Notes on Underactuated Robotics
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ยง2.1.1 Test 2iei๐œƒ

2.1.1 Test 2iei๐œƒ

Usually, controlling a system involves using a loop that adjusts the input of the system by observing the state of the system. How exactly the observants affect the input and how to design this relationship to change the system to a desired state is the study of control theory.

The mathematical background consists mainly of nonlinear differential equations and linear algebra.

Mostly, for differential equations, we will consider how the state vector would change given the current state vector and the control input.

Let ๐ฑ be the state vector, and let ๐ฎ be the set of control inputs. Then this relationship is modelled by some function ๐‘“ of ๐ฑ and ๐ฎ with

๐ฑฬ‡=๐Ÿ(๐ฑ,๐ฎ).

In the linear case,

๐ฑฬ‡=๐€๐ฑ+๐๐ฎ.

In many mechanical systems, by virtue of Newtonโ€™s second law, which states that force changes the second-order derivative of position, ๐ชฬˆ, depends on both the generalized positions ๐ช, and the generalized velocities ๐ชฬ‡. Therefore,

๐ชฬˆ=๐Ÿ(๐ช,๐ชฬ‡,๐ฎ),

as a second-order system. The state of a system comprises not only the positions, but their velocities. Then we write that

๐ฑ=(๐ช๐ชฬ‡),and๐ฑ=(๐ชฬ‡๐ชฬˆ)=(๐ชฬ‡๐Ÿ(๐ช,๐ชฬ‡,๐ฎฬ‡)).

If ๐ฎ represents the motor torques (for example), and the generalized positions measure angles, then this is typically written as

๐ชฬˆ=๐Ÿ1(๐ช,๐ชฬ‡)+๐Ÿ2(๐ช,๐ชฬ‡)๐ฎ,(โ€ )

where ๐Ÿ๐Ÿ(โ‹…)โˆˆโ„๐‘š is a vector with dimensionality matching ๐ชโˆˆโ„๐‘š, and ๐Ÿ๐Ÿ is a matrix of dimension ๐‘šร—๐‘›.

Affinity is perceived with respect to the control input ๐ฎโˆˆโ„๐‘› (hence control affine), and the equation above is affine in ๐ฎ since it is a linear transformation of it.

Definition 2.1.1.1 (Much).

Ah vous dirai je maman

Proof.

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โˆซโˆซโˆซโˆซโˆซโˆซโˆซโˆซโˆซโˆซโˆซโˆซd๐‘ฅd๐‘ฅd๐‘ฅd๐‘ฅd๐‘ฅd๐‘ฅd๐‘ฅโ–ก

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๐น=๐‘š๐‘Ž

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๐น=๐‘š๐‘Ž(2.1.1.1)

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๐น=๐‘š๐‘Ž

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๐น=๐‘š๐‘Ž(2.1.1.2)
Solution of a test.

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  1. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magnam aliquam quaerat.
  2. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magnam aliquam quaerat.
  3. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magnam aliquam quaerat. โ–ก

Obviously, in the case that ๐Ÿ2 has more rows (๐‘š) than columns (๐‘›), then the rank of ๐Ÿ2 is at most ๐‘›, whereas the dimensionality of ๐ช, or ๐‘š, is greater than ๐‘›. Thus, in this case the system will always be underactuated. We provide a heuristic or intuitive explanation; since there are less control inputs than the positions we wish to control, we do not have full control of the system. Refer to Definitionย 2.1.1.1Definitionย 2.1.1.1Definitionย 2.1.1.1

Figureย 1: Geometry of the finite subcover of ๐‘‰๐‘›โŠ‚๐‘Š๐‘› for some ๐‘›โˆˆโ„•.

Figureย 1Figureย 2.1Figureย 1

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2

Proof.

sinsinsinsinsinsinsinsinsin(2.1.1.3)
โ€–๐ˆ(๐‘ค1)โˆ’๐ˆ(๐‘ค2)โ€–=(2โ„œ๐”ข๐‘ค1|๐‘ค1|2+1โˆ’2โ„œ๐”ข๐‘ค2|๐‘ค2|2+1)2+(2โ„‘๐”ช๐‘ค1|๐‘ค1|2+1โˆ’2โ„‘๐”ช๐‘ค2|๐‘ค2|2+1)2+(|๐‘ค1|2โˆ’1|๐‘ค1|2+1โˆ’|๐‘ค2|2โˆ’1|๐‘ค2|2+1)2=1(|๐‘ค1|2+1)(|๐‘ค2|2+1)ร—4โ„œ๐”ข[๐‘ค1(|๐‘ค2|2+1)โˆ’๐‘ค2(|๐‘ค1|2+1)]2+4โ„‘๐”ช[๐‘ค1(|๐‘ค2|2+1)โˆ’๐‘ค2(|๐‘ค1|2+1)]2+[(|๐‘ค1|2โˆ’1)(|๐‘ค2|2+1)โˆ’(|๐‘ค2|2โˆ’1)(|๐‘ค1|2+1)]2=2๐œŒ1๐œŒ2|๐‘ค1๐œŒ2โˆ’๐‘ค2๐œŒ1|2+(๐œŒ1โˆ’๐œŒ2)2(where ๐œŒ๐‘–=|๐‘ค๐‘–|2+1)=2๐œŒ1๐œŒ2๐œŒ22(๐œŒ1โˆ’1)+๐œŒ12(๐œŒ2โˆ’1)โˆ’2๐œŒ2๐œŒ1โ„œ๐”ข[๐‘ค1๐‘ค2ฬ…]+(๐œŒ1โˆ’๐œŒ2)2=2๐œŒ1๐œŒ2๐œŒ22๐œŒ1+๐œŒ12๐œŒ2โˆ’2๐œŒ2๐œŒ1โ„œ๐”ข[๐‘ค1๐‘ค2ฬ…]โˆ’2๐œŒ1๐œŒ2(nah)(hello!)=2๐œŒ1๐œŒ2๐œŒ2+๐œŒ1โˆ’2โ„œ๐”ข[๐‘ค1๐‘ค2ฬ…]โˆ’2=2|๐‘ค1โˆ’๐‘ค2|๐œŒ1๐œŒ2=๐‘˜(๐‘ค1,๐‘ค2)โ–ก
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  2. 2Im done 2ฯ€