cortex: thesis/cortex.org comparison

comparison thesis/cortex.org @ 481:6e68720e1c13

add muscles. so STRONG right now.

author	Robert McIntyre <rlm@mit.edu>
date	Fri, 28 Mar 2014 23:30:39 -0400
parents	ad76b8b05517
children	074eadc919fe

comparison

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-:ad76b8b05517
+:6e68720e1c13
 #+caption: pitch, and White is roll.
 #+name: proprio
 #+ATTR_LaTeX: :width 11cm
 [[./images/proprio.png]]
-** Muscles are both effectors and sensors
+** COMMENT Muscles are both effectors and sensors
+Surprisingly enough, terrestrial creatures only move by using
+torque applied about their joints. There's not a single straight
+line of force in the human body at all! (A straight line of force
+would correspond to some sort of jet or rocket propulsion.)
+In humans, muscles are composed of muscle fibers which can contract
+to exert force. The muscle fibers which compose a muscle are
+partitioned into discrete groups which are each controlled by a
+single alpha motor neuron. A single alpha motor neuron might
+control as little as three or as many as one thousand muscle
+fibers. When the alpha motor neuron is engaged by the spinal cord,
+it activates all of the muscle fibers to which it is attached. The
+spinal cord generally engages the alpha motor neurons which control
+few muscle fibers before the motor neurons which control many
+muscle fibers. This recruitment strategy allows for precise
+movements at low strength. The collection of all motor neurons that
+control a muscle is called the motor pool. The brain essentially
+says "activate 30% of the motor pool" and the spinal cord recruits
+motor neurons until 30% are activated. Since the distribution of
+power among motor neurons is unequal and recruitment goes from
+weakest to strongest, the first 30% of the motor pool might be 5%
+of the strength of the muscle.
+My simulated muscles follow a similar design: Each muscle is
+defined by a 1-D array of numbers (the "motor pool"). Each entry in
+the array represents a motor neuron which controls a number of
+muscle fibers equal to the value of the entry. Each muscle has a
+scalar strength factor which determines the total force the muscle
+can exert when all motor neurons are activated. The effector
+function for a muscle takes a number to index into the motor pool,
+and then "activates" all the motor neurons whose index is lower or
+equal to the number. Each motor-neuron will apply force in
+proportion to its value in the array. Lower values cause less
+force. The lower values can be put at the "beginning" of the 1-D
+array to simulate the layout of actual human muscles, which are
+capable of more precise movements when exerting less force. Or, the
+motor pool can simulate more exotic recruitment strategies which do
+not correspond to human muscles.
+This 1D array is defined in an image file for ease of
+creation/visualization. Here is an example muscle profile image.
+#+caption: A muscle profile image that describes the strengths
+#+caption: of each motor neuron in a muscle. White is weakest
+#+caption: and dark red is strongest. This particular pattern
+#+caption: has weaker motor neurons at the beginning, just
+#+caption: like human muscle.
+#+name: muscle-recruit
+#+ATTR_LaTeX: :width 7cm
+[[./images/basic-muscle.png]]
+*** Muscle meta-data
+#+caption: Program to deal with loading muscle data from a blender
+#+caption: file's metadata.
+#+name: motor-pool
+#+begin_listing clojure
+#+BEGIN_SRC clojure
+(defn muscle-profile-image
+"Get the muscle-profile image from the node's blender meta-data."
+[#^Node muscle]
+(if-let [image (meta-data muscle "muscle")]
+(load-image image)))
+(defn muscle-strength
+"Return the strength of this muscle, or 1 if it is not defined."
+[#^Node muscle]
+(if-let [strength (meta-data muscle "strength")]
+strength 1))
+(defn motor-pool
+"Return a vector where each entry is the strength of the \"motor
+neuron\" at that part in the muscle."
+[#^Node muscle]
+(let [profile (muscle-profile-image muscle)]
+(vec
+(let [width (.getWidth profile)]
+(for [x (range width)]
+(- 255
+(bit-and
+0x0000FF
+(.getRGB profile x 0))))))))
+#+END_SRC
+#+end_listing
+Of note here is =motor-pool= which interprets the muscle-profile
+image in a way that allows me to use gradients between white and
+red, instead of shades of gray as I've been using for all the
+other senses. This is purely an aesthetic touch.
+*** Creating muscles
+#+caption: This is the core movement functoion in =CORTEX=, which
+#+caption: implements muscles that report on their activation.
+#+name: muscle-kernel
+#+begin_listing clojure
+#+BEGIN_SRC clojure
+(defn movement-kernel
+"Returns a function which when called with a integer value inside a
+running simulation will cause movement in the creature according
+to the muscle's position and strength profile. Each function
+returns the amount of force applied / max force."
+[#^Node creature #^Node muscle]
+(let [target (closest-node creature muscle)
+axis
+(.mult (.getWorldRotation muscle) Vector3f/UNIT_Y)
+strength (muscle-strength muscle)
+pool (motor-pool muscle)
+pool-integral (reductions + pool)
+forces
+(vec (map  #(float (* strength (/ % (last pool-integral))))
+pool-integral))
+control (.getControl target RigidBodyControl)]
+;;(println-repl (.getName target) axis)
+(fn [n]
+(let [pool-index (max 0 (min n (dec (count pool))))
+force (forces pool-index)]
+(.applyTorque control (.mult axis force))
+(float (/ force strength))))))
+(defn movement!
+"Endow the creature with the power of movement. Returns a sequence
+of functions, each of which accept an integer value and will
+activate their corresponding muscle."
+[#^Node creature]
+(for [muscle (muscles creature)]
+(movement-kernel creature muscle)))
+#+END_SRC
+#+end_listing
+=movement-kernel= creates a function that will move the nearest
+physical object to the muscle node. The muscle exerts a rotational
+force dependent on it's orientation to the object in the blender
+file. The function returned by =movement-kernel= is also a sense
+function: it returns the percent of the total muscle strength that
+is currently being employed. This is analogous to muscle tension
+in humans and completes the sense of proprioception begun in the
+last section.
 ** =CORTEX= brings complex creatures to life!
 ** =CORTEX= enables many possiblities for further research

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comparison thesis/cortex.org @ 481:6e68720e1c13