s industrial production lines. The development of the robot, including pneumatic soft rotary bellows and rotary vane actuators (RVAs), is summarized, and its functionality is proven. It was found that using AM can increase the structural stiffness of robot links to a significant degree as manufacturing-related constraints in topology optimization are largely eliminated. Moreover, it was found that multi-material polyjet printing of soft rotary bellows actuators allows for highly integrated designs that provide low leakage and friction. However, these soft rotary actuators are still inferior in terms of endurance and performance if compared to AM replicas of RVAs. Our work narrows the gap between soft robotics research and today’s industrial applications, may realign research directions, and may provide impulses for the industry towards soft robotics and AM.
Despite an emerging interest in soft and rigid pneumatic lightweight robots, the pneumatic rotary actuators available to date either are unsuitable for servo pneumatic applications or provide a ...limited angular range. This study describes the functional principle, design, and manufacturing of a servo pneumatic rotary actuator that is suitable for continuous rotary motion and positioning. It contains nine radially arranged linear bellows actuators with rollers that push forward a cam profile. Proportional valves and a rotary encoder are used to control the bellows pressures in relation to the rotation angle. Introducing freely programmable servo pneumatic commutation increases versatility and allows the number of mechanical components to be reduced in comparison to state-of-the-art designs. The actuator presented is designed to be manufacturable using a combination of standard components, selective laser sintering, elastomer molding with novel multi-part cores and basic tools. Having a diameter of 110 mm and a width of 41 mm, our prototype weighs less than 500 g, produces a torque of 0.53 Nm at 1 bar pressure and a static positioning accuracy of 0.31° with no limit of angular motion. By providing a description of design, basic kinematic equations, manufacturing techniques, and a proof of concept, we enable the reader to envision and explore future applications.
State-of-the-art Additive Manufacturing processes such as three-dimensional (3D) inkjet printing are capable of producing geometrically complex multi-material components with integrated elastomeric ...features. Researchers and engineers seeking to exploit these capabilities must handle the complex mechanical behavior of inkjet-printed elastomers and expect a lack of suitable design examples. We address these obstacles using a pneumatic actuator as an application case. First, an inkjet-printable actuator design with elastomeric bellows structures is presented. While soft robotics research has brought forward several examples of inkjet-printed linear and bending bellows actuators, the rotary actuator described here advances into the still unexplored field of additively manufactured pneumatic lightweight robots with articulated joints. Second, we demonstrate that the complex structural behavior of the actuator’s elastomeric bellows structure can be predicted by Finite Element (FE) simulation. To this end, a suitable hyperviscoelastic material model was calibrated and compared to recently published models in a multiaxial-state-of-stress relaxation experiment. To verify the material model, Finite Element simulations of the actuator’s deformation behavior were conducted, and the results compared to those of corresponding experiments. The simulations presented here advance the materials science of inkjet-printed elastomers by demonstrating use of a hyperviscoelastic material model for estimating the deformation behavior of a prototypic robotic component. The results obtained contribute to the long-term goal of additively manufactured and pneumatically actuated lightweight robots.
Purpose
This study aims to investigate the suitability of a multi-step prototyping strategy for producing pneumatic rotary vane actuators (RVAs) for the development of lightweight robots and ...actuation systems.
Design/methodology/approach
RVAs typically have cast aluminum housings and injection-molded seals that consist of hard thermoplastic cores and soft elastomeric overmolds. Using a combination of additive manufacturing (AM), computer numerical control (CNC) machining and elastomer molding, a conventionally manufactured standard RVA was replicated. The standard housing design was modified, and polymeric replicas were obtained by selective laser sintering (SLS) or PolyJet (PJ) printing and subsequent CNC milling. Using laser-sintered molds, actuator seals were replicated by overmolding laser-sintered polyamide cores with silicone (SIL) and polyurethane (PU) elastomers. The replica RVAs were subjected to a series of leakage, friction and durability experiments.
Findings
The AM-based prototyping strategy described is suitable for producing functional and reliable RVAs for research and product development. In a representative durability experiment, the RVAs in this study endured between 40,000 and 1,000,000 load cycles. Frictional torques were around 0.5 Nm, which is 10% of the theoretical torque at 6 bar and comparable to that of the standard RVA. Models and parameters are provided for describing the velocity-dependent frictional torque. Leakage experiments at 10,000 load cycles and 6 bar differential pressure showed that PJ housings exhibit lower leakage values (6.8 L/min) than laser-sintered housings (15.2 L/min), and PU seals exhibit lower values (8.0 l/min) than SIL seals (14.0 L/min). Combining PU seals with PJ housings led to an initial leakage of 0.4 L/min, which increased to only 1.2 L/min after 10,000 load cycles. Overall, the PU material used was more difficult to process but also more abrasion- and tear-resistant than the SIL elastomer.
Research limitations/implications
More work is needed to understand individual cause–effect relationships between specific design features and system behavior.
Originality/value
To date, pneumatic RVAs have been manufactured by large-scale production technologies. The absence of suitable prototyping strategies has limited the available range to fixed sizes and has thus complicated the use of RVAs in research and product development. This paper proves that functional pneumatic RVAs can be produced by using more accessible manufacturing technologies and provides the tools for prototyping of application-specific RVAs.
Fast and exact motions of continuum robots are hardly seen so far. Partly this is caused by physical constraints, e.g. small available actuation forces. Another reason is the dynamic coupling between ...the actuators that cannot be neglected during fast motions. Therefore, a model-based MIMO controller in actuator space was developed, that is based on a spatial dynamic model with one mass point per section. Using feedback linearization, the actuators can be decoupled and feedforward control in combination with linear controllers can be applied. Measurements of an example manipulator show the good tracking result of pure feedforward action with feedback linearization. Adding a linear PD-controller increases the robustness against disturbances without reducing the possibility of fast motions.
Servopneumatic actuators are very attractive for automated handling tasks or robot operations. They have many advantages such as high speed, high robustness in rough manufacturing environment or high ...power-to-weight ratio. The considered actuator system is a standard configuration in pneumatics consisting of a double acting pneumatic cylinder controlled by a proportional directional control valve. For the set-up a detailed mathematical model is derived. In order to guarantee an accurate tracking behaviour, a model-based nonlinear controller is presented. Model based approaches for the control design have several advantages. Tuning of the controller can be reached in a systematic way even in the case of a large variety of different configurations. But not only the control design itself can be treated. The model offers the possibility to optimize the size of components for demanded automation tasks. In most cases, this is solved based on steady state assumptions. In this contribution, a method for a design procedure for the pneumatic actuator system based on the dynamic equation is presented. With the representation of the system, an optimization procedure for the components is introduced. The optimization criteria consist of the minimization of the air consumption and investment costs.
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