Ashish Singla

Extension of D-H parameter method to hybrid manipulators used in robot-assisted surgery

The main focus of this work is to extend the applicability of D-H parameter method to develop a kinematic model of a hybrid manipulator. A hybrid manipulator is a combination of open- and closed-loop chains and contains planar and spatial links. It has been found in the literature that D-H parameter method leads to ambiguities, when dealing with closed-loop chains. In this work, it has been observed that the D-H parameter method, when applied to a hybrid manipulator, results in an orientational inconsistency, because of which the method cannot be used to develop the kinematic model. In this article, the concept of dummy frames is proposed to resolve the orientational inconsistency and to develop the kinematic model of a hybrid manipulator. Moreover, the prototype of 7-degree-of-freedom hybrid manipulator, known as a surgeon-side manipulator to assist the surgeon during a medical surgery, is also developed to validate the kinematic model derived in this work.

Lower-limb exoskeletons: Research trends and regulatory guidelines in medical and non-medical applications

With the recent progress in personal care robots, interest in wearable exoskeletons has been increasing due to the demand for assistive technologies generally and specifically to meet the concerns in the increasing ageing society. Despite this global trend, research focus has been on load augmentation for soldiers/workers, assisting trauma patients, paraplegics, spinal cord injured persons and for rehabilitation purposes. Barring the military-focused activities, most of the work to date has focused on medical applications. However, there is a need to shift attention towards the growing needs of elderly people, that is, by realizing assistive exoskeletons that can help them to stay independent and maintain a good quality of life. Therefore, the present article covers the rapidly evolving area of wearable exoskeletons in a holistic manner, for both medical and non-medical applications, so that relevant current developments and future issues can be addressed; this includes how the physical assistance/rehabilitation/compensation can be provided to supplement capabilities in a natural manner. Regulatory guidelines, important for realizing new markets for these emerging technologies, are also explored in this work. For these, emerging international safety requirements are presented for non-medical and medical exoskeleton applications, so that the central requirement of close human–robot interactions can be adequately addressed for the intended tasks to be carried out. An example case study on developing and commercializing wearable exoskeletons to help support living activities of healthy elderly persons is presented to highlight the main issues in non-medical mobility exoskeletons. This also paves the way for the potential future trends to use exoskeletons as physical assistant robots, as covered by the recently published safety standard ISO 13482, to help elderly people perform their activities of daily living.

D-H parameters augmented with dummy frames for serial manipulators containing spatial links

Conventional kinematic studies of serial manipulators involve the proper selection of coordinate frames of reference at appropriate positions. The standard practice, being used in the past, is the use of Denavit-Hartenberg (D-H) algorithm for assigning coordinate frames. However, it has been observed that when an open kinematic chain contains a spatial link with two consecutive joint axes at right angle to each other, the forward kinematics derived with D-H algorithm comes geometrically inconsistent. A typical spatial link involves more than one non-zero link/joint parameters, which are not being accounted for, in the corresponding D-H parameter table. Forward kinematic study of manipulators involving spatial links with two consecutive joint axes at right angles to each other leads to recognizable deficiency of the D-H algorithm, as one of its practical limitation. In the present work, the concept of dummy frames is proposed to eliminate this deficiency. The proposed concept is demonstrated successfully for the case study of a Manipulator for Medical Application (MMA), which is a seven degrees-of-freedom (DOF) manipulator containing spatial links. Both geometrical and physical validation is performed to ensure the efficacy of the proposed concept.

Real-Time Control of a Rotary Inverted Pendulum using Robust LQR-based ANFIS Controller

Abstract From the last five decades, inverted pendulum (IP) has been considered as a benchmark problem in the control literature due to its inherit nature of instability, non-linearity and underactuation. Its applicability in wide range of practical systems, demands the need of a robust controller. It is found in the literature that wide range of controllers had been tested on this problem, out of which the most robust being sliding mode controller while the most optimal being linear quadratic regulator (LQR) controller. The former has a problem of discontinuity and chattering, while the latter lacks the property of robustness. To address the robustness issue in LQR controller, this paper proposes a novel robust LQR-based adaptive neural based fuzzy inference system controller, which is a hybrid of LQR and fuzzy inference system. The proposed controller is designed and implemented on rotary inverted pendulum. Further, to validate the robustness of proposed controller to parametric uncertainties, pendulum mass is varied. Simulation and experimental results show that as compared to LQR controller, the proposed controller is robust to variations in pendulum mass and has shown satisfactory performance.

SimMechanics™ based modeling, simulation and real-time control of Rotary Inverted Pendulum

Rotary Inverted Pendulum is an under actuated, highly nonlinear and unstable system which is widely used for testing various control techniques. The objective of this paper is modeling and simulation of the rotary pendulum QUBE-Servo of Quanser© using second-generation SimMechanics™ toolbox in MATLAB. Results obtained with physical modeling using SimMechanics are validated with the analytical modeling of setup. Physical modeling and simulation are discussed in detail. Further, different control techniques like Pole Placement (PP), Proportional-Derivative (PD) and Linear Quadratic Regulator (LQR) control are implemented for balancing the inverted pendulum in upright position. Thereafter, the results obtained from validated physical model and real-time experimentation are compared and the results are found in close agreement.

Real-Time Swing-up and Stabilization Control of a Cart-Pendulum System with Constrained Cart Movement

Abstract The cart-pendulum system is a typical benchmark problem in the control field. It is a fully underactuated system having one control input for two degrees-of-freedom (DOFs) system. It has highly nonlinear structure, which can be used to validate different nonlinear and linear controllers and has wide range of real-time (realistic) applications like rockets propeller, tank missile launcher, self-balancing robot, stabilization of ships, design of earthquake resistant buildings, etc. In this work, modeling, simulation and real-time control of a cart-pendulum system is performed. The mathematical model of the system is developed using Euler-Lagrange approach. In order to achieve a more realistic model, the actuator dynamics is considered in the mathematical model. The main aim of this work is to investigate the performance of two different control strategies- first to swing-up the pendulum to near unstable equilibrium region and second to stabilize the pendulum at unstable equilibrium point. The swing-up problem is addressed by using energy controller in which cart is accelerated by providing a force to the cart with a AC servo motor with the help of timing pulley arrangement. The initial velocity of the cart is taken into account to confirm swing-up in the restricted track length. The cart displacement in the restricted track length is verified by simulation and experimental test-run. The regulation problem of stabilization of pendulum is addressed by developing the controller using Pole Placement Controller (PPC) and LQR Controller (LQRC). Both the control strategies are performed analytically and experimentally using the Googoltech Linear Inverted Pendulum (GLIP) setup. The analytical results, simulated in MATLAB and SIMULINK environment, are found in close agreement with the experimental results. In order to demonstrate the effect of both the stabilizing controllers on the performance of the system, comparison of the experimental results is reported in this work. It is demonstrated experimentally that LQR controller outperforms the Pole Placement controller, in terms of reduction in the oscillations of the inverted pendulum (56 %), as well as the magnitude of maximum control input (66.7 %). Further, robustness of the closed-loop system is investigated by providing external disturbances.

System Identification of an Inverted Pendulum Using Adaptive Neural Fuzzy Inference System

The objective of this paper is to illustrate the efficiency of adaptive neural fuzzy inference system (ANFIS) in identifying a nonlinear single-input multiple-output (SIMO) system. The SIMO system used for demonstration is cart-inverted pendulum, which is well known for its highly nonlinear, unstable, and under-actuated nature. The ANFIS model of cart-inverted pendulum (CIP) is designed in Matlab Simulink environment using input–output data obtained from nonlinear mathematical model. The simulation responses for different initial conditions are obtained from ANFIS model which are further compared to the mathematical model of the system. It was observed that within the trained operating range, ANFIS model exactly replicated the nonlinear mathematical model of the system while a little deviation is observed outside the trained operating range. Thus, the authors propose to use ANFIS for system identification from experimental input–output data when the system parameters are unknown or uncertain.

Toward Human-Powered Lower Limb Exoskeletons: A Review

Most of the commercially available exoskeletons use rechargeable Li-ion batteries, which require frequent charging. The battery charging becomes a big bottleneck, when the person, wearing the exoskeleton, needs to go for a week trip on trekking or mountaineering. In order to make batteries more reliable and portable, an alternative energy source can be a good option. Human-powered devices are useful as an emergency electric power source, during natural disaster, war, or civil disturbance make regular power supplies unavailable. These devices have also been treated as an economical and environment-friendly option for use in underdeveloped countries, where batteries may be expensive and main power supply is unreliable or sometimes unavailable. Some of the environmental-energy-producing sources are piezoelectric devices, vibrational sources, RF transmitters, etc., where each method produces different amount of electricity. Some of these sources do not produce enough energy to charge an exoskeleton’s battery. Therefore, in this article, an effort has been made to review the human-powered products in order to develop a mechanism that can be used for charging the battery of exoskeletons. Human power is defined as the use of human work for energy generation. The energy is harvested from the user’s daily actions (walking, breathing, body heat, blood pressure, finger motion, etc.). This paper compares the various conventional and alternative methods to charge lower limb exoskeletons to be used for elderly people.

Kinematic modeling of a 7-degree of freedom spatial hybrid manipulator for medical surgery:

The prime objective of this work is to deal with the kinematics of spatial hybrid manipulators. In this direction, in 1955, Denavit and Hartenberg proposed a consistent and concise method, known as D-H parameters method, to deal with kinematics of open serial chains. From literature review, it is found that D-H parameter method is widely used to model manipulators consisting of lower pairs. However, the method leads to ambiguities when applied to closed-loop, tree-like and hybrid manipulators. Furthermore, in the dearth of any direct method to model closed-loop, tree-like and hybrid manipulators, revisions of this method have been proposed from time-to-time by different researchers. One such kind of revision using the concept of dummy frames has successfully been proposed and implemented by the authors on spatial hybrid manipulators. In that work, authors have addressed the orientational inconsistency of the D-H parameter method, restricted to body-attached frames only. In the current work, the condition of body-attached frames is relaxed and spatial frame attachment is considered to derive the kinematic model of a 7-degree of freedom spatial hybrid robotic arm, along with the development of closed-loop constraints. The validation of the new kinematic model has been performed with the help of a prototype of this 7-degree of freedom arm, which is being developed at Council of Scientific & Industrial Research–Central Scientific Instruments Organisation Chandigarh to aid the surgeon during a medical surgical task. Furthermore, the developed kinematic model is used to develop the first column of the Jacobian matrix, which helps in providing the estimate of the tip velocity of the 7-degree of freedom manipulator when the first joint velocity is known.

Adaptive neuro-fuzzy inference system–based path planning of 5-degrees-of-freedom spatial manipulator for medical applications:

Over the last few decades, medical-assisted robots have been considered by many researchers, within the research domain of robotics. In this article, a 5-degrees-of-freedom spatial medical manipulator is analyzed for path planning, based on inverse kinematic solutions. Analytical methods have generally employed for finding the inverse kinematic solutions in earlier studies. However, this method is only appreciable in case of closed-form solutions. The unusual joint configurations of considered manipulator result in more complexity to attain the closed-form solutions, analytically. To overcome with shortcomings of analytical method, a non-traditional approach named adaptive neuro-fuzzy inference system is proposed under the class of artificial intelligent techniques. This article presents this neuro-fuzzy approach for desired path generation by 5-degrees-of-freedom manipulator. The estimation of percentage error between actual path and adaptive neuro-fuzzy inference system–generated path is done with respect to x, y, and z directions, respectively. Furthermore, the error between actual and predicted values regarding joint parameters is calculated for a certain arm matrix. The prototype of 5-degrees-of-freedom medical-assisted manipulator is developed at CSIR-CSIO Laboratory Chandigarh, which is also termed as patient-side manipulator to be utilized in robot-assisted surgery. Through the simulation runs, in this work, it is found that the results from adaptive neuro-fuzzy inference system approach are quite satisfactory and acceptable.