Getting Started Tutorials - MechDesigner > Tutorial 14: Gear-Pairs / Rack-Pinions

Rack-Pinion / Ball-Screw

A Rack is a Linear-Gear. The Rack can drive, or be driven by, a Pinion. The Rack has a linear motion and the Pinion has a angular motion.

The preparation for a Ball-Screw is identical to a Rack and Pinion. Use the Rack-Pinion dialog to enable Rack-Pinion or Ball-Screw.

Add Rack-Pinion removes one(1) degree-of-freedom from a rotating-Part or a sliding-Part.

Terminology

Rack -Pinion :	A Rack-Pinion is a sliding linear-gear (Rack) that is in mesh with a rotating circular-gear (Pinion). The motion of each Part is related by the module and number-of-teeth on the Pinion.
Ball-Screw :	A Ball-Screw is a device in which a Screw rotates to move a Nut, or vice-versa. The Linear-Motion of the Nut and the rotation of the Screw are related by the lead of the screw-thread.
sliding-Part :	a Part that you join to a different Part with a Slide-Joint.
rotating-Part :	a Part that you join to a different Part with a Pin-Joint.

Prepare Add Rack-Pinion

Prepare: Driving Pinion; Driven Rack

MD-GA-RackPinion-Prep-0

Elements before you do Add Rack-Pinion

Line - in a rotating-Part that is kinematically-defined

Line - in a sliding-Part that is not kinematically-defined

Prepare: Driving Rack, Driven Pinion

Elements before you do Add Rack-Pinion

Line - in a sliding-Part that is kinematically-defined

Line - in a rotating-Part that is not kinematically-defined

Add Rack-Pinion

Driving Pinion; Driven Rack

STEP 1: Click Add Rack-Pinion

1.Add menu > Mechanism menu > Add Rack-Pinion

1.Machine-elements toolbar > Add Rack-Pinion

In the Command-Manager, there are two elements to select.

STEP 2: Select the two elements in the graphics-area

1.Click Line - it is in the Part that is kinematically-defined.

2.Click Line - it is in the Part that is NOT kinematically-defined.

STEP 3: Complete the Command

1.Command-Manager: Click to complete Add Rack-Pinion.

Result :

The Pinion is on the Rotating-Part.

The rotating-axis of the Pinion is coincident with the Pin-Joint.

The Rack is on the Sliding-Part.

The Rack is parallel with the Slide-Joint.

The Pitch-Line of the Rack is offset from the center of the Pinion by the Pitch-Circle Radius of the Pinion.

The sliding-Part is now a Part that is kinematically-defined.

Driving Rack; Driven-Pinion

STEP 1:Add Rack-Pinion

1.Add menu > Mechanism menu > Add Rack-Pinion

1.Machine-elements toolbar > Add Rack-Pinion

In the Command-Manager, there are two elements to select.

STEP 2:Select the two elements in the graphics-area

2.Click Line - it is in the Part that is kinematically-defined.

3.Click Line - it is in the Part that is NOT kinematically-defined.

STEP 3:Complete the Command

4.Click in the Command-Manager.

The Rack-Pinion is now in the Assembly-Tree and graphics-area.

Result :

The Pinion is on the Rotating-Part.

The rotating-axis of the Pinion is coincident with the Pin-Joint.

The Rack is on the Sliding-Part.

The Pitch-Line of the Rack is parallel to the Slide-Joint and sliding-Part.

The rotating-Part is now a Part that is kinematically-defined.

Kinematics-Tree of Rack-Pinion

MD-ADD-RACKPINION-KINEMATICS-TREE

When the movement of the Pinion comes from the Rack

Before you do Add Rack-Pinion, there is a sliding-Part that is kinematically-defined and a rotating-Part that has one degree-of-freedom.

After you do Add Rack-Pinion, the sliding-Part(Rack) and the rotating-Part (Pinion) are kinematically-defined.

When the movement of the Rack comes from the Pinion

Before you do Add Rack-Pinion, the rotating-Part is kinematically-defined and the sliding-Part has one degree-of-freedom.

After you do Add Rack-Pinion, the rotating-Part (Pinion) and sliding-Part (Rack) are kinematically-defined, and in one kinematic-chain.

Rack and Pinion / Ball-Screws