Intro to control of movement (w1) Flashcards
Why is movement important?
-Movement Scientist’s Perspective -> The brain exists for movement and it is specialised in movement. If we understand movement, we understand the brain.
-Thinking is movement confined to the brain – Arvid Carlsson
-We have a brain for one reason and one reason only – and that’s to produce adaptable and complex movement – Daniel Wolpert
What is movement ease?
-> We do not recognise the difficulty of movement control. Complicated high-level control strategies are used by our brain, even when we are thought-lessly doing simple motor tasks
What are empirical observations
-Fitt’s law and Two-Third power law
-Empirical observations (Fitt’s Law) –> If you need accuracy, you become slow. A highly precise relationship can be found between movement duration and Log (2A/W). This relationship is not limited to specific body parts or specific movement – this rule is very general.
-Empirical Observations (Two-Third Power Law) -> If you are making a curved movement you become slow – slower when more curved. Curvature (larger is flatter) and velocity may have a positive relationship. A high precise relationship can be found between curvature and velocity – power of 2/3 of curvature is proportional to velocity. The relationship is not limited to specific body parts of specific movement e.g. found in running and dancing etc.
What are the key problems that a brain (as a robot engineer) needs to solve?
-Localisation and Planning e.g. through coordinates
-Execution and control e.g. through a joint torque
-Modelling and Simulation
What is the space, coordinates, coordinate frames and coordinate transformations?
-Space -> Set (of points) with some added structures e.g. plane: 2 dimensional space. There are 2 representative spaces used in robotics (and motor control).
-Coordinate system -> Set of numbers (called coordinates) that uniquely determine a point in space. A single space can have multiple coordinate systems. Also called coordinate frame/ reference frame
-Egocentric coordinate system -> Coordinate system attached to our body
-Allocentric -> Coordinate system attached to external world (or object)
-Coordinate transformation -> Transformation between different coordinate systems
What is forward/ inverse kinematics, redundancy>
-Forward/ inverse kinematics ->
-Redundancy in Inverse kinematics -> Inverse kinematics can have multiple solutions
What are forward/ inverse dynamics?
-Linear v Angular Kinematics (distances vs angles)
-Linear v Angular Kinetics (forces vs torques)
-Inverse dynamics -> How much torques (eventually, muscle forces) are required to produce certain movement of objects?
-Forward dynamics -> If certain torques (originally, muscle forces) are produced, what is the resultant movement of the objects
What is the relationship between kinematics and dynamics: Newtons second law?
-Newton’s second law defines the relationship between kinematics and dynamics. The equation can be applied to complex systems where F and a are vectors (of forces and torques) and M is a matrix (linear matrix)
-Equation is on 1st lecture notes
Advantages and disadvantages of feedforward (open-loop), pre-determined actions:
+ => Movement can be controlled without processing any external information (good for fast movement
- -> No flexibility to environmental changes and High cost of planning, no generalisation
Advantages and disadvantages of feedback (closed-loop), case-by-case actions:
+ -> Flexible (deals with unexpected events), Robust (control error does not accumulate over time), General (control is variant to starting or goal position
- -> Time-consuming, controller can be unstable and can also become unstable when feedbacks are delayed
What is variability?
-> Even when the same movement is repeated, controller behaviours under uncertainties result different movement patterns. By taking a closer look at the variability patterns, we can get a sense of the brain’s control strategy.
