Flashcards in Term 1 Revision Deck (39)
What is robotics? What are robots?
Robotics is an interdisciplinary branch of engineering that includes mech-eng, elec-eng, computer science and others. Deals with the design, construction, operation and use of robots
What are robots?
An electromechanical device with multiple degrees-of-freedom that is programmable to accomplish a variety of tasks
What are degrees-of-freedom?
The number of independent motions a device can make. For an arm with three joints that can swivel at the bottom would have 4 degrees of freedom
What are: manipulators, enf-effectors
Electromechanical devices capable of interacting with their environment.
The tool, gripper or other device mounted at the end of a manipulator for accomplishing useful tasks
What is workspace?
The volume in space that a robot's end-effector can reach, both in position and orientation
What do accuracy and repeatablity mean in terms of robotics?
Accuracy: ability of a robot to go to the desired position with the minimal error
Repeatability: ability of a robot to repeatably position itself when asked to perform a task multiple times
Three ways to measure a robots performance
Working volume-the space in which the robot operates.
Larger volume costs more but makes the robot more useful
Speed/acceleration: faster speed is better but can increase cost and is limited by task the robots doing (welding etc)
Resolution: smallest step a robot can take. Often a speed tradeoff
Determinant of 2x2 matrix and how to work out 3x3?
For 3x3 divide the bottom two rows into three 2x2 and determinant those, multipying them by the one not near them
Inverse of 2x2 matrix
Whats a singular matrix?
Inverse of matrix A:
1/det(A) [d -b]
A singular matrix is a matrix with a determinant of zero
Standard rotation matrix form and how to tell if a matrix is a rotational one?
The determinant will be one
What are joints and links?
Joints: enables linear or rotational motion of adjoining members
Links: rigid members between two joints
Prismatic joints:defintion and types of joints
Prismatic: sliding/linear joints. Called prismatic because the cross section of the joint is considered a prism
Linear (L) joint: link that slides in and out of a tube
Orthogonal (O) joint: T shaped joint that moves along a link
Revolute joints: definition and types of joints
Only permit angular motion between links.
Rotational (R) joint: rotation around an axis perpendicular to adjoining links. Imagine your elbow
Twisting (T) joint: rotation takes place about an axis parallel to both adjoining links. Imagine your wrist
Revolving (V) joint: Input link is parallel and output link is perpendicular to rotational axis. Imagine rotating your shoulder with your elbow at right angles.
Two other types of complex joints we might need to know?
Universal (U) and spherical (S)
Robot made of serial connections of joints
No kinematic constaint in each joint motion (basically its not attached to anything that would constrain it)
Joints can be arranged in parallel as well as in series.
Can form a 'closed kinematic chain' and thus some joints must conform to a certain geometric constraint
Cartesian configuration definition, examples and pros/cons
Robots consisting of links connected by linear joints
Usually three joints to cover all cartesian axis
Used for pick and place work, assembly operations and arc welding
Easy to program, most rigid structure for given length (can lift a lot)
Needs a lot of space, can only reach in front of itself
Cylindrical configuration definition, examples and pros/cons
Robots with one rotary joint at the base and linear joints to connect the other links
Used for die-casting machines, handling machine tools and spot welding
Can reach all around itself, easy to program
Linear axes are hard to seal, exposed drives are hard to cover from dusts/liquids
Joint-arm configuration definition, examples and pros/cons
Linkes in arm are connected by rotatory joints. Arm is connected to base with a twisting joint
Used for welding sealing, spray painting and welding
Very flexiable, any point in total volume can be reached
Very hard to program, low accuracy
Is a rotational matrix rotating clockwise or counter-clockwise?
θ>0, rotate counter-clockwise
θ<0, rotate clockwise
Whats kinematics? Whats the difference between forward and backward kinematics?
Geometry of motion, provides tools to describe the structure and behaviour of robot mechanisms
FK: uses actuation angles to derive the end-effector location
BK: use end-effector location to derive actuation angles
Forward kinematics equation-use two links and the coordinates of the end-effctor as an example
x=L1*cos(θ1) + L2*cos(θ1+θ2)
y=L1*sin(θ1) + L2*sin(θ1+θ2)
Φ (final angle of effector) = θ1+θ2
What do domain and range mean in terms of kinematics?
Domain: set of possible θ's (there may be joint limits)
Range: set of points that the end-effector can reach
Working out constraints in kinematics
Use this if there's parallel linkage, i.e. if two or more sets of links and joints are connected to the same joint.
Write equations describing each set of links and joints to the shared joint, then set them equal to each other
Working out inverse kinematics. Equations and what do you need to remember about solution?
Start with four variables: coordinates of final position (Xc, Yc), coordinates of previous joint (Xb, Yc), length of link between them (L3) and final angle of effector (Φ).
Xb = Xc - L3*cos(Φ)
Yb = Yc - L3*sin(Φ)
There can also be multiple solutions since these problems are nonlinear
How to write a Jacobian matrix?
How to work out when a singularity occurs in a Jacobian matrix?
Top left: -(L1*sin(θ1) + L2*sin(θ1+θ2))
Top right: -L2*sin(θ1+θ2)
Bottom left: L1*cos(θ1) + L2*cos(θ1+θ2)
Bottom right: L2*cos(θ1+θ2)
When θ2 = 0 and π
Point-to-point motion definition and applications
Only the end points are programmed, the path used to connect these points are computed by the controller.
Applications include pick and place, machine loading
Continuous path control definition and applications
In addition to control over end points, the path taken by the end effector can also be controlled.
Controlled by manipulating the joints throughout entire motion via closed loop control
Applications include spray painting, polishing, grinding
The three elements of control systems and what they do
The control: the brain, reads instruction
Current amplifier: recieves orders from brain and sends required signal to the motor
Servo motor: output depends on whether open or closed loop is used
What is Open loop control
Controller is told where output device needs to be
Once signal is sent to motor, it dosn't receive feedback to know if it's reached desired position
Open is cheaper but less accurate than closed loop
What is closed loop control?
Provides feedback to control unit tell it the actual position of the motor.
Position found using an encoder, is compared to desired postion and changed if necessary
Two types of closed loop control, pros/cons
On-off control: system turns on when measured variable falls below threshold, turns off when it rises above threshold.
Low cost but tends to overshoot with low accuracy
Proportional control: control system isn't turned on or off but set to anywhere between 0% to 100%.
Higher cost but more accurate
What does HRI stand for? Give some examples
Human Robot Interaction
Remote interaction: humans and robots are seperated spatially or temporally
Proximate interaction: humans and robots share the same physical space
Human roles in HRI-when are humans needed?
Supervisor-monitor and control overall situation
Operator-deals with software
Mechanic-deals with hardware
Cognitive interaction definition and examples
Interactions related to bi-directional cognitions (inference, planning and action) between human and robot.
Examples include spatial reasoning, anticipation of the future and temporal reasoning
Physical Interaction definition and examples
Interactions related to forces generated between the musculoskeletal system and the body of the robot.
Examples include exoskeletons, prosthetics and HRI in the same environment
Ways for humans and robots to exchange information-three catagorys
Visual: robots use visual displays (lights, screens etc.) Humans use gestures (hand, facial, body)
Audio: robots use natural language and non-speech audio. Humans use natural language
Tactile: robots use haptics (comminicating through touch). Humans use keyboard, mouse ect.
Uses for surgical robotics
Capsule robots for cancer screening and colonoscopy