Construction of hardware-in-the-loop simulation system for numerical control force control based on an industrial automation programme

This paper describes robust force sensorless control system in motion control. Motion control technology has been contributed to a variety of industrial applications. The achievement of force control is one of the deep technical issues in motion control and industrial applications. Force control has been researched for more than four decades. Generally, force sensor has been utilized in force control. However, a force sensor has certain disadvantages and prevents the realization of precise force control. Especially, sensor noise causes degradation on control performance. Thus, force sensorless control has been developed. Here, both performances of a force control system with force sensor and force sensorless control system are observed in experiments. In addition, external forces are classified into reaction forces and action forces. Most force control systems are targets of reaction force control. However, action force control system is required to adopt to more variety applications. Thus, at first, reaction force control system and action force control system are described. In addition, the relationship between both force control system and control stiffness is expressed. Control stiffness is a performance index of motion control. Control stiffness is then used to evaluate the performance of both force control system. Experimental results are presented the behavior of reaction force control and action control

Traditional industrial robots have problems interacting with an uncalibrated, ill-defined environment where part geometry and position may vary. Active force control technology has therefore been suggested as a solution to add the extra sensory dimension needed to handle manufacturing tasks like assembly and deburring. The technology is proposed to give increased flexibility compared to other solutions and force control systems are available commercially. Active force control installations, however, are still uncommon in industry. This paper presents two cases of force control applications; assembly of a compliant carbon fiber structure and deburring/cleaning of iron castings. Based on these two cases, some issues are raised concerning how the technology can be further developed to fit the industrial setting, and the proposed benefits are re-examined and refined. The two cases show that programming, parameter setting and ease of use are critical components in lowering the industrial threshold, together with increased possibilities for application-specific compensation and filtering. Force control does, however, show great potential in extending the boundaries for variance in product and equipment like grippers and fixtures as well as decreasing the need for calibration of for example virtual models used for programming compared to traditional automated solutions.

Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit (HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness.

An intelligent arm-wrestling system recently developed in our laboratory is comprised of an arm-force generation mechanism and a control system that detects the maximum arm-force of a user in the early stage of the match, generates a different game scenario each time, and executes force feedback control to implement the scenario. This paper presents a mathematical modeling of the force control system of the intelligent arm-wrestling system via experimental frequency responses using a control system analyzer, and force control of the system. The validity of the derived model and force control logic is demonstrated through simulation and experimental studies

Controlling robots in contact with environment is the important problem in industry applications. In the conventional force control, great many researches have paid attention to develop novel force control systems and implemented force sensors to detect external force. Narrow bandwidth of force sensor has a big influence on the force control system. In order to solve the instability in force control, the velocity feedback gain is enlarged. The system becomes unstable with small velocity feedback gain, and robot's response becomes slow with large one. Since there is trade-off between stability and responsivity, it is thought that force control by robots is difficult. As a result, it is trapped in a vicious circle of narrowing further the frequency band which a force sensor has. Force control is attainable by the construction of the easiest force control architecture by feedback of observer. It is possible to set any bandwidth due to the sampling time and observer gain. This paper shows that bandwidth of force sensing is very important for contact motion control. Sensor-less force control is the one of the fundamental techniques for evolution of human-cooperating robot. The numerical and experimental results show viability of the proposed method.

This paper studies an integrated design method of sensorless force control and current control systems. The force control gain, the estimation bandwidth and quality factor of a 1st-order disturbance observer, the proportional and integral gain of an I-P current controllers are determined analytically and numerically by Pole assignment method and Coefficient diagram method(CDM). In the case of Pole assignment and CDM, the force responses converge with the force command without any oscillations and overshoot. By the simulations and experiment, the validity of the integrated design method proposed in this paper is verified. Furthermore, this paper presents that not only the parameters of the force control system but also the gain of the I-P current controllers have to be varied depending on the environmental stiffness.

Each joint of a hydraulic-driven legged robot adopts a highly integrated hydraulic drive unit (HDU), which features a high power–weight ratio. However, most HDUs are throttling-valve-controlled cylinder systems, which exhibit high energy losses. By contrast, pump control systems offer a high efficiency. Nevertheless, their response ability is unsatisfactory. To fully utilize the advantages of pump and valve control systems, in this study, a new type of pump–valve compound drive system (PCDS) is designed, which can not only effectively reduce the energy loss, but can also ensure the response speed and response accuracy of the HDUs in robot joints to satisfy the performance requirements of robots. Herein, considering the force control requirements of energy conservation, high precision, and fast response of the robot joint HDU, a nonlinear mathematical model of the PCDS force control system is first introduced. In addition, pressure–flow nonlinearity, friction nonlinearity, load complexity and variability, and other factors affecting the system are considered, and a novel force control method based on quantitative feedback theory (QFT) and a disturbance torque observer (DTO) is designed, which is denoted as QFT–DTOC herein. This method improves the control accuracy and robustness of the force control system, reduces the effect of the disturbance torque on the control performance of the servo motor, and improves the overall force control performance of the system. Finally, experimental verification is performed using the PCDS performance test platform. The experimental results and quantitative data show that the QFT–DTOC proposed herein can significantly improve the force control performance of the PCDS. The relevant force control method can be used as a bottom-control method for the hydraulic servo system to provide a foundation for implementing the top-level trajectory planning of the robot.

Controlling robots in contact with the environment is an important problem in industry applications. In the conventional force control, much research has paid attention to develop novel force control systems and implemented force sensors to detect external force. This paper shows that narrow bandwidth of force sensor has a big influence on the force control system. Generally, to solve the instability in force control, the velocity feedback gain is enlarged. The system becomes unstable with small velocity feedback gain, and robot's response becomes slow with large one. Inasmuch as there is a tradeoff between the stability and the response, it is considered that force control by robots is difficult. This paper proposes a force control system with disturbance observer. It is possible to obtain the force information with wide bandwidth by using the disturbance observer. This paper shows that bandwidth of force sensing is very important for contact motion control. By using the wide bandwidth of force sensing, both stability and response are improved. Furthermore, force control is attainable by the construction of the easiest force control architecture. Therefore, the ideal zero-stiffness-force control is attained. The numerical and experimental results show viability of the proposed method.

This paper proposes a force control system including contact process using acceleration-sensor-based instantaneous state observer for high-stiffness gear drive. The proposed system is structured by PI velocity control system and IP force control system based on resonance ratio control system. An instantaneous state observer is used to a resonance ratio control system for a high-stiffness gear drive. In proposed system, the robot arm of a high-stiffness gear drive is achieved to move closer to the environment by using PI velocity control system. Moreover, the robot arm is achieved to come in contact with the environment by using IP force control system. Additionally, the force control system including contact process is needed a smooth switching of these control system, and smooth force control. To achieve the smooth switching of control system, an initial value of an integrator of force control system is calculated by the condition that a motor-side torque reference is constant when switching the control system. In addition, the algorithm is proposed to achieve the smooth force control system. The proposed method is achieved the smooth switching of control system and smooth force control system. The effectiveness of proposed method is confirmed by numerical simulation and experiments.

This article proposes that this known significant discrepancy between the Weighted Sum Ground Force (WSGF) prediction of the vibrator output (the Sallas Approximation; see Sallas, 1984) and downhole measurements of the output is not so much a ‘lie’, as it is simply the natural consequence of the limitations and inaccuracies of the WSGF model. The authors believe that these model deficiencies arise from a woefully incomplete understanding of the complex interaction of the vibrator mechanism with the ground. If this is correct, than an improved understanding of the interactions of the vibrator mechanism and the ground during a sweep should lead to a more complete model of the vibrator/earth interactions, with significant improvements in both the actual energy content of the propagating wavelet as well as more ‘truthful’ quality control reporting thereof. Modern vibrator control systems use both phase and force control systems in controlling the output motions of the reaction mass (RM) and baseplate (BP). Feedback from various sensors on the vibrator mechanism is used to adjust the input hydraulic controls so that the WSGF ‘mimics’ the desired reference sweep. In this paper we examine the response of a downhole vertical geophone to a broadband sweep generated on the surface, initially with both force and phase control operating, and then with force control disabled, to observe what effects force control has on the vibrator mechanism and the propagating seismic wavelet, as well as to develop an improved understanding of the interaction of the vibrator mechanism with the ground during a sweep.

This paper investigates the design and implementation of a force and position servo control system where non-linearities are encountered due to constraint on the torque signal to the motor drive, and switching between position and force controllers. The so-called two-step design paradigm is employed, whereby the velocity, position and force controllers are designed first ignoring control input non-linearities, and then anti-windup and conditioned transfer compensators are added using the Hanus conditioning technique. Both linear position and force controllers are designed using the H∞ loop shaping design procedure, and the H∞ controllers are found such that the Hanus conditioning technique for anti-windup conditioned transfer compensation can be applied. The overall controller is derived and presented in the state space framework, and its performance is evaluated in real time on an experimental set-up using a commercial digital signal processor.

This paper deals with a control scheme for autonomous underwater robots equipped with manipulators. Several motion and force controllers have been developed. Most of them were designed in disregard of the dynamics of marine thrusters to develop a controller with a simple structure. However, the robot body propelled by thrusters generally has a considerably slower time response than the manipulator driven by electrical motors. Therefore, it may be difficult to construct a high-gain feedback control system to achieve a good control performance, because the high gain may excite the slow thruster dynamics ignored in the controller design, and the excitation will degrade the control performance. In this paper, we develop a motion and force controller for mathematical models with the dynamics of thrusters. It includes a nonlinear force error filter which allows us to construct a stable motion and force control system. To investigate its control performance, we conducted numerical simulations for comparing the proposed control scheme with an existing control scheme designed in disregard of the thruster dynamics. Simulation results demonstrate the usefulness of the proposed controller.

Disturbances are one of the major challenges that should be dealt with when designing high performance force control systems for robots that interact with unknown environments. To achieve high performance dynamic interaction, this paper presents a robust force control system that implements a force disturbance observer (FDOB). Dynamic compliance with the environment is greatly improved with this control technique. The whole force control structure consists of a servo system with a force sensor, the proposed FDOB, feedforward and feedback controllers, and the low-pass filter for attenuating measurement noises of the force sensor feedback signal. The nominal model of the proposed FDOB is obtained by nonparametric system identification method. The FDOB then estimates disturbances by utilizing the motor torque and force sensor measurement signals as its inputs. Theoretical analyses of the FDOB and the overall force control system are conducted. To validate the proposed control structure, experiments are conducted while considering various scenarios from where it is found out that it shows superior performance over the conventional force control method.

In recent years, the industrial researchers have paid attention to the not only position control but also force control. The one target of force control researches is the injection molding machine. The conventional force control system uses the force sensor to detect the inserted force. However, the force control system using force sensor has some problems such as the noise, the frequency band and so on. This paper newly proposes that the reaction torque observer is applied to the injection molding machine using ball screw. The reaction torque observer solves this problem of force sensor. However, it is well-known that the ball screw system has the resonant frequency caused by the torsion phenomenon. Hence, this torsion vibration affects both performances of force control and reaction torque estimation. This paper proposes a new reaction torque observer considering the torsion phenomenon and the friction torque. The proposed reaction torque observer estimates the reaction torque accurately. Moreover, as the outside of proposed reaction torque observer has its friction model, this friction model can be tuned without considering the stability condition of force control feedback system. The validity of proposed force control system is confirmed by the experimental results. This paper realizes the low cost and space-saving injection molding machine by using the proposed force sensor-less control method.

Force Interaction and Control of Two-Arm Manipulators