MechDesigner Reference & User Interface > 2.2 Mechanism-Editor > Mechanisms > Machine elements > Rack-Pinion

Rack-Pinion / Ball-Screw

Terminology

Rack -Pinion :	A Rack-Pinion is the term for a sliding, straight, linear-gear (Rack) that is in mesh with a rotating, circular, gear-wheel (Pinion). The motions of the two Parts are kinematically 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 is joined to another Part with a Slide-Joint.
rotating-Part :	A Part that is joined to another Part with a Pin-Joint.

How to prepare for Add Rack-Pinion (typical)

There are two model types.

A: The motion of the Rack is from the motion of a Pinion:

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

Line or CAD-Line

B: The motion of the Pinion is from the motion of a Rack

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

Line or CAD-Line

Add Rack-Pinion

A: If the motion of the Rack is from the motion of a Pinion

STEP 1: Click Add Rack-Pinion

1.Mechanism menu > 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 in the Part that is kinematically-defined.

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

STEP 3: Complete the Command

1.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.

MD-17-CM-AddRackPinion-01

B: If the motion of the Pinion is from the motion of a Rack

STEP 1:Add Rack-Pinion

1.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

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.

MD-17-CM-AddRackPinion-01-A

Kinematics-Tree of Rack-Pinion

MD-ADD-RACKPINION-KINEMATICS-TREE

If the motion of the Pinion is from the motion of 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.

If the motion of the Rack is from the motion of the Pinion

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

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

Rack-Pinion - Ball-Screw