Feedforward and Modal Control for a Multi Degree of Freedom High Precision Machine

High precision industrial machines suffer the presence of vibrations due to several noise sources: ground vibration, acoustic noise, direct force disturbances. In the last years the need of higher processing quality and throughput result in a continuing demand for higher accuracy. Therefore vibration isolation systems became mandatory to satisfy these requests. In general, machine supports are designed for high stiffness to obtain a robust machine alignment with respect to its surroundings. However, in the presence of significant ground vibration levels the support stiffness is commonly sacrificed to reduce their transmission to the payload stage. Efforts to go towards these issues are recorded in several applications and the solutions are different for any particular situation, depending on the nature of the vibration sources, the amount of the disturbances and the machine environment. This chapter focuses on the evaluation of a vibration isolation device on the working cell of a micro-mechanical laser center, using active electromagnetic actuators. The machine is composed by two main parts: a frame support and a payload stage where the laser cutting is performed. The machine potential in terms of accuracy and precision is reduced by the presence of two main vibration sources: the ground and the stage itself. The active device should meet two main goals: the payload vibrations damping and the reduction of the transmissibility of ground disturbances. In this work the phases followed to design, realize and validate the device are illustrated with a particular attention to the mechatronics aspects of the project and to the control strategies. The chapter starts on the description of the common solutions and of the techniques described in literature. The requirements analysis and a trade-off phase on the available opportunities for vibration isolation are described. An analysis of the plant components is reported in the second section along with an exhaustive explanation of a) actuation subsystem consisting in four voice-coils, two per axis; b) sensing subsystem aimed to measure the absolute velocities of the frame support and of the stage are measured by means of eight geophone sensors. The considerations leading to the choice of this sensing system are reported along with the signal conditioning block. The active control is performed with a digital platform based on DSP and FPGA. The core of the chapter is the description of the modeling approach and of the control strategies design. The bond-graph approach is used to represent the system behavior, in particular the interactions between the mechanical and electrical subsystems are illustrated. The realized model includes the plant, the sensing, the control and the actuation blocks. The plant is considered as a classical two mass-spring-damper system resulting on a multi-input multi-output system (MIMO), considering disturbances from the stage and the ground and the actuators action between the two masses. Time and frequency domain computations are carried out from the model to evaluate vibration levels and displacements and to identify which parameters need to be carefully designed to satisfy the requirements. The control strategy is focused on the attenuation of the effects of microvibrations on the stage caused by different sources. The technique consists in a combination of two actions, the goal being the minimization of the ground vibrations transmission and the payload vibrations damping: • A single-axis decentralized action consisting in a modal controller used to compensate the high-pass band dynamic of the geophone sensors and to control the vibrations. • A feedforward action working on the disturbances coming from the payload and from the ground. This control is not generated in on-line, but computed in advance from the data of machine responses to the direct disturbances coming from the floor and the stage and resulting in vibrations on the payload and on the frame. The first action itself is aimed to perform active isolation and vibration that nevertheless could be not sufficient for severe specifications applications. The feedforward action is hence used to face this shortcoming by suppressing direct disturbance. The controller design phases along with its performance evaluation are described. The chapter concludes on the illustration of the results obtained with the proposed modeling and control strategy

Flight control systems properties and problems, volume 1

This volume contains a delineation of fundamental and mechanization-specific flight control characteristics and problems gleaned from many sources and spanning a period of over two decades. It is organized to present and discuss first some fundamental, generic problems of closed-loop flight control systems involving numerator characteristics (quadratic dipoles, non-minimum phase roots, and intentionally introduced zeros). Next the principal elements of the largely mechanical primary flight control system are reviewed with particular emphasis on the influence of nonlinearities. The characteristics and problems of augmentation (damping, stability, and feel) system mechanizations are then dealt with. The particular idiosyncracies of automatic control actuation and command augmentation schemes are stressed, because they constitute the major interfaces with the primary flight control system and an often highly variable vehicle response

A lightweight, high strength dexterous manipulator for commercial applications

The concept, design, and features are described of a lightweight, high strength, modular robot manipulator being developed for space and commercial applications. The manipulator has seven fully active degrees of freedom and is fully operational in 1 G. Each of the seven joints incorporates a unique drivetrain design which provides zero backlash operation, is insensitive to wear, and is single fault tolerant to motor or servo amplifier failure. Feedback sensors provide position, velocity, torque, and motor winding temperature information at each joint. This sensing system is also designed to be single fault tolerant. The manipulator consists of five modules (not including gripper). These modules join via simple quick-disconnect couplings and self-mating connectors which allow rapid assembly and/or disassembly for reconfiguration, transport, or servicing. The manipulator is a completely enclosed assembly, with no exposed components or wires. Although the initial prototype will not be space qualified, the design is well suited to meeting space requirements. The control system provides dexterous motion by controlling the endpoint location and arm pose simultaneously. Potential applications are discussed

Design and Implementation of Position Estimator Algorithm on Voice Coil Motor

Voice Coil Motors (VCMs) have been an inevitable element in the mechanisms that have been used for precise positioning in the applications like 3D printing., micro-stereolithography., etc. These voice coil motors translate in a linear direction and require a high accuracy position sensor that amounts for a major part in the budget. In this research work., an effort has been made to design and implement an algorithm that would predict the displacement of VCM and eliminate the need of high cost sensors. VCM was integrated with dSPACE DS1104 R&D controller via linear current amplifier (LCAM) which acts as a driver circuit for VCM. Sine input was given to VCM with various amplitude and frequency and the corresponding displacement is measured by using linear variable differential transformer (LVDT). The position estimator algorithm is also implemented at the same time on VCM and its output is compared with that of LVDT. It is observed that there is 97.8 % accuracy in between algorithm output and LVDT output. Further., PID controller is used in integration with the novel algorithm to minimize the error. The estimator algorithm is tested for various amplitudes and frequencies and it is found that it has a very good agreement of 99.2% with the actual displacement measured with the help of LVDT

Redundant actuator development program

Two concepts of redundant secondary actuator mechanization, applicable to future advanced flight control systems, were studied to quantitatively assess their design applicability to an AST. The two actuator concepts, a four-channel, force summed system and a three-channel, active/standby system have been developed and evaluated through analysis, analog computer simulation, and piloted motion simulation. The quantitative comparison of the two concepts indicates that the force summed concept better meet performance requirements, although the active/standby is superior in other respects. Both concepts are viable candidates for advanced control application dependent on the specific performance requirements

Actuators for a space manipulator

The robotic manipulator can be decomposed into distinct subsytems. One particular area of interest of mechanical subsystems is electromechanical actuators (or drives). A drive is defined as a motor with an appropriate transmission. An overview is given of existing, as well as state-of-the-art drive systems. The scope is limited to space applications. A design philosophy and adequate requirements are the initial steps in designing a space-qualified actuator. The focus is on the d-c motor in conjunction with several types of transmissions (harmonic, tendon, traction, and gear systems). The various transmissions will be evaluated and key performance parameters will be addressed in detail. Included in the assessment is a shuttle RMS joint and a MSFC drive of the Prototype Manipulator Arm. Compound joints are also investigated. Space imposes a set of requirements for designing a high-performance drive assembly. Its inaccessibility and cryogenic conditions warrant special considerations. Some guidelines concerning these conditions are present. The goal is to gain a better understanding in designing a space actuator

ChainQueen: A Real-Time Differentiable Physical Simulator for Soft Robotics

Physical simulators have been widely used in robot planning and control. Among them, differentiable simulators are particularly favored, as they can be incorporated into gradient-based optimization algorithms that are efficient in solving inverse problems such as optimal control and motion planning. Simulating deformable objects is, however, more challenging compared to rigid body dynamics. The underlying physical laws of deformable objects are more complex, and the resulting systems have orders of magnitude more degrees of freedom and therefore they are significantly more computationally expensive to simulate. Computing gradients with respect to physical design or controller parameters is typically even more computationally challenging. In this paper, we propose a real-time, differentiable hybrid Lagrangian-Eulerian physical simulator for deformable objects, ChainQueen, based on the Moving Least Squares Material Point Method (MLS-MPM). MLS-MPM can simulate deformable objects including contact and can be seamlessly incorporated into inference, control and co-design systems. We demonstrate that our simulator achieves high precision in both forward simulation and backward gradient computation. We have successfully employed it in a diverse set of control tasks for soft robots, including problems with nearly 3,000 decision variables.Comment: In submission to ICRA 2019. Supplemental Video: https://www.youtube.com/watch?v=4IWD4iGIsB4 Project Page: https://github.com/yuanming-hu/ChainQuee

Apollo docking test device design study final report

Docking simulation system for confirming Apollo probe design and drogue docking mechanisms under simulated space condition

Stiffness Imaging With a Continuum Appendage: Real-Time Shape and Tip Force Estimation From Base Load Readings

In this paper, we propose benefiting from load readings at the base of a continuum appendage for real-time forward integration of Cosserat rod model with application in configuration and tip load estimation. The application of this method is successfully tested for stiffness imaging of a soft tissue, using a 3-DOF hydraulically actuated braided continuum appendage. Multiple probing runs with different actuation pressures are used for mapping the tissue surface shape and directional linear stiffness, as well as detecting non-homogeneous regions, e.g. a hard nodule embedded in a soft silicon tissue phantom. Readings from a 6-axis force sensor at the tip is used for comparison and verification. As a result, the tip force is estimated with 0.016-0.037 N (7-20%) mean error in the probing and 0.02-0.1 N (6-12%) in the indentation direction, 0.17 mm (14%) mean error is achieved in estimating the surface profile, and 3.4-15 [N/m] (10-16%) mean error is observed in evaluating tissue directional stiffness, depending on the appendage actuation. We observed that if the appendage bends against the slider motion (toward the probing direction), it provides better horizontal stiffness estimation and better estimation in the perpendicular direction is achieved when it bends toward the slider motion (against the probing direction). In comparison with a rigid probe, ≈ 10 times smaller stiffness and ≈ 7 times larger mean standard deviation values were observed, suggesting the importance of a probe stiffness in estimation the tissue stiffness