This paper proposes a bilateral control structure with a realization of the force derivative in the control loop. Due to the inherent noisy nature of the force signal, most teleoperation schemes can ...make use of only a proportional (P) control structure in the force channel of the bilateral controllers. In the proposed scheme, an α–β–γ filter is designed to smoothly differentiate the force signal obtained from a reaction force observer integrated to both of the master and slave plants. The differentiated force signal is then used in a proportional-derivative (PD) force controller working together with a disturbance observer. In order to design the overall bilateral controller, an environment model based on pure spring structure is assumed. The controller is designed to enforce an exponentially decaying tracking error for both position and force signals. With the presented controller design approach, one can independently tune the controller gains of the force and the position control channels. The proposed approach is experimentally tested in a platform consisted of direct drive linear motors. As illustrated by the experiment results, the contribution of the PD control in the force channel improves the teleoperation performance especially under hard-contact motion scenarios by attenuating the oscillations, hence, improving the transparency when compared to the structures using only a P force control.
The main research topic of this paper is to apply the sliding mode based soft actuation to smooth transition between position, force, and impedance control, and realize bilateral control and ...reproduction of the haptic motion. The proposed design rests on the sliding mode two steps procedure: in the first step, the generalized error — the sliding mode function — is selected in such a way that a closed loop system exhibits a desired dynamics. In the soft actuation method, the generalized error depends on the position and the force, thus allowing the modification of the position tracking if interaction with the environment appears. In the second step, the control is selected to enforce the desired convergence rate and the stability of the closed loop dynamics. The control allows “natural — human-like” behavior. The application to the bilateral control and reproduction of the haptic motion is discussed in detail and verified by experiments.
This work demonstrates the design, implementation, and experimental results of a low-cost disposable flexible sensor system capable of both impact localization and measurement. The proposed flexible ...sensor structure utilizes a special series of Bristol paper as the main fabrication material, which is coated with electric paint graphite paste and silver paste. The implemented sensor system uses a planar absolute encoder-like sensing topology to locate the impact and has a low-cost and quick manufacturing process. The size of the structure is <inline-formula> <tex-math notation="LaTeX">{210}\times {18}.{56} </tex-math></inline-formula> mm with a thickness of approximately 340 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>. It has an electronic read-out consisting of three identical Wheatstone bridge circuits and instrumentation amplifiers for each bit. It can detect the external forces in the range of 0.6N to 12N with a spatial resolution of 2.4 cm and 0.55 cm in horizontal and vertical axes, respectively. The proposed sensor structure is tested in a series of experiments using a robotic setup consisted of a pantograph mechanism and a direct drive linear motor. The experiments illustrate the results with measurement sensitivity as small as 1N and proper fatigue resilience against repetitive loads.
This paper presents a unified formulation for the kinematics, singularity and workspace analyses of parallel delta robots with prismatic actuation. Unlike the existing studies, the derivations ...presented in this paper are made by assuming variable angles and variable link lengths. Thus, the presented scheme can be used for all of the possible linear delta robot configurations including the ones with asymmetric kinematic chains. Referring to a geometry-based derivation, the paper first formulates the position and the velocity kinematics of linear delta robots with non-iterative exact solutions. Then, all of the singular configurations are identified assuming a parametric content for the Jacobian matrix derived in the velocity kinematics section. Furthermore, a benchmark study is carried out to determine the linear delta robot configuration with the maximum cubic workspace among symmetric and semi-symmetric kinematic chains. In order to show the validity of the proposed approach, two sets of experiments are made, respectively, on the horizontal and the Keops type of linear delta robots. The experiment results for the confirmation of the presented kinematic analysis and the simulation results for the determination of the maximum cubic workspace illustrate the efficacy and the flexible applicability of the proposed framework.
Sub-millimeter scale devices are developing rapidly taking smaller, smarter, and more precise forms. This is achieved thanks to advancements in micro-manufacturing tools and techniques. For ...micro-production, a miniaturization of the machinery is a prominent idea that has numerous benefits in terms of material usage, precision, transportation, modularity, and reconfigurability. In this paper, a modular and reconfigurable desktop microfactory for high precision machining and assembly of sub-millimeter scale mechanical parts is presented and experimentally validated. The proposed system is built based on important functional and performance requirements, including miniaturization, high precision operation, modular and reconfigurable design, parallel processing capability, ease of installation, and transportation. The miniature factory consists of five mini processing units; two parallel kinematic robots for manipulation, the laser micro-machining system, the camera system for detection and inspection, and the rotational conveyor system for micro-part delivery. Different configurations of the system layout are proposed taking advantage of their modular design. Experiments are conducted to evaluate the system performance within a single process, like pick-place of a metallic ball with 3 mm diameter, laser machining of a half-millimeter size contour on the surface of the ball, and inspection and verification of the machined contour by means of microscopic camera. The results presented in this work demonstrate micrometer precision operation of the microfactory, showing high potential for manufacturing electro-mechanical devices with ease of readjustment of the microfactory layout.
Mecanum wheeled robots can exhibit serious slippage problems because of the discontinuous contact between the wheels and the ground which negatively influences the overall navigation quality. ...Addressing this problem, the aim of this paper is to demonstrate how a learning-based method can be used for the estimation of the drifting error from multiple sensors with distinct measurement types. Here, a recurrent neural network (RNN)-based drift compensation algorithm is proposed for the estimation of the positioning drift. In order to improve the positioning performance in dead reckoning the estimated drift is used within the real-time control loop for proper modification of the motion trajectory. During the training phase, the data acquired from the acceleration sensors attached to the robot chassis and the encoders of the wheels of the robot are used as the main features to train a gated recurrent unit-based RNN. The drift estimator is trained using the computer-generated reference position data, and the response position data which is measured using an optoelectronic motion tracking device. The performance of the proposed learning-based drift estimation and control algorithm is validated through a series of experiments. The responses obtained from the experiments are graphically illustrated and the improvements in the positioning performances are numerically evaluated. The results obtained from the experiments illustrate the effective performance of the proposed algorithm by considerably decreasing the positioning errors.
This paper investigates the bilateral teleoperation with the possibility of continuously variable scaling during real-time operation. The algorithm proposed for this purpose provides the operator ...with the ability to change the scaling gains of force and velocity loops during operation. The controllers are derived to enforce exponentially decaying error dynamics on systems which have inner loop disturbance compensation. The proposed architecture assumes the scale factors as continuous functions of time which have continuous derivatives that are also included in the mathematical derivation. Unlike the existing studies, the presented framework allows real-time adaptation of scaling gains, which provides the user with the ability to conduct coarse and fine motion in the same operation. The Lyapunov stability proof of the proposed method is made and the margins of the controller gains are identified for practical operation. Furthermore, the operational accuracy is enhanced by the application of a PD force control loop which is also new for scaled bilateral teleoperation. The realization of PD loop is made using an
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filter to differentiate the force signal. The algorithm is validated on a setup consisted of two single DOF motion control systems. In order to provide a complete analysis, a wide range of experiments are made, velocity and force scales having sinusoidal patterns with different amplitudes and frequencies. Moreover, comparison with a classical bilateral control architecture is made to highlight the flexibility of the proposed control method. The efficacy of the proposed approach is solidified by the successful tracking responses obtained from these experiments.
Owing to the increasing engagement of service robots in everyday life, significant requirements are imposed on their control systems to ensure safe interaction between robots and humans. The ...stiffness of the motion executed by the service robots is not high, as with industrial robots, but has to be variable depending on the defined task. Therefore, a service robot needs to have soft actuation, delivering "human-like" motion dependant on the interaction force between the robot and its environment. Such an operation requires switching from the trajectory tracking (position control) mode to the interaction (force control) mode, and vice versa . Conventional control methods, based on hybrid position/force control, or switching between a position and force controller, may fail short in these cases. Thus, we have previously proposed a new control method, denoted as universal motion controller, that merges the position and force control into a single control structure. The control method is elaborated in this article, and its experimental validation is presented for the first time for multi-degree-of-freedom systems.
In this study, a novel compression and decompression algorithm, namely the selected discrete cosine transform (DCT), is presented for implementation in networked motion control systems. The proposed ...method relies on the utilization of a selection algorithm based on bubble sorting to choose the highest power coefficients of the signal obtained by using DCT. In order to better illustrate the effectiveness of the proposed method, comparisons are made with the methods existing in the literature. To this aim, the basics of the compression schemes used in the comparison, namely, the DCT, discrete Fourier transform, and wavelet packet transform, are also briefly discussed followed by the derivation of the proposed method. The algorithmic bases of all four schemes are given to provide further reference for practical applications. The proposed method is tested on an experimental platform consisting of a single-single-degree-of-freedom master and slave systems, and the results are comparatively analyzed based on relevant performance evaluation metrics. The obtained results demonstrate the improvement achieved by the proposed compression scheme over the existing compression methods used in network-based motion control applications, hence proving the feasibility of the approach in teleoperation systems.
U članku se raspravlja o algoritmu za generiranje trajektorija, metodi za konstrukciju pogreške konture te o sintezi konturnog regulatora. U algoritum za generiranje trajektorija, korištena je ...kombinacija eliptičnih Fourierovih odrednika (EFD) i vremenske aproksimacije splajnovima (TBSA) za odre.ivanje referentnih vrijednosti položaja, brzine i ubrzanja. Pogreška konture je konstruirana korištenjem transformirane pogreške slije.enja trajektorije. Transformacija je računski efikasna i potrebna joj je samo informacija o referentnoj brzini. Konturni regulator je projektiran koristeći upravljanje u kliznim režimima. Provedeni su eksperimenti na linearnom slijednom sustavu i primijećena su znatna smanjenja pogreške konture.
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