Purpose: Learning basic knowledge of robotics
Lecture: CS223A, Stanford University
Material: Copy from Stanford
Video clips: https://www.youtube.com/watch?v=0yD3uBshJB0&list=PL65CC0384A1798ADF
=== Lecture 1: Spatial Description ===
General Manipulator: Robot Arm, using Revolute joint, Prismatic joint
- Robot Arm: base, link, joint, end-effector
- Revolute joint: Rotation movement, 1 Degree of Fredom(DoF)
- Prismatic joint: Linear movement, 1 DoF
- Denote joint type using ε(0 for revolute, 1for prismatic)
Discription of body1 (9 parameters)
- Link location: 3 points (Each point has 3 parameters)
Discription of body2 (6 parameters)
- Body orientation: 3 parameter
- Point on the body: 3 parameter
=> Robot arm(n:links, 1: base) has n DoF
Configuration Representation
There is no universial agreement in the field of robotics as to what is the best orientation representation.
Because each representation hase advantages and shortcomings
- Euler angle representation: ZYX, angle(α, β, γ)
- Fixed angle representation: XYZ, angle(γ, β, α)
- Inverse of an orientation representation
=== Lecture 2: Direct Kinematics ===
- Independent of the structure of the manipulator
- A set of parameters specific to each manipulator
- ex) rotation, translation, link of manipulator
- Manipulator: Consist of a chain of links from base
- Consecutive links are connected by joints which exert the degree of freedom.
- link length(a): length along the common normal from axis (i-1) to axis i
- link twist(α): angle between this parallel line and axis (i-1)
- link offset(θ): distance alont the line on axis i between the common normal for link (i-1) and common normal for link i
- joint angle(d): angle between the two common normal for link (i-1) and common normal for link i
- Revolute joint: joint angle(variable), link offset(constant)
- Prismatic joint: joint angle(constant), link offset(variable)
- d, θ: describe the link's connection
Conventions for First and Last Link
- Once robot structure is set link length & link twist is determined.
- a(i) and α(i) depend on joint axes i and i+1
Axes 1 to n: determined => a(1), a(2), ,,,, a(n-1) and α(1), α(2), ,,,,a(n-1)
- d(i) and θ(i) depend on
Attaching Frames to links
- ex1) RRR (Revolute-Revolute-Revolute) Manipulator
- ex2) RPRR (Revolute-Prismatic-Revolute-Revolute) Manipulator
- Show how to calculate matrix about D-H parameter
- Refer: https://wikimedia.org/api/rest_v1/media/math/render/svg/6963d0c47a3a894ff0719c8df348d188b996074e
Kinematics of Manipulators
- Example of robot arm (Stanford Scheinman Arm)
- Refer: http://infolab.stanford.edu/pub/voy/museum/pictures/display/robots/StanfordArm.jpg
Direct(forward) Kinematics
- Mapping between the joint space of dimension n and the task space of manipulator of dimension m
- Called the "Geometric Model of the manipulator"
(It is determinded solely by knowing the geometry of manipulator)
- q(i) = ε'(i)θ(i) + ε(i)d(i)
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