Multi-Component Force Sensing Systems

Qiaokang Liang

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000358636
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Applied Sciences
• Index: Technology & Engineering

Multi-Component Force Sensing Systems focuses on the design, development, decoupling, and applications of multi-component force sensing systems. Force and moment information can be used as feedback to form an automatic control system to accomplish efficient manipulation. The origins of force measurement and control can be traced back to the late 1970s. Since then, multi-component F/M (force/moment) sensing systems have been widely known and intensively studied. In the past few years, force measurement practices have been significantly affected by new tools (such as digital force gauges, virtual instrumentation, high speed data acquisition systems, etc.) as well as sophisticated measurement methods such as mechano-magnetic, mechano-optical, etc. However, this is the first book to provide an overview of the topic. It will be a useful reference for students in physics and engineering working with robotic sensing systems and robotic systems, in addition to researchers and those working within industry. This work was supported in part by the National Nature Science Foundation of China (NSFC 62073129 and 61673163).

Features:

• Explores the development of force/torque sensing systems

• Provides real applications of the multi-component force/torque sensing systems

• Contains executable code for decoupling algorithms

About the Author:

Qiaokang Liang is an Associate Professor with the College of Electrical and Information Engineering, Hunan University. He is currently the vice director of the Hunan Key Laboratory of Intelligent Robot Technology in Electronic Manufacturing and serving as the assistant director of the National Engineering Laboratory for Robot Vision Perception and Control. He received his Ph.D. degree in control science and engineering from the University of Science and Technology of China, Hefei, China, in 2011. His research interests include robotics and mechatronics, biomimetic sensing, advanced robot technology, and human–computer interaction.

CHAPTER 1

Introduction

Autonomous and intelligent control is one of the main trends in research and development of robotics. The perception and feedback are necessary means for robot intelligent behaviors, and the level of intelligent control depends largely on the comprehensive understanding of the environment in which the perception and interaction system is located. High-quality visual and force perception information is the most important condition for the system to complete the operation. Although the vast majority of informational acquisition comes from the visual system, human acquisition and understanding of force and haptic information occupy 2/3 of the brain resources. Therefore, the force perception and interaction system is one of the most complex and comprehensive perception methods. How to efficiently and reliably acquire and understand the force interaction between the robot and the working environment is an urgent need for intelligent robots to achieve reasonable human-machine interaction and intelligent control. For example, when a collaborative robot equipped with a force perception system completes human-machine collaborative tasks such as zero-force teaching and flexible control, the control system of the collaborative robot will adjust its state in time according to the interaction in order to take into account the position servo stiffness of the multi-degree-of-freedom robot control system and the flexibility of the interaction between the collaborative robot and the collaborators. Therefore, the achievement of active compliance control relies on the force perception, i.e., the force/torque feedback information of the multi-component force sensing system, with which the robotic system can complete the traction follow-up, space curve/surface tracking, constant force operation, flexible assembly, and other efficient motion control strategies.

1.1What is a Multi-Component Force Sensing System?

A force sensing system can obtain the interaction force between the robot and the external environment during operation. It is one of the most important perceptions of intelligent robots. Force sensing systems with multi-component perception capability can simultaneously sense the force or moment information in two or more directions in the Cartesian coordinate system, and then realize the information perception such as force, touch, tactile, and slip of the manipulations. Specifically, a six-component force can monitor six components of force terms along the x-, y-, and z-axis (Fx, Fy, and Fz) and the torque terms about x-, y-, and z-axis (Mx, My, and Mz) simultaneously. Force and torque information is always adopted as feedback to obtain a closed-loop control system. As shown in Fig 1.1, the manipulation force and torque between the robot and environment are detected by the multi-component force sensing system, which is used to process the force and position control, i.e., a strategy of robot compliance control.

Figure 1.1Multi-Component F/T Sensing Systems in Force Servo Control Strategy for Robot.

The measurement chain of multi-component force sensing systems consists of several elements, regardless of the adopted principles. Compared to force sensors, the multi-component force sensing systems are characterized by:

• Multi-component force transducer consists of an elastic structure and corresponding measuring elements. The applied load (force and/or torque along an arbitrary axis) acts on the elastic structure, and the measuring element and circuit will transform corresponding physic variations (such as wavelength shift, displacement, strain, potential, etc.) occurred on the elastic structure into the electrical quantity.
• The obtained electrical quantities such as changes in voltage and current are usually small; therefore, instrumentations with amplification function are adopted, which are always placed close to the measuring circuit.
• Data acquisition devices with functions such as analog-to-digital conversion, signal conditioning (filtering, isolation, temperature compensation, linearization, creep correction, etc.) are equipped as the interface between the multi-component force transducer and a computer or an embedded microcomputer system.
• The computer or microcomputer system is adopted to processing (calculation, calibration, and software filtering), storing, and visualizing the measured force information.

1.2Classification of Multi-Component Force Sensing Systems

The earliest detection methods used in force sensing systems are capacitive, resistive strain, and piezoelectric. With the continuous development of detection and sensing technology, more and more detection methods such as fiber grating, inductive, pneumatic, and electromagnetic types are used in force sensing systems. The advantages and disadvantages of various methods (as shown in Table 1.1) determine their applications in different situations.

TABLE 1.1 Disadvantages and Advantages of Different Force Sensing Method

Sensing Principle	Transduction Effect	Advantages	Disadvantages
Magnetoelectric	hall effect	wide dynamic range; low power consumption; high reliability	poor interchangeability; large nonlinear error; low resolution
Capacitive	capacitance variation due to a load	high sensitivity and resolution; large bandwidth; robustness; drift-free; durability;	complex electronic circuits; stray capacitance; edge effect
Resistive	conductivity variation due to a load	theoretical maturity; adjustable resolution; high reliability; maintenance-free	higher power consumption; rigid and fragile; scarce reproducibility
Inductive	magnetic coupling variation due to a load	high sensitivity and resolution; linear output;	lower-frequency response; poor reliability
Optoelectronic	refractive index variation due to a load	good reliability; wide detection range; noncontact	non-conformable; hard to construct dense arrays
Piezoelectric	piezoelectric effect	High-frequency response; higher accuracy; high sensitivity and dynamic range; high stiffness	charge leakages; poor spatial resolution; deteriorations of voltages or drifts in the presence of static forces

Among various principles for multi-component force sensing systems, the most popular approach relies on resistive strain due to its characters such as theoretical maturity, simple processing circuit, adjustable resolution, and high reliability. Another popular approach to measure multi-component is the capacitive method, which shows high resolution, excellent durability, and wide frequency bandwidth. Piezoelectric force sensing systems with piezoelectric effect have received considerable attention due to its advantages such as wide detection range, superior stiffness, high-frequency response, and accuracy. Nowadays, more and more force sensing systems based on metal foil strain gauge are replaced with piezoresistive-based approaches, which feature with increased gauge factor and higher sensitivity. State-of-the-art force sensing systems adopt Fiber Bragg Grating (FBG) or other optoelectronic approaches to detect force and torque with good reliability, wide detection range, and Magnetic Resonance Imaging (MRI) compatibility.

1.3State of the Art and Trends in Multi-Component Force Sensing Systems

As shown in Table 1.2, the research and development of multi-component force sensing systems have been experiencing steady and rapid growth during the past decades. Since 1980, force sensing systems have played an important role in the development and application of intelligent manufacturing and intelligent equipment such as robot-assisted surgical robots, flexible assembly systems, automatic manipulator, cutting force detection, medical-aided rehabilitation training system, etc.

TABLE 1.2 Count of Papers Related Multi-Component Force Sensing Systems from 1980

Table 1.3 summarizes some collections of contributio...