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fleshing out text in muscle.org
author Robert McIntyre <rlm@mit.edu>
date Tue, 14 Feb 2012 03:16:50 -0700
parents 66fbab414d45
children 2fdcbe8185b1
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259:7cac5ef852e3 260:959127e21f81
1 #+title: Movement! 1 #+title: Simulated Muscles
2 #+author: Robert McIntyre 2 #+author: Robert McIntyre
3 #+email: rlm@mit.edu 3 #+email: rlm@mit.edu
4 #+description: muscles for a simulated creature 4 #+description: muscles for a simulated creature
5 #+keywords: simulation, jMonkeyEngine3, clojure 5 #+keywords: simulation, jMonkeyEngine3, clojure
6 #+SETUPFILE: ../../aurellem/org/setup.org 6 #+SETUPFILE: ../../aurellem/org/setup.org
7 #+INCLUDE: ../../aurellem/org/level-0.org 7 #+INCLUDE: ../../aurellem/org/level-0.org
8 8
9 9
10 * Muscles
11
10 Surprisingly enough, terristerial creatures only move by using torque 12 Surprisingly enough, terristerial creatures only move by using torque
11 applied about their joints. There's not a single straight line of 13 applied about their joints. There's not a single straight line of
12 force in the human body at all! (A straight line of force would 14 force in the human body at all! (A straight line of force would
13 correspond to some sort of jet or rocket propulseion.) 15 correspond to some sort of jet or rocket propulsion.)
14 16
17 *(next paragraph is from memory and needs to be checked!)*
15 18
16 Here's how motor-control/ proprioception will work: Each muscle is 19 In humans, muscles are composed of millions of sarcomeres, which can
17 defined by a 1-D array of numbers (the "motor pool") each of which 20 contract to exert force. A single motor neuron might control 100-1,000
18 represent muscle fibers. A muscle also has a scalar :strength factor 21 sarcomeres. When the motor neuron is engaged by the brain, it
19 which determines how strong the muscle as a whole is. The effector 22 activates all of the sarcomeres to which it is attached. Some motor
20 function for a muscle takes a number < (count motor-pool) and that 23 neurons command many sarcomeres, and some command only a few. The
21 number is said to "activate" all the muscle fibers whose index is 24 spinal cord generally engages the motor neurons which control few
22 lower than the number. Each fiber will apply force in proportion to 25 sarcomeres before the motor neurons which control many sarcomeres.
23 its value in the array. Lower values cause less force. The lower 26 This recruitment stragety allows for percise movements at low
24 values can be put at the "beginning" of the 1-D array to simulate the 27 strength. The collection of all motor neurons that control a muscle is
25 layout of actual human muscles, which are capable of more percise 28 called the motor pool. The brain essentially says "activate 30% of the
26 movements when exerting less force. 29 motor pool" and the spinal cord recruits motor neurons untill 30% are
30 activated. Since the distribution of power among motor neurons is
31 unequal and recruitment goes from weakest to strongest, 30% of the
32 motor pool might be 5% of the strength of the muscle.
33
34 My simulated muscles follow a similiar design: Each muscle is defined
35 by a 1-D array of numbers (the "motor pool"). Each number represents a
36 motor neuron which controlls a number of sarcomeres equal to the
37 number. A muscle also has a scalar :strength factor which determines
38 the total force the muscle can exert when all motor neurons are
39 activated. The effector function for a muscle takes a number to index
40 into the motor pool, and that number "activates" all the motor neurons
41 whose index is lower or equal to the number. Each motor-neuron will
42 apply force in proportion to its value in the array. Lower values
43 cause less force. The lower values can be put at the "beginning" of
44 the 1-D array to simulate the layout of actual human muscles, which
45 are capable of more percise movements when exerting less force. Or,
46 the motor pool can simulate more exoitic recruitment strageties which
47 do not correspond to human muscles.
48
49 This 1D array is defined in an image file for ease of
50 creation/visualization. Here is an example muscle profile image.
51
52 #+caption: A muscle profile image that describes the strengths of each motor neuron in a muscle. White is weakest and dark red is strongest. This particular pattern has weaker motor neurons at the beginning, just like human muscle.
53 [[../images/basic-muscle.png]]
54
55 * Blender Meta-data
56
57 In blender, each muscle is an empty node whose top level parent is
58 named "muscles", just like eyes, ears, and joints.
59
60 These functions define the expected meta-data for a muscle node.
27 61
28 #+name: movement 62 #+name: movement
29 #+begin_src clojure 63 #+begin_src clojure
30 (ns cortex.movement 64 (in-ns 'cortex.movement)
31 "Give simulated creatures defined in special blender files the power
32 to move around in a simulated environment."
33 {:author "Robert McIntyre"}
34 (:use (cortex world util sense body))
35 (:use clojure.contrib.def)
36 (:import java.awt.image.BufferedImage)
37 (:import com.jme3.scene.Node)
38 (:import com.jme3.math.Vector3f)
39 (:import com.jme3.bullet.control.RigidBodyControl))
40
41 (defn muscle-profile
42 "Return a vector where each entry is the strength of the \"motor
43 pool\" at that part in the muscle."
44 [#^BufferedImage profile]
45 (vec
46 (let [width (.getWidth profile)]
47 (for [x (range width)]
48 (- 255
49 (bit-and
50 0x0000FF
51 (.getRGB profile x 0)))))))
52 65
53 (defvar 66 (defvar
54 ^{:arglists '([creature])} 67 ^{:arglists '([creature])}
55 muscles 68 muscles
56 (sense-nodes "muscles") 69 (sense-nodes "muscles")
57 "Return the children of the creature's \"muscles\" node.") 70 "Return the children of the creature's \"muscles\" node.")
58 71
59 (defn movement-fn 72 (defn muscle-profile-image
73 "Get the muscle-profile image from the node's blender meta-data."
74 [#^Node muscle]
75 (if-let [image (meta-data muscle "muscle")]
76 (load-image image)))
77
78 (defn muscle-strength
79 "Return the strength of this muscle, or 1 if it is not defined."
80 [#^Node muscle]
81 (if-let [strength (meta-data muscle "strength")]
82 strength 1))
83
84 (defn motor-pool
85 "Return a vector where each entry is the strength of the \"motor
86 neuron\" at that part in the muscle."
87 [#^Node muscle]
88 (let [profile (muscle-profile-image muscle)]
89 (vec
90 (let [width (.getWidth profile)]
91 (for [x (range width)]
92 (- 255
93 (bit-and
94 0x0000FF
95 (.getRGB profile x 0))))))))
96 #+end_src
97
98 Of note here is =(motor-pool)= which interprets the muscle-profile
99 image in a way that allows me to use gradients between white and red,
100 instead of shades of gray as I've been using for all the other
101 senses. This is purely an aesthetic touch.
102
103 * Creating Muscles
104 #+begin_src clojure
105 (defn movement-kernel
60 "Returns a function which when called with a integer value inside a 106 "Returns a function which when called with a integer value inside a
61 running simulation will cause movement in the creature according 107 running simulation will cause movement in the creature according
62 to the muscle's position and strength profile. Each function 108 to the muscle's position and strength profile. Each function
63 returns the amount of force applied / max force." 109 returns the amount of force applied / max force."
64 [#^Node parts #^Node muscle] 110 [#^Node creature #^Node muscle]
65 (let [target (closest-node parts muscle) 111 (let [target (closest-node creature muscle)
66 axis 112 axis
67 (.mult (.getWorldRotation muscle) Vector3f/UNIT_Y) 113 (.mult (.getWorldRotation muscle) Vector3f/UNIT_Y)
68 strength (meta-data muscle "strength") 114 strength (muscle-strength muscle)
69 image-name (read-string (meta-data muscle "muscle")) 115
70 image (load-image image-name) 116 pool (motor-pool muscle)
71 fibers (muscle-profile image) 117 pool-integral (reductions + pool)
72 fiber-integral (reductions + fibers)
73 force-index 118 force-index
74 (vec (map #(float (* strength (/ % (last fiber-integral)))) 119 (vec (map #(float (* strength (/ % (last pool-integral))))
75 fiber-integral)) 120 pool-integral))
76 control (.getControl target RigidBodyControl)] 121 control (.getControl target RigidBodyControl)]
77 (fn [n] 122 (fn [n]
78 (let [pool-index (max 0 (min n (dec (count fibers)))) 123 (let [pool-index (max 0 (min n (dec (count pool))))
79 force (force-index pool-index)] 124 force (force-index pool-index)]
80 (.applyTorque control (.mult axis force)) 125 (.applyTorque control (.mult axis force))
81 (float (/ force strength)))))) 126 (float (/ force strength))))))
82
83 127
84 (defn movement! 128 (defn movement!
85 "Endow the creature with the power of movement. Returns a sequence 129 "Endow the creature with the power of movement. Returns a sequence
86 of functions, each of which accept an integer value and will 130 of functions, each of which accept an integer value and will
87 activate their corresponding muscle." 131 activate their corresponding muscle."
88 [#^Node creature] 132 [#^Node creature]
89 (for [muscle (muscles creature)] 133 (for [muscle (muscles creature)]
90 (movement-fn creature muscle))) 134 (movement-kernel creature muscle)))
135 #+end_src
91 136
137 =(movement-kernel)= creates a function that will move the nearest
138 physical object to the muscle node. The muscle exerts a rotational
139 force dependant on it's orientation to the object in the blender
140 file. The function returned by =(movement-kernel)= is also a sense
141 function: it returns the percent of the total muscle strength that is
142 currently being employed. This is analogous to muscle tension in
143 humans and completes the sense of proprioception begun in the last
144 post.
145
146 * Visualizing Muscle Tension
147 Muscle exertion is a percent of a total, so the visulazation is just a
148 simple percent bar.
149
150 #+begin_src clojure
92 (defn movement-display-kernel 151 (defn movement-display-kernel
93 "Display muscle exertion data as a bar filling up with red." 152 "Display muscle exertion data as a bar filling up with red."
94 [exertion] 153 [exertion]
95 (let [height 20 154 (let [height 20
96 width 300 155 width 300
106 (defn view-movement 165 (defn view-movement
107 "Creates a function which accepts a list of muscle-exertion data and 166 "Creates a function which accepts a list of muscle-exertion data and
108 displays each element of the list to the screen." 167 displays each element of the list to the screen."
109 [] 168 []
110 (view-sense movement-display-kernel)) 169 (view-sense movement-display-kernel))
111
112 #+end_src 170 #+end_src
113 171
172 * Adding Touch to the Worm
114 173
174
175 * Headers
176 #+name: muscle-header
177 #+begin_src clojure
178 (ns cortex.movement
179 "Give simulated creatures defined in special blender files the power
180 to move around in a simulated environment."
181 {:author "Robert McIntyre"}
182 (:use (cortex world util sense body))
183 (:use clojure.contrib.def)
184 (:import java.awt.image.BufferedImage)
185 (:import com.jme3.scene.Node)
186 (:import com.jme3.math.Vector3f)
187 (:import com.jme3.bullet.control.RigidBodyControl))
188 #+end_src
115 189
116 190
117 191
118 * COMMENT code generation 192 * COMMENT code generation
119 #+begin_src clojure :tangle ../src/cortex/movement.clj 193 #+begin_src clojure :tangle ../src/cortex/movement.clj