Robotics 2 Actuators & Sensors

From @VergilOP

Lecture 2 - Actuators & Sensors

Learning Objectives

Objectives:

• Different Types of Actuators 不同类型的执行器
• Sensors 传感器

Actuators

Three commonly used actuator types:

• Electromagnetic(The most common types of actuators) 电磁
• Hydraulic 液压
• Pneumatic 气动

Electromagnetic Actuators 电磁执行器

• Brushed DC Motor 有刷直流电动机
  • Current flowing through armature generates a magnetic field and permanent magnets torque the armature
    通过电枢的电流产生磁场，永久磁铁扭转电枢
    • Advantages: Provicdes variable speeds, low-cost
      优点：提供可变速度，成本低
    • Disadvantages: Brush wear out, low precision
      缺点：刷子磨损，精度低
• Brushless DC Motor 无刷直流电动机
  • Armature is fixed, and permanent magnets rotate
    电枢固定，永久磁铁旋转
    • Advantages: Efficiency, Low noise, Cooling, Water-resistant
      优点：效率高、噪音低、散热、耐水
    • Disadvantages: low percision, costly
      缺点：精度低，成本高
• Stepper Motor 步进电动机
  • Brushless, synchronous motor that moves in discrete steps
    无刷、同步电机，以离散步进运动
    • Advantage: Precise, quantized control without feedback 优点：精确、量化控制，无需反馈
    • Disadvantages: Slow and moves in discrete steps, expensive 缺点：速度慢，以离散步进移动，成本高

Hydraulic Actuators 液压执行器

• Cylinders(linear actuators): 气缸（线性执行器）
  • Advantages:
    • Very powerful that offer very large force capability, but expensive 非常强大，提供极大的力输出，但成本高
    • High power-to-weight ratio 功率与重量比高
  • Drawbacks:
    • Their power supplies are bulky and heavy 电源体积大且沉重
    • Oil leakage 漏油问题

• Motors(rotary actuators) 马达（旋转执行器）

• Integrated Smart Hydraulic Actuator 集成智能液压执行器
  • Usual hydraulic actuator-valve configuration 常见的液压执行器-阀门配置

Pneumatic Actuators 气动执行器

• Cylinders(linear actuators) 气缸（线性执行器）

• Motors(rotary actuators) 马达（旋转执行器）

Sensors

Motivation

A robot would be easily controlled if a complete model of the environment was available for the robot, and if tis actuators could execute motion commands perfectly relative to this model
如果机器人拥有完整的环境模型，并且其执行器能够相对于该模型完美执行运动命令，则机器人将更容易控制。

Robotic sensor classsification

• Proprioceptive 本体感知
  • Internal state of the robot 机器人的内部状态
  • Measures values (e.g. wheels position, joint angle, battery level, etc)
• Exteroceptive 外感知
  • External state of the system 系统的外部状态
  • Observing environment, detecting objects, etc
• Active 主动
  • Emits energy(e.g. radar)
• Passive 被动
  • Receives energy(e.g. camera)
• Real-world Characteristics of sensors
  • Sensitivity: Ratio of output change to input change
    灵敏度：输出变化与输入变化的比率
  • Error/Accuracy: Difference between the sensor’s output and the true value
    误差/准确度：传感器输出与真实值之间的差异
    • Systematic/Deterministic Error: Caused by factors that can be modelled(in theory), e.g., calibration of a laser sensor
      系统/确定性误差：由可建模的因素引起（理论上），如激光传感器的校准
    • Random Error: e.g., hue instability of camera, black level noise of camera
      随机误差：如相机色调不稳定、相机的黑电平噪声
  • Reproducibility: Reproducibility of sensor results
    再现性：传感器结果的可重复性

Various sensors overview

• A simple On/Off switch
• Titl sensor(mercury titl) 倾斜传感器（汞倾斜）
• Dual axis inclinometer 双轴倾斜仪
• Potentiometer 电位器
• Bumpers 缓冲器
  • Mechanical switches
• Light sensors
  • Photoresistors, light dependent resistors(LDR)
  • Phototransistors 光电晶体管
• Thermal sensor 热传感器
  • Thermal resistor
  • Temperature sensors
    • Analogue
    • Digital
• Proximity sensors 接近传感器
  • Non-contact
  • Devices that can be used in areas that are near to an object to be sensed
  • Different types of Proximity Sensors
    • Infrared
    • Ultrasonic
    • Inductive 电感
    • Capacitive 电容
• Position Sensors
  • Potentiometer 电位器
  • Resolver 解算器
  • Optical Encoders
    • Relative position
    • Absolue position
• Heading sensors: 方位传感器
  • Heading sensors can be proprioceptive(gyroscope, inclinometer) or exteroceptive(compass)
    方位传感器可以是本体感知（陀螺仪、倾角仪）或外感知（指南针）
  • Used to determine the robots orientation and inclination
    用于确定机器人的方位和倾斜角
• Accelerometer
  • be made to sense acceleration by simply measuring the force on a mass
• Gyroscope 陀螺仪
  • Heading seonsors for measuring and to keep the orientation to a fixed frame
    用于测量和保持相对于固定框架的方向的方位传感器
  • Two methods:
    • Mechanical(flywheel)
    • Electronic

Components used for Manipulators

• Components in a joint:
  • Moters(electric or hydraulic)
  • Moter Encoders
    • Angle(joint angle)
    • Displacement sensor 位移传感器
  • Gearbox 齿轮箱