Types of Mechanical Liaisons: Pivot and Sliding

This page explores two specific types of mechanical liaisons: the pivot and the sliding liaison.

Pivot Liaison (X-axis)

The pivot liaison allows rotation around a single axis, typically the X-axis in this example.

• Contacts: 1 point contact, 1 cylindrical surface contact
• Degrees of freedom: 1 $rotation around X-axis$
• Translations: $0, 0, 0$
• Rotations: $1, 0, 0$

Example: A door handle connected to a door demonstrates a pivot liaison.

Sliding Liaison (X-axis)

The sliding liaison permits linear movement along a single axis, in this case, the X-axis.

• Contacts: 1 straight line contact, 1 planar surface contact
• Degrees of freedom: 1 $translation along X-axis$
• Translations: $1, 0, 0$
• Rotations: $0, 0, 0$

Example: A drawer sliding in and out of a dresser illustrates a sliding liaison.

Both liaisons are represented with specific symbols in 2D and 3D diagrams, helping engineers and designers quickly identify the type of mechanical connection in a system.

Vocabulary: Degré de liberté mécanique $Mechanical degree of freedom$ refers to the independent movements a body can make in three-dimensional space.

This page provides a clear comparison between two fundamental types of mechanical liaisons, highlighting their differences in allowed movements and practical applications.

Advanced Mechanical Liaisons: Sliding Pivot and Ball Joint with Finger

This section delves into more complex mechanical liaisons: the sliding pivot and the ball joint with finger.

Sliding Pivot Liaison (X-axis)

The sliding pivot liaison combines rotational and translational movement along the same axis.

• Contacts: 1 cylindrical surface contact
• Degrees of freedom: 2 $rotation and translation along X-axis$
• Translations: $1, 0, 0$
• Rotations: $1, 0, 0$

Example: The connection between a piston and the body of a cylinder in an engine demonstrates a sliding pivot liaison.

Ball Joint with Finger Liaison (Z-axis drive)

This liaison allows rotation around two axes while restricting movement along the third axis.

• Contacts: 1 spherical surface contact
• Degrees of freedom: 2 $rotations around X and Y axes$
• Translations: $0, 0, 0$
• Rotations: $1, 1, 0$

Highlight: The ball joint with finger liaison is crucial in many mechanical systems where controlled multi-axis rotation is required.

Both liaisons are represented with specific symbols in 2D and 3D diagrams, providing a visual shorthand for engineers and designers.

Vocabulary: Liaison mécanique degré de liberté $Mechanical liaison degree of freedom$ describes the specific movements allowed by a particular type of mechanical connection.

This page expands on the concept of mechanical liaisons, introducing more complex types that allow for multiple degrees of freedom. Understanding these liaisons is essential for designing and analyzing more sophisticated mechanical systems.

Spherical and Planar Support Liaisons

This page introduces two important types of mechanical liaisons: the spherical liaison $ball joint$ and the planar support liaison.

Spherical Liaison (Ball Joint)

The spherical liaison, centered at point A, allows rotation around all three axes.

• Contacts: 1 spherical surface contact
• Degrees of freedom: 3 $rotations around X, Y, and Z axes$
• Translations: $0, 0, 0$
• Rotations: $1, 1, 1$

Example: The connection between a joystick and a game controller often uses a spherical liaison.

Planar Support Liaison (Normal to Y-axis)

The planar support liaison permits movement along a plane and rotation around its normal axis.

• Contacts: 1 planar surface contact
• Degrees of freedom: 3 $translations along X and Z axes, rotation around Y-axis$
• Translations: $1, 0, 1$
• Rotations: $0, 1, 0$

Example: A sheet of paper resting on a table demonstrates a planar support liaison.

Both liaisons are represented with specific symbols in 2D and 3D diagrams, aiding in quick identification and understanding of mechanical systems.

Vocabulary: Liaison pivot $Pivot liaison$ is a type of mechanical connection that allows rotation around a single axis, similar to how a door hinge operates.

This page expands on the variety of mechanical liaisons, introducing types that allow for multiple degrees of freedom in different configurations. Understanding these liaisons is crucial for analyzing and designing complex mechanical systems where multi-directional movement is required.

Linear Annular and Linear Rectilinear Liaisons

This section explores two types of linear liaisons: the linear annular liaison and the linear rectilinear liaison.

Linear Annular Liaison (X-axis)

The linear annular liaison allows rotation around its axis and translation along two perpendicular axes.

• Contacts: 1 circular line contact
• Degrees of freedom: 4 $rotation around X-axis, translations along Y and Z axes$
• Translations: $0, 1, 1$
• Rotations: $1, 0, 0$

Example: The connection between a tennis ball and the tube of a ball launcher illustrates a linear annular liaison.

Linear Rectilinear Liaison (X-axis, normal to Y-axis)

This liaison permits translation along its axis and rotations around two perpendicular axes.

• Contacts: 1 straight line contact
• Degrees of freedom: 4 $translation along X-axis, rotations around Y and Z axes$
• Translations: $1, 0, 0$
• Rotations: $0, 1, 1$

Example: The interaction between an ice skate blade and the ice surface demonstrates a linear rectilinear liaison.

Both liaisons are represented with specific symbols in 2D and 3D diagrams, providing a visual shorthand for engineers and designers.

Vocabulary: Types de liaisons mécaniques $Types of mechanical liaisons$ refer to the various ways mechanical parts can be connected, each allowing specific movements and restricting others.

This page introduces more specialized types of mechanical liaisons, highlighting their unique properties and applications. Understanding these liaisons is essential for designing and analyzing complex mechanical systems that require specific types of linear movement combined with rotational freedom.

Point Contact and Helical Liaisons

This section examines two unique types of mechanical liaisons: the point contact liaison and the helical liaison.

Point Contact Liaison (Normal to Y-axis)

The point contact liaison allows movement in all directions except along its normal axis.

• Contacts: 1 point contact
• Degrees of freedom: 5 $translations along X and Z axes, rotations around all axes$
• Translations: $1, 0, 1$
• Rotations: $1, 1, 1$

Example: The tip of a pencil touching a sheet of paper demonstrates a point contact liaison.

Helical Liaison (X-axis)

The helical liaison combines rotation and translation along the same axis in a fixed ratio.

• Contacts: 1 point contact, 1 cylindrical surface contact
• Degrees of freedom: 1 $but with 2 conjugate movements$
• Translations: $1, 0, 0$
• Rotations: $1, 0, 0$

Example: The connection between a screw and a nut illustrates a helical liaison.

Both liaisons are represented with specific symbols in 2D and 3D diagrams, aiding in quick identification and understanding of mechanical systems.

Vocabulary: Degré de liberté mécanique formule $Mechanical degree of freedom formula$ refers to the mathematical expression used to calculate the number of independent movements possible in a mechanical system.

This page introduces two specialized types of mechanical liaisons with unique properties. The point contact liaison offers extensive freedom of movement, while the helical liaison demonstrates how rotation and translation can be coupled in a single degree of freedom. Understanding these liaisons is crucial for designing and analyzing complex mechanical systems that require specific types of movement or constraints.

Fixed Joint Liaison

This final section focuses on the fixed joint liaison, also known as an encastrement.

Fixed Joint Liaison

The fixed joint liaison completely restricts all movement between the connected parts.

• Contacts: 1 point contact, 1 cylindrical surface contact, 1 planar surface contact
• Degrees of freedom: 0 $no movement allowed$
• Translations: $0, 0, 0$
• Rotations: $0, 0, 0$

Example: The connection between a beam and a wall in a building structure demonstrates a fixed joint liaison.

The fixed joint liaison is represented with a specific symbol in both 2D and 3D diagrams, indicating complete restriction of movement.

Vocabulary: Liaison mécanique Animation $Mechanical liaison animation$ refers to visual representations or simulations that demonstrate how different types of mechanical liaisons function and move.

This page concludes the exploration of mechanical liaisons by presenting the most restrictive type. The fixed joint liaison is crucial in engineering and construction where stability and immobility are required. Understanding this liaison, along with all the previously discussed types, provides a comprehensive view of how mechanical parts can be connected and constrained in various systems.

Highlight: The study of mechanical liaisons is fundamental to engineering design, allowing for the creation of complex machines and structures by understanding how different parts can be connected and how their movements can be controlled or allowed.

Understanding Mechanical Liaisons

This page introduces the fundamental concepts of mechanical liaisons and contacts between parts.

A mechanical liaison occurs when there is at least one contact between two parts. The guide identifies three types of contacts:

1. Point contact $e.g., sphere on a plane$
2. Line contact $e.g., cylinder on a plane$
3. Surface contact $e.g., plane on plane, cylinder in cylinder$

Definition: A mechanical liaison is the connection between two parts that have at least one point of contact.

The concept of degrees of freedom is introduced to characterize the possible movements between two parts. To accurately describe these movements, a local reference frame is associated with the contact. This frame must be orthonormal and direct, with at least one vector aligned with an axis of symmetry or normal to a tangent plane of contact.

Highlight: In the local reference frame, a given liaison can have up to 6 degrees of freedom: 3 rotations $Rx, Ry, Rz$ and 3 translations $Tx, Ty, Tz$.

This introduction sets the foundation for understanding more complex mechanical liaisons and their applications in engineering and design.