Development of a parallel manipulator for force display

It is important to know the inter-atomic bonding state in material for a new material design and analysis. Although the bonding states can be simulated based on the inter-atomic potential, it is difficult to understand them immediately in three-dimensional space. To understand the inter-atomic bonding state intuitively, it is effective to use force display systems. A high-performance force display system for material science is then developed. The force display consists of a parallel mechanism with direct-drive linear servo actuators. The mechanism is called a fixed linear type parallel mechanism. Since the actuators are fixed on the base, high-speed motion of the manipulator is possible, and the mechanism has a high load capacity and back drivability. These characteristics lead to a high-performance force feedback control. In the current paper, the design and prototyping are described. In addition, it is applied for the force display experiment of inter-atomic bonding state, and the effectiveness is demonstrated.

Robogami structures are employed for many purposes, including miniature parallel manipulators. Parallel manipulators require accurate joint position feedback, underlining the open problem in robogami structures for providing sophisticated feedback with 2D, fully embeddable, down-scalable, flexible sensors. Existing studies include only on-off control applications, excluding any parallel mechanism implementations and continuous proportional control signals. We implement silver inkjet printed angle sensors for the first time into a robogami structure and use this class of sensors for control. For the first time, a parallel manipulator is controlled with a 2D sensor, and printed sensors are tested for continuous control. Performances are analyzed with set-point and tracking control tasks using a paper Delta mechanism, compared with on-off control and encoder feedback control cases for better evaluation. A detailed comparison with the existing studies both for robogami parallel mechanisms and other sensor-embedded flexible hinges is provided. Encoder-like control performances are achieved in a wide range of the joint space and down to ~1 mm. RMS task space accuracy is recorded. Sources and potential improvements for the less accurate regions are stated. We conclude that printed sensors are promising for parallel mechanisms and continuous signal control applications.

Zeroing dynamics (ZD), as a powerful method proposed for time-varying problems solving, has found successful applications in motion control of serial manipulators. Compared with serial manipulators, parallel manipulators possess some attractive advantages such as high carrying capacity and high operation accuracy. However, the inherent differences between parallel and serial manipulators set great difficulties on the applications of ZD to the control of parallel manipulators. Making progress along this direction, the first ZD based motion controller of parallel manipulators is proposed and the design procedure of the ZD based scheme is presented. As a typical application, the proposed scheme is utilised to control a Stewart platform for tracking a quatrefoil-shaped path, which illustrates the effectiveness of the ZD based scheme.

The unifying idea for most model-based control approaches for parallel mechanism is to derive a minimal-order dynamics model of the system and then design the corresponding controller. The problem with such a control approach is that the controller needs to change its structure whenever the mechanical system changes its number of degrees-of-freedom. This paper presents a projection-based control scheme for parallel mechanism that works whether the system is overactuated or not; it does not require derivation of the minimal-order dynamics model. Since the dimension of the projection matrix is fixed, the projection-based controller does not need to change its structure whenever the mechanical system changes its number of degrees-of-freedom. The controller also allows to specify lower and upper bounds on the actuator forces/torques, making it suitable not only for the control of parallel manipulators with limited force/torque capability of the actuators but also for backlash-free control of parallel manipulators as well as for control of tendon driven parallel manipulators. The stability of the projection-based controllers is rigourously proved, while the condition for the controllability of parallel manipulators is also derived in detail. Finally, experimental results obtained from a simple parallel mechanism, which changes its degrees-of-freedom, are appended. The results also demonstrate that the maximum actuator torque can be reduced by 20% if the actuator saturation is taken into account by the controller.

In this work, we focus on the design and analysis of a new modular hybrid parallel-serial manipulator for robotised deburring of large jet engine components such as the fan, compressor, and turbine discs. The manipulator consists of a 3-DOF (degree-of-freedom) planar parallel platform and a 3-DOF serial robotic arm. Benefiting from the hybrid kinematic structure, the manipulator exhibits good performance inherited from both serial and parallel robots, e.g. larger workspace and higher dexterity (comparing to a parallel robot), and higher rigidity and higher loading capacity (comparing to a serial robot). Such features are ideal for deburring applications of large jet-engine components. In order to rapidly deploy a demonstration system, the modularity design concept is employed in the system development, which is able to reduce the complexity of the overall design problem to a manageable level. Based on the specific hybrid manipulator design, closed-form symbolic solutions are derived for both forward and inverse displacement analysis. Computation examples are provided to verify the proposed displacement analysis algorithms. To obtain the relationship between the end-effector’s velocity and the active-joint rates, the instantaneous kinematics model of this hybrid manipulator is formulated. These analysis algorithms are essential for the design optimisation, trajectory planning, computer simulation, and real-time control of this hybrid manipulator. Utilising the 6-DOF hybrid parallel-serial manipulator, a robotised deburring system is investigated for large jet-engine components.

Assembling large, heavy space segments presents a significant challenge in aerospace engine production. Rigid collisions often occur during the docking process, impacting the precision and quality of engine assembly. Traditional manual docking depends on workers’ experience to prevent collisions, but it is labor-intensive and low in productivity, making it impractical. Parallel robots, known for their high precision and heavy load capacity, are widely used in precision assembly under heavy load conditions. Therefore, automated docking methods using parallel robots capable of avoiding rigid collisions have emerged as an excellent solution to these issues. This paper presents a framework for easy implementation in practical production. The Stewart parallel robot facilitates automatic docking of heavy aerospace components without rigid collisions. Fractional-order variable damping admittance control is proposed, allowing the robot to dynamically adjust the assembly trajectory based on real-time interaction forces, thus preventing rigid collisions during docking. Additionally, adaptive robust sliding mode control is developed, enhancing the robot’s tracking accuracy for desired poses and making it suitable for high-precision assembly.

In this paper we present a parallel robot with flexure hinges for target alignment system of a high power laser facility. The robot contains a parallel mechanism with 6 DOF which has nanometer positioning accuracy and is driven by six linear actuators. We design a new flexure hinge which has higher accuracy, strong environmental suitability and simple structure compared with conventional flexure hinge which has backlash and friction issues. The kinematics analysis of the parallel mechanism is also discussed. The simulation analysis of the mechanism is done by ADAMS. The mechanism is proved meeting the design requirements by comparing the results of the theory analysis and the simulations.

Workspace Analysis of the 4RRR Planar Parallel Manipulator with Actuation Redundancy

Parallel mechanisms and manipulators have been part of the robotics landscape for several decades. They have reached a certain level of maturity and commercial products based on these architectures are available for a variety of applications. Nevertheless, it is clear that the full potential of parallel mechanisms has not yet been exploited. Over the last two decades, numerous novel architectures have been proposed and new applications continue to emerge. In this context, research on parallel mechanisms and manipulators continues to flourish, creating a need for international forums in which researchers can exchange ideas and expose new results.

Topology design of (3T-1R) parallel mechanism (PM) based on POC equations is discussed in detail as an example to illustrate the systematic method for topology design of PMs proposed in Chap. 9. The design process includes two stages. The first stage involves traditional structure synthesis, which results in 18 structure types of (3R-1R) PMs that contain no P pairs. The second stage includes topological performance analysis and classification of the obtained PM structure types which may help designer to select the most suitable structure type. Its core contents include: (1) Key steps of topology design for (3R-1R) PMs include: (a) Determine structure types of the SOC branch containing only R and P pairs according to the method for structure synthesis of SOC branch described in Chap.8. Then obtain corresponding HSOC branches through topologically equivalent principle in Chap.9. (b) Determine the geometrical condition for assembling branches between two platforms according to corresponding basic formulas in Chap. 9. Then determine different assembling schemes for the same geometrical condition. (c) Performance analysis and classification of the obtained PM structures are conducted based on topological characteristics of PMs in Chap. 9. The result can be used for assessment and optimization of (3R-1R) PM structure types. (2) 18 types of (3T-1R) PM structures containing no P pair are obtained, two of which have already been used in existing SCARA parallel robots. The other structure types may potentially be used in new SCARA parallel robots. (3) These 18 structure types of (3R-1R) PMs are classified into four types: Type-1 include four PMs containing only SOC branches; Type-2 include six PMs containing only HSOC branches; Type-3 include seven PMs containing both HSOC and SOC branches; Type-4 include three PMs with partial motion decoupling property. (4) According to topological performance analysis and classification of these PMs based on topological characteristics, the type-3 PM has a higher rigidity than a type-1 PM and a larger workspace than a type-2 PM. So, special attentions shall be paid to type-3 PMs.

At present, parallel robots show a great progress in their development due to their behaviour in multiple applications. In this sense, the Stewart-Gough platform with proper mechanical adaptations could be used for a climbing parallel robot. A climbing parallel robot with 6 degrees of freedom has been proposed and analysed. Parallel robots have great advantages compared to serial robots with legs using as climbing robots. Some advantages can be cited as the high weight payload capacity, robustness, simplicity of its mechanical design, etc. However, some difficulties have to be resolve too as the adaptation to the structure meanwhile the robot accomplishes the task or the singularities that can be produced in the movement on the structure. In this paper several options of a climbing parallel robot based in the S-G platform have been presented and analysed. First of all, an initial prototype to climb along tubular structures as pipes or palm trunks has been shown. The main features of this robot are the pneumatic actuators and the external control loop that allows centring the robot to the tubular structure. Taking into account this first prototype, another parallel robot to resolve the problem of displacement and climbing along metallic structures has been presented. The main features of this robot are the electrical actuators and the clamping device developed with the purpose of reducing possible collisions between the movement ring of the robot and the environment. The results achieved with both prototypes show the validity of these platforms to undertake tasks in which are necessary to climb on. In short, this paper tries to show the big potential of using parallel robots as climbing robots. Also, we are working in introducing teleoperation techniques to manage these parallel robots. So, the robots will be controlled in a semi-automatic way when it displaces along the tubular or metallic structures.

This thesis explores the fundamentals of a new class of parallel mechanisms called parallel mechanisms with configurable platforms as well as the design and analysis of parallel robots that are based on those mechanisms. Pure parallel robots are formed by two rigid links, the base and the end-effector, connected in parallel by independent serial chains, called legs. The novel concept behind parallel robots with configurable platforms is that the rigid end-effector is replaced by a closed-loop chain, the configurable platform. Some of the links of this closed-loop chain are attached to the legs so its configuration can be fully controlled from the actuators located on the base. The use of a closed-loop chain instead of a rigid end-effector allows the robot to interact with the environment using multiple contact points on the platform. This results in a robot that can combine motion and grasping capabilities into a structure that provides an inherent high structural stiffness. All the actuators are grounded on the base requiring no additional motor at the end-effector location to provide the grasping. High-speed pick-and-place robots and haptic interfaces are examples of devices that can benefit from this new type of architecture.

A parallel manipulator provides an alternative design to serial manipulators, and can be found in many applications such as mining machines (Arai et al., 1991). Through the design of active joints such that actuators are fixed to the manipulator base, the mass of moving components of the parallel manipulator is greatly reduced, and high speed and high acceleration performance may be achieved. Parallel manipulators, comprised of closed-loop chains due to multiple linkages of the parallel structure, also provide high mechanical rigidity, but adversely exhibit smaller workspace and associated singularities. Considerable research has focused on kinematic analysis and singularity characterization of these devices (Gosselin & Angeles, 1990, Merlet, 1996). Planar parallel manipulators typically consist of three closed chains and a moving platform. According to the arrangement of their joints in a chain, these mechanisms are classified as PRR, RRR etc. where P denotes a prismatic joint and R denotes a revolute joint respectively. An assembly industry, such as the electronic fabrication, demands high-speed, high acceleration placement manipulators, with corresponding lightweight linkages, hence these linkages deform under high inertia forces leading to unwanted vibrations. Moreover, such multiple flexible linkages of a parallel manipulator propagate their oscillatory motions to the moving platform where a working gripper is located. Therefore, such vibration must be damped quickly to reduce settling time of the manipulator platform position and orientation. A number of approaches to develop the dynamic model of parallel manipulators with structural flexibility have been presented in the literature(Fattah et al., 1995, Toyama et al. 2001), but relatively few works related to vibration reduction of a parallel manipulator have been published. Kozak (Kozak et al., 2004) linearized the dynamic equations of a two-degree-of-freedom parallel manipulator locally, and applied an input shaping technique to reduce residual vibrations through modification of the reference command given to the system. Kang (Kang et al., 2002) modeled a planar parallel manipulator using the assumed modes method, and presented a two-time scale controller for linkage vibration attenuation of the planar parallel manipulator. Since both the input shaping technique and the two-time scale control scheme, applied to parallel manipulators,

Developing glucose‐responsive microneedle patches with features of simple preparation, high insulin loading, and safety has a great contribution to the treatment of diabetic patients. In this work, a novel glucose‐responsive core–shell microneedle patch is prepared from biocompatible materials by a facile process. The exterior glucose‐responsive shell is composed of polyvinyl alcohol (PVA) and ɛ‐polylysine modified with phenylboronic acid , and the inner flexible core is prepared by pure PVA loaded with insulin. The shell shows superior glucose‐induced swelling and controlled insulin release ability due to the decomposition of borate ester bonds under the synergistic effect of glucose and water. The microneedle patch also features flexibility and high insulin loading capacity (36 IU cm−2). It shows high puncture efficiency (92%) and maintains a relatively complete morphology after being removed, enabling to reduce material residues in the skin. Moreover, the microneedle patch reveals a good hypoglycemic effect in diabetic rats, achieves a hypoglycemic rate similar to that of direct injection after swelling, and works effectively to prevent excess insulin transmission. The high glucose‐responsive ability, simple preparation, high loading capacity, rapid hypoglycemic speed, high conformability to skin, and low component dissolution make this microneedle patch a suitable candidate for diabetic treatment.

Naturally occurring nanotube with surface modification as biocompatible, target-specific nanocarrier for cancer phototherapy