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    39-245

    Rapid Design through Virtual and Physical Prototyping

    Carnegie Mellon University

    dxWrapDistLeft0dxWrapDistRight0wzTooltipposrelv3dhgt251661312fLayoutInCell1fAllowOvment0fIsButton1fHidden0fLayoutInCell1

    Introduction to MechanismsYi Zhang

    with

    Susan Finger

    Stephannie BehrensTable of Contents

    4 Basic Kinematics of Constrained Rigid Bodies

    4.1 Degrees of Freedom of a Rigid Body

    4.1.1 Degrees of Freedom of a Rigid Body in a Plane

    The degrees of freedom (DOF) of a rigid body is defined as the number of independent movements it has

    rigid body in a plane. To determine the DOF of this body we must consider how many distinct ways the b

    two dimensional plane such as this computer screen, there are 3 DOF. The bar can be translatedalong ththey axis, and rotatedabout its centroid.

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    Figure 4-1 Degrees of freedom of a rigid body in a plane

    4.1.2 Degrees of Freedom of a Rigid Body in Space

    An unrestrained rigid body in space has six degrees of freedom: three translating motions along thex,y a

    rotary motions around thex,y andzaxes respectively.

    Figure 4-2 Degrees of freedom of a rigid body in space

    4.2 Kinematic Constraints

    Two or more rigid bodies in space are collectively called a rigid body system. We can hinder the motion

    rigid bodies with kinematic constraints.Kinematic constraints are constraints between rigid bodies that r

    the degrees of freedom of rigid body system.

    The term kinematic pairs actually refers to kinematic constraints between rigid bodies. The kinematic pa

    pairs and higher pairs, depending on how the two bodies are in contact.

    4.2.1 Lower Pairs in Planar Mechanisms

    There are two kinds of lower pairs in planar mechanisms: revolute pairs andprismatic pairs.

    A rigid body in a plane has only three independent motions -- two translational and one rotary -- so introd

    pair or a prismatic pair between two rigid bodies removes two degrees of freedom.

    Figure 4-3 A planar revolute pair (R-pair)

    Figure 4-4 A planar prismatic pair (P-pair)

    4.2.2 Lower Pairs in Spatial Mechanisms

    There are six kinds of lower pairs under the category ofspatial mechanisms. The types are: spherical pair

    pair, revolute pair,prismatic pair, and screw pair.

    Figure 4-5 A spherical pair (S-pair)

    Aspherical pairkeeps two spherical centers together. Two rigid bodies connected by this constraint will

    relatively aroundx,y andzaxes, but there will be no relative translation along any of these axes. Thereforemoves three degrees of freedom in spatial mechanism. DOF = 3.

    Figure 4-6 A planar pair (E-pair)

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    Aplane pairkeeps the surfaces of two rigid bodies together. To visualize this, imagine a book lying on a

    in any direction except off the table. Two rigid bodies connected by this kind of pair will have two indepmotions in the plane, and a rotary motion around the axis that is perpendicular to the plane. Therefore, a p

    degrees of freedom in spatial mechanism. In our example, the book would not be able to raise off the tab

    table. DOF = 3.

    Figure 4-7 A cylindrical pair (C-pair)

    A cylindrical pairkeeps two axes of two rigid bodies aligned. Two rigid bodies that are part of this kind

    independent translational motion along the axis and a relative rotary motion around the axis. Therefore, a

    removes four degrees of freedom from spatial mechanism. DOF = 2.

    Figure 4-8 A revolute pair (R-pair)

    A revolute pairkeeps the axes of two rigid bodies together. Two rigid bodies constrained by a revolute protary motion around their common axis. Therefore, a revolute pair removes five degrees of freedom in s

    = 1.

    Figure 4-9 A prismatic pair (P-pair)

    Aprismatic pairkeeps two axes of two rigid bodies align and allow no relative rotation. Two rigid bodiekind of constraint will be able to have an independent translational motion along the axis. Therefore, a pr

    five degrees of freedom in spatial mechanism. DOF = 1.

    Figure 4-10 A screw pair (H-pair)

    Thescrew pairkeeps two axes of two rigid bodies aligned and allows a relative screw motion. Two rigid

    screw pair a motion which is a composition of a translational motion along the axis and a corresponding

    axis. Therefore, a screw pair removes five degrees of freedom in spatial mechanism.

    4.3 Constrained Rigid Bodies

    Rigid bodies and kinematic constraints are the basic components of mechanisms. A constrained rigid bod

    kinematic chain, a mechanism, a structure, or none of these. The influence of kinematic constraints in the

    has two intrinsic aspects, which are the geometrical and physical aspects. In other words, we can analyzeconstrained rigid bodies from their geometrical relationships or usingNewton's Second Law.

    A mechanism is a constrained rigid body system in which one of the bodies is the frame. The degrees of

    when considering a constrained rigid body system that is a mechanism. It is less crucial when the system

    does not have definite motion.

    Calculating the degrees of freedom of a rigid body system is straight forward. Any unconstrained rigid bo

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    freedom in space and three degrees of freedom in a plane. Adding kinematic constraints between rigid bo

    correspondingly decrease the degrees of freedom of the rigid body system. We will discuss more on this tmechanisms in the next section.

    4.4 Degrees of Freedom of Planar Mechanisms

    4.4.1 Gruebler's Equation

    The definition of the degrees of freedom of a mechanism is the number of independent relative motions a

    For example, Figure 4-11 shows several cases of a rigid body constrained by different kinds of pairs.

    Figure 4-11 Rigid bodies constrained by different kinds of planar pairs

    In Figure 4-11a, a rigid body is constrained by a revolute pairwhich allows only rotational movement aro

    degree of freedom, turning around point A. The two lost degrees of freedom are translational movementsThe only way the rigid body can move is to rotate about the fixed point A.

    In Figure 4-11b, a rigid body is constrained by aprismatic pairwhich allows only translational motion. Inone degree of freedom, translating along thex axis. In this example, the body has lost the ability to rotate

    cannot move along they axis.

    In Figure 4-11c, a rigid body is constrained by a higher pair. It has two degrees of freedom: translating al

    and turning about the instantaneous contact point.

    In general, a rigid body in a plane has three degrees of freedom. Kinematic pairs are constraints on rigid bdegrees of freedom of a mechanism. Figure 4-11 shows the three kinds of pairs inplanar mechanisms. Th

    number of the degrees of freedom. If we create alower pair(Figure 4-11a,b), the degrees of freedom are

    if we create a higher pair(Figure 4-11c), the degrees of freedom are reduced to 1.

    Figure 4-12 Kinematic Pairs in Planar Mechanisms

    Therefore, we can write the following equation:

    (4-1)

    Where

    F = total degrees of freedom in the mechanism

    n = number oflinks(including the frame)l = number oflower pairs (one degree of freedom)

    h = number ofhigher pairs (two degrees of freedom)

    This equation is also known as Gruebler's equation.

    Example 1

    Look at the transom above the door in Figure 4-13a. The opening and closing mechanism is shown in Fig

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    calculate its degree of freedom.

    Figure 4-13 Transom mechanism

    n = 4 (link 1,3,3 and frame 4), l = 4 (at A, B, C, D), h = 0

    (4-2)

    Note: D and E function as a same prismatic pair, so they only count as one lower pair.

    Example 2

    Calculate the degrees of freedom of the mechanisms shown in Figure 4-14b. Figure 4-14a is an applicatio

    Figure 4-14 Dump truck

    n = 4, l = 4 (at A, B, C, D), h = 0

    (4-3)

    Example 3

    Calculate the degrees of freedom of the mechanisms shown in Figure 4-15.

    Figure 4-15 Degrees of freedom calculation

    For the mechanism in Figure 4-15a

    n = 6, l = 7, h = 0

    (4-4)

    For the mechanism in Figure 4-15b

    n = 4, l = 3, h = 2

    (4-5)

    Note: The rotation of the roller does not influence the relationship of the input and output motion of the m

    freedom of the roller will not be considered; It is called apassive orredundantdegree of freedom. Imagi

    welded to link 2 when counting the degrees of freedom for the mechanism.

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    4.4.2 Kutzbach Criterion

    The number ofdegrees of freedom of a mechanism is also called the mobility of the device. The mobility

    parameters (usually pair variables) that must be independently controlled to bring the device into a particKutzbach criterion, which is similar to Gruebler's equation, calculates the mobility.

    In order to control a mechanism, the number of independent input motions must equal the number of deg

    mechanism. For example, the transom in Figure 4-13a has a single degree of freedom, so it needs one ind

    to open or close the window. That is, you just push or pull rod 3 to operate the window.

    To see another example, the mechanism inFigure 4-15a also has 1 degree of freedom. If an independent

    (e.g., a motor is mounted on joint A to drive link 1), the mechanism will have the a prescribed motion.

    4.5 Finite Transformation

    Finite transformation is used to describe the motion of a point on rigid body and the motion of the rigid b

    4.5.1 Finite Planar Rotational Transformation

    Figure 4-16 Point on a planar rigid body rotated through an angle

    Suppose that a pointPon a rigid body goes through a rotation describing a circular path fromP1

    toP2

    aro

    coordinate system. We can describe this motion with a rotation operatorR12

    :

    (4-6)

    where

    (4-7)

    4.5.2 Finite Planar Translational Transformation

    Figure 4-17 Point on a planar rigid body translated through a distance

    Suppose that a pointPon a rigid body goes through a translation describing a straight path fromP1

    toP2

    coordinates of (

    x, y). We can describe this motion with a translation operatorT12:

    (4-8)

    where

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    (4-9)

    4.5.3 Concatenation of Finite Planar Displacements

    Figure 4-18 Concatenation of finite planar displacements in spaceSuppose that a pointPon a rigid body goes through a rotation describing a circular path fromP

    1toP

    2'ar

    coordinate system, then a translation describing a straight path fromP2'toP

    2. We can represent these two

    (4-10)

    and

    (4-11)

    We can concatenate these motions to get

    (4-12)

    where D12

    is theplanar general displacement operator:

    (4-13)

    4.5.4 Planar Rigid-Body Transformation

    We have discussed various transformations to describe the displacements of a point on rigid body. Can thto the displacements of a system of points such as a rigid body?

    We used a 3 x 1 homogeneous column matrix to describe a vector representing a single point. A benefici

    x 3 translational, rotational, and general displacement matrix operators is that they can easily be programmanipulate a 3 x n matrix of n column vectors representing n points of a rigid body. Since the distance of

    body from every other point of the rigid body is constant, the vectors locating each point of a rigid body m

    transformation when the rigid body moves and the proper axis, angle, and/or translation is specified to re(Sandor & Erdman 84). For example, the general planar transformation for the three pointsA, B, Con a r

    represented by

    (4-14)

    4.5.5 Spatial Rotational Transformation

    We can describe a spatial rotation operator for the rotational transformation of a point about an unit axis

    origin of the coordinate system. Suppose the rotational angle of the point about u is , the rotation op

    by

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    (4-15)

    where

    ux, u

    y, u

    zare the othographical projection of the unit axis u onx,y, andzaxes, respectively.

    s

    = sin

    c

    = cos

    v

    = 1 - cos

    4.5.6 Spatial Translational Transformation

    Suppose that a pointPon a rigid body goes through a translation describing a straight path fromP1

    toP2

    coordinates of (

    x, y, z), we can describe this motion with a translation operatorT:

    (4-16)

    4.5.7 Spatial Translation and Rotation Matrix for Axis Through the Origin

    Suppose a pointPon a rigid body rotates with an angular displacement about an unit axis u passing throu

    coordinate system at first, and then followed by a translationDu along u. This composition of this rotatiothis translational transformation is a screw motion. Its corresponding matrix operator, thescrew operator

    the translation operator in Equation 4-7 and the rotation operator in Equation 4-9.

    (4-17)

    4.6 Transformation Matrix Between Rigid Bodies

    4.6.1 Transformation Matrix Between two Arbitray Rigid Bodies

    For a system of rigid bodies, we can establish a local Cartesian coordinate system for each rigid body. Tr

    are used to describe the relative motion between rigid bodies.

    For example, two rigid bodies in a space each have local coordinate systems x1y

    1z

    1and x

    2y

    2z

    2. Let pointP

    at location (x2, y

    2, z

    2) in body 2's local coordinate system. To find the location ofPwith respect to body 1

    system, we know that that the point x2y

    2z

    2can be obtained from x

    1y

    1z

    1by combining translationL

    x1along

    z about z axis. We can derive the transformation matrix as follows:

    (4-18)

    If rigid body 1 is fixed as a frame, a global coordinate system can be created on this body. Therefore, the

    can be used to map the local coordinates of a point into the global coordinates.

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    4.6.2 Kinematic Constraints Between Two Rigid Bodies

    The transformation matrix above is a specific example for two unconstrained rigid bodies. The transform

    the relative position of the two rigid bodies. If we connect two rigid bodies with akinematic constraint, th

    will be decreased. In other words, their relative motion will be specified in some extent.

    Suppose we constrain the two rigid bodies above with a revolute pairas shown in Figure 4-19. We can st

    transformation matrix in the same form asEquation 4-18.

    Figure 4-19 Relative position of points on constrained bodies

    The difference is that theLx1

    is a constant now, because the revolute pair fixes the origin of coordinate sy

    to coordinate system x1y

    1z

    1. However, the rotation z is still a variable. Therefore, kinematic constrai

    transformation matrix to some extent.

    4.6.3 Denavit-Hartenberg Notation

    Denavit-Hartenberg notation (Denavit & Hartenberg 55) is widely used in the transformation of coordina

    and robot mechanisms. It can be used to represent the transformation matrix between links as shown in th

    Figure 4-20 Denavit-Hartenberg Notation

    In this figure,

    zi-1

    and ziare the axes of two revolute pairs;

    iis the included angle of axes x

    i-1and x

    i;

    diis the distance between the origin of the coordinate system x

    i-1y

    i-1z

    i-1and the foot of the common

    aiis the distance between two feet of the common perpendicular;

    iis the included angle of axes z

    i-1and z

    i;

    The transformation matrix will be T(i-1)i

    (4-19)

    The above transformation matrix can be denoted as T(ai,

    i,

    i, d

    i) for convenience.

    4.6.4 Application of Transformation Matrices to Linkages

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    A linkage is composed of several constrained rigid bodies. Like a mechanism, a linkage should have a fra

    can be used to derive the kinematic equations of the linkage. If all the links form a closed loop, the concatransformation matrices will be an identity matrix. If the mechanism has n links, we will have:

    T12

    T23

    ...T(n-1)n

    = I

    Table of Contents

    Complete Table of Contents

    1Introduction to Mechanisms

    2Mechanisms and Simple Machines

    3More on Machines and Mechanisms4Basic Kinematics of Constrained Rigid Bodies

    4.1Degrees of Freedom of a Rigid Body

    4.1.1Degrees of Freedom of a Rigid Body in a Plane4.1.2Degrees of Freedom of a Rigid Body in Space

    4.2Kinematic Constraints

    4.2.1Lower Pairs in Planar Mechanisms4.2.2Lower Pairs in Spatial Mechanisms

    4.3Constrained Rigid Bodies

    4.4Degrees of Freedom of Planar Mechanisms4.4.1Gruebler's Equation

    4.2.24.4.2 Kutzbach Criterion

    4.5 4.5Finite Transformation

    4.5.1Finite Planar Rotational Transformation

    4.5.2Finite Planar Translational Transformation4.5.3Concatenation of Finite Planar Displacements

    4.5.4Planar Rigid-Body Transformation4.5.5Spatial Rotational Transformation

    4.5.6Spatial Translational Transformation

    4.5.7Spatial Translation and Rotation Matrix for Axis Through the Origin4.6Transformation Matrix Between Rigid Bodies

    4.6.1Transformation Matrix Between two Arbitray Rigid Bodies

    4.6.2Kinematic Constraints Between Two Rigid Bodies

    4.6.3Denavit-Hartenberg Notation4.6.4Application of Transformation Matrices to Linkages

    5Planar Linkages6Cams7Gears

    8Other Mechanisms

    IndexReferences

    0100090000032a0200000200a20100000000a201000026060f003a03574d46430100000000000100ebf900

    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    http://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#topmailto:[email protected]:[email protected]:[email protected]://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#topmailto:[email protected]:[email protected]
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    30000000000

    [email protected]

    (4-9)4.5.3 Concatenation of Finite Planar Displacements

    Figure 4-18 Concatenation of finite planar displacements in space

    Suppose that a pointPon a rigid body goes through a rotation describing a circular path fromP1

    toP2'ar

    coordinate system, then a translation describing a straight path fromP2'toP

    2. We can represent these two

    (4-10)

    and

    (4-11)

    We can concatenate these motions to get

    mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.cs.cmu.edu/~sfinger/home.htmlhttp://www.cs.cmu.edu/~sfinger/home.htmlmailto:[email protected]:[email protected]://www.cs.cmu.edu/~sfinger/home.html
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    (4-12)

    where D12

    is theplanar general displacement operator:

    (4-13)

    4.5.4 Planar Rigid-Body Transformation

    We have discussed various transformations to describe the displacements of a point on rigid body. Can th

    to the displacements of a system of points such as a rigid body?

    We used a 3 x 1 homogeneous column matrix to describe a vector representing a single point. A benefici

    x 3 translational, rotational, and general displacement matrix operators is that they can easily be program

    manipulate a 3 x n matrix of n column vectors representing n points of a rigid body. Since the distance ofbody from every other point of the rigid body is constant, the vectors locating each point of a rigid body m

    transformation when the rigid body moves and the proper axis, angle, and/or translation is specified to re(Sandor & Erdman 84). For example, the general planar transformation for the three pointsA, B, Con a rrepresented by

    (4-14)

    4.5.5 Spatial Rotational Transformation

    We can describe a spatial rotation operator for the rotational transformation of a point about an unit axis

    origin of the coordinate system. Suppose the rotational angle of the point about u is , the rotation op

    by

    (4-15)

    where

    ux, u

    y, u

    zare the othographical projection of the unit axis u onx,y, andzaxes, respectively.

    s

    = sin

    c

    = cos

    v

    = 1 - cos

    4.5.6 Spatial Translational Transformation

    Suppose that a pointPon a rigid body goes through a translation describing a straight path fromP1

    toP2

    coordinates of (

    x, y, z), we can describe this motion with a translation operatorT:

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    (4-16)

    4.5.7 Spatial Translation and Rotation Matrix for Axis Through the Origin

    Suppose a pointP

    on a rigid body rotates with an angular displacement about an unit axis u passing throucoordinate system at first, and then followed by a translationDu along u. This composition of this rotatio

    this translational transformation is a screw motion. Its corresponding matrix operator, thescrew operator

    the translation operator in Equation 4-7 and the rotation operator in Equation 4-9.

    (4-17)

    4.6 Transformation Matrix Between Rigid Bodies

    4.6.1 Transformation Matrix Between two Arbitray Rigid Bodies

    For a system of rigid bodies, we can establish a local Cartesian coordinate system for each rigid body. Trare used to describe the relative motion between rigid bodies.

    For example, two rigid bodies in a space each have local coordinate systems x1y

    1z

    1and x

    2y

    2z

    2. Let pointP

    at location (x2, y

    2, z

    2) in body 2's local coordinate system. To find the location ofPwith respect to body 1

    system, we know that that the point x2y

    2z

    2can be obtained from x

    1y

    1z

    1by combining translationL

    x1along

    z about z axis. We can derive the transformation matrix as follows:

    (4-18)

    If rigid body 1 is fixed as a frame, a global coordinate system can be created on this body. Therefore, thecan be used to map the local coordinates of a point into the global coordinates.

    4.6.2 Kinematic Constraints Between Two Rigid Bodies

    The transformation matrix above is a specific example for two unconstrained rigid bodies. The transform

    the relative position of the two rigid bodies. If we connect two rigid bodies with akinematic constraint, th

    will be decreased. In other words, their relative motion will be specified in some extent.

    Suppose we constrain the two rigid bodies above with a revolute pairas shown in Figure 4-19. We can st

    transformation matrix in the same form asEquation 4-18.

    Figure 4-19 Relative position of points on constrained bodies

    The difference is that theLx1

    is a constant now, because the revolute pair fixes the origin of coordinate sy

    to coordinate system x1y

    1z

    1. However, the rotation z is still a variable. Therefore, kinematic constrai

    transformation matrix to some extent.

    http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#rotationhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#translationhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt3.html#HDR47http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt3.html#HDR47http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR53Ahttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR53Ahttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR53Ehttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#transmatrixhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#transmatrixhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#rotationhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#translationhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt3.html#HDR47http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR53Ahttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR53Ehttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#transmatrix
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    4.6.3 Denavit-Hartenberg Notation

    Denavit-Hartenberg notation (Denavit & Hartenberg 55) is widely used in the transformation of coordina

    and robot mechanisms. It can be used to represent the transformation matrix between links as shown in th

    Figure 4-20 Denavit-Hartenberg Notation

    In this figure,

    zi-1

    and ziare the axes of two revolute pairs;

    iis the included angle of axes x

    i-1and x

    i;

    diis the distance between the origin of the coordinate system x

    i-1y

    i-1z

    i-1and the foot of the common

    ai is the distance between two feet of the common perpendicular;

    iis the included angle of axes z

    i-1and z

    i;

    The transformation matrix will be T(i-1)i

    (4-19)

    The above transformation matrix can be denoted as T(ai

    ,i

    ,i

    , di

    ) for convenience.

    4.6.4 Application of Transformation Matrices to Linkages

    A linkage is composed of several constrained rigid bodies. Like a mechanism, a linkage should have a fracan be used to derive the kinematic equations of the linkage. If all the links form a closed loop, the conca

    transformation matrices will be an identity matrix. If the mechanism has n links, we will have:

    T12

    T23

    ...T(n-1)n

    = I

    Table of Contents

    Complete Table of Contents

    1Introduction to Mechanisms

    2Mechanisms and Simple Machines3More on Machines and Mechanisms

    4Basic Kinematics of Constrained Rigid Bodies

    4.1Degrees of Freedom of a Rigid Body

    http://www.cs.cmu.edu/~rapidproto/mechanisms/references.html#denavit-55http://www.cs.cmu.edu/~rapidproto/mechanisms/tablecontents.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt1.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt1.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt2.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt2.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt3.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt3.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR52http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR52http://www.cs.cmu.edu/~rapidproto/mechanisms/references.html#denavit-55http://www.cs.cmu.edu/~rapidproto/mechanisms/tablecontents.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt1.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt2.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt3.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR52
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    4.1.1Degrees of Freedom of a Rigid Body in a Plane

    4.1.2Degrees of Freedom of a Rigid Body in Space

    4.2Kinematic Constraints4.2.1Lower Pairs in Planar Mechanisms

    4.2.2Lower Pairs in Spatial Mechanisms

    4.3Constrained Rigid Bodies4.4Degrees of Freedom of Planar Mechanisms

    4.4.1Gruebler's Equation

    4.2.24.4.2 Kutzbach Criterion4.5 4.5Finite Transformation

    4.5.1Finite Planar Rotational Transformation

    4.5.2Finite Planar Translational Transformation4.5.3Concatenation of Finite Planar Displacements

    4.5.4Planar Rigid-Body Transformation

    4.5.5Spatial Rotational Transformation

    4.5.6Spatial Translational Transformation

    4.5.7Spatial Translation and Rotation Matrix for Axis Through the Origin4.6Transformation Matrix Between Rigid Bodies

    4.6.1Transformation Matrix Between two Arbitray Rigid Bodies4.6.2Kinematic Constraints Between Two Rigid Bodies

    4.6.3Denavit-Hartenberg Notation

    4.6.4Application of Transformation Matrices to Linkages5Planar Linkages

    6Cams

    7Gears

    8Other MechanismsIndex

    References

    0100090000032a0200000200a20100000000a201000026060f003a03574d46430100000000000100ebf9000000000000018030000010000006c00000000000000000000001a000000370000000000000000000000d2

    d4600000100180300001200000002000000000000000000000000000000f6090000e40c0000d800000017

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    0000c00000001000000250000000c00000001000000180000000c00000000000002540000005400000000

    000370000000100000088870741d1450741000000002c000000010000004c0000000400000000000000000005000000020001a001b00000046000000280000001c0000004744494302000000ffffffffffffffff2a01000

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    00000010000000140000000400000003010800050000000b0200000000050000000c0250005000040000

    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1Chttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR61Dhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR61Ehttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR61Fhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR61Ghttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#4.6.1http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR61Hhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR61Ihttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#HDR61Jhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt5.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt6.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt7.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/mech.chpt8.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/references.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.html
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    40000002d010000040000002d01000004000000020101001c000000fb02f4ff00000000000090010000000726900000000000000000000000000000000000000000000000000040000002d010100040000002d0101

    50000000902000000020d000000320a0c00000001000400000000005100500020000700040000002d0100

    30000000000

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    000d2ffffff000000000000000000000000900100000000000004400022430061006c00690062007200690

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    http://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#topmailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/index.htmlhttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#tophttp://www.cs.cmu.edu/~rapidproto/mechanisms/chpt4.html#topmailto:[email protected]:[email protected]
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    726900000000000000000000000000000000000000000000000000040000002d010100040000002d0101

    50000000902000000020d000000320a0c00000001000400000000005100500020000700040000002d010030000000000

    [email protected]

    39-245

    Rapid Design through Virtual and Physical Prototypi

    Carnegie Mellon University

    We can describe a spatial rotation operator for the rotational transformation of a point about an unit axis upassing through the origin of the coordinate system. Suppose the rotational angle of the point about u is ,the rotation operator will be expressed by

    (4-15)

    where

    ux, uy, uz are the othographical projection of the unit axis u on x, y, and z axes, respectively.s = sinc = cosv = 1 - cos

    4.5.6 Spatial Translational Transformation

    Suppose that a point P on a rigid body goes through a translation describing a straight path from P1 to P2with a change of coordinates of (x, y, z), we can describe this motion with a translation operator T:

    (4-16)

    4.5.7 Spatial Translation and Rotation Matrix for Axis Through the Origin

    Suppose a point P on a rigid body rotates with an angular displacement about an unit axis u passingthrough the origin of the coordinate system at first, and then followed by a translation Du along u. Thiscomposition of this rotational transformation and this translational transformation is a screw motion. Itscorresponding matrix operator, the screw operator, is a concatenation of the translation operator in

    mailto:[email protected]:[email protected]:[email protected]://www.cs.cmu.edu/~sfinger/home.htmlhttp://www.cs.cmu.edu/~sfinger/home.htmlhttp://www.cs.cmu.edu/~rapidproto/home.htmlhttp://www.cmu.edu/mailto:[email protected]:[email protected]://www.cs.cmu.edu/~sfinger/home.htmlhttp://www.cs.cmu.edu/~rapidproto/home.htmlhttp://www.cmu.edu/
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    Equation 4-7 and the rotation operator in Equation 4-9.

    (4-17)

    4.6 Transformation Matrix Between Rigid Bodies4.6.1 Transformation Matrix Between two Arbitray Rigid Bodies

    For a system of rigid bodies, we can establish a local Cartesian coordinate system for each rigid body.Transformation matrices are used to describe the relative motion between rigid bodies.

    For example, two rigid bodies in a space each have local coordinate systems x1y1z1 and x2y2z2. Letpoint P be attached to body 2 at location (x2, y2, z2) in body 2's local coordinate system. To find thelocation of P with respect to body 1's local coordinate system, we know that that the point x2y2z2 can beobtained from x1y1z1 by combining translation Lx1 along the x axis and rotation z about z axis. We canderive the transformation matrix as follows:

    (4-18)

    If rigid body 1 is fixed as a frame, a global coordinate system can be created on this body. Therefore, theabove transformation can be used to map the local coordinates of a point into the global coordinates.

    4.6.2 Kinematic Constraints Between Two Rigid Bodies

    The transformation matrix above is a specific example for two unconstrained rigid bodies. Thetransformation matrix depends on the relative position of the two rigid bodies. If we connect two rigidbodies with a kinematic constraint, their degrees of freedom will be decreased. In other words, theirrelative motion will be specified in some extent.

    Suppose we constrain the two rigid bodies above with a revolute pair as shown in Figure 4-19. We canstill write the transformation matrix in the same form as Equation 4-18.

    Figure 4-19 Relative position of points on constrained bodies

    The difference is that the Lx1 is a constant now, because the revolute pair fixes the origin of coordinate

    system x2y2z2 with respect to coordinate system x1y1z1. However, the rotation z is still a variable.Therefore, kinematic constraints specify the transformation matrix to some extent.

    4.6.3 Denavit-Hartenberg Notation

    Denavit-Hartenberg notation (Denavit & Hartenberg 55) is widely used in the transformation of coordinatesystems of linkages and robot mechanisms. It can be used to represent the transformation matrixbetween links as shown in the Figure 4-20.Figure 4-20 Denavit-Hartenberg Notation

    In this figure,

    * zi-1 and zi are the axes of two revolute pairs;

    * i is the included angle of axes xi-1 and xi;* di is the distance between the origin of the coordinate system xi-1yi-1zi-1 and the foot of the commonperpendicular;

    * ai is the distance between two feet of the common perpendicular;* i is the included angle of axes zi-1 and zi;

    The transformation matrix will be T(i-1)i

    (4-19)

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    The above transformation matrix can be denoted as T(ai, i, i, di) for convenience.

    4.6.4 Application of Transformation Matrices to Linkages

    A linkage is composed of several constrained rigid bodies. Like a mechanism, a linkage should have aframe. The matrix method can be used to derive the kinematic equations of the linkage. If all the linksform a closed loop, the concatenation of all of the transformation matrices will be an identity matrix. If themechanism has n links, we will have:

    T12T23...T(n-1)n = I

    (4-20)

    Table of ContentsComplete Table of Contents

    1 Introduction to Mechanisms2 Mechanisms and Simple Machines3 More on Machines and Mechanisms4 Basic Kinematics of Constrained Rigid Bodies

    4.1 Degrees of Freedom of a Rigid Body

    4.1.1Degrees of Freedom of a Rigid Body in a Plane4.1.2 Degrees of Freedom of a Rigid Body in Space

    4.2 Kinematic Constraints

    4.2.1 Lower Pairs in Planar Mechanisms4.2.2 Lower Pairs in Spatial Mechanisms

    4.3 Constrained Rigid Bodies4.4 Degrees of Freedom of Planar Mechanisms

    4.4.1 Gruebler's Equation4.2.2 4.4.2 Kutzbach Criterion

    4.5 4.5 Finite Transformation

    4.5.1 Finite Planar Rotational Transformation4.5.2 Finite Planar Translational Transformation4.5.3 Concatenation of Finite Planar Displacements4.5.4 Planar Rigid-Body Transformation4.5.5 Spatial Rotational Transformation4.5.6 Spatial Translational Transformation4.5.7 Spatial Translation and Rotation Matrix for Axis Through the Origin

    4.6 Transformation Matrix Between Rigid Bodies

    4.6.1 Transformation Matrix Between two Arbitray Rigid Bodies4.6.2 Kinematic Constraints Between Two Rigid Bodies4.6.3 Denavit-Hartenberg Notation4.6.4 Application of Transformation Matrices to Linkages

    5 Planar Linkages6 Cams

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    7 Gears8 Other MechanismsIndexReferences

    [email protected]