﻿ Pin in a Slot Mechanisms kinematic Chains RP

# Step 2.8: Model 'Pin in a Straight Slot'

### A 'Pin-in-a-Slot' Mechanism

You may think a 'Pin-in-a-Slot joint' is a special joint. It is not the RPR or RPP Dyad.

Note: A Pin-in-a-Slot is generic term we use for a joint where it seems that a Pin-Joint moves along or parallel to a Slide-Joint.

When we design a Pin-in-a-Slot, we often make the joint identically to Diagram 'A'.

Diagram A shows a mechanical configuration.

There are apparently two Parts in diagram A:

 • Part that includes a Roller / Pin-Joint
 • Part that includes a Slot / Slide-Joint

However, it is best to re-imagine the slot configuration as three Parts.

In Diagram B, there are three Parts:

 • Part that includes a Pin
 • Part that includes a Slot
 • Part the Slide-Block - the 'extra' Part.

It is best to imagine Part is a Slide-Rail, and Part is a Slide-Block that slides along the Slide-Rail.

Diagram C shows an equivalent system to Diagram B. Diagram C shows that the Pin-Joint is not always on the axis of the actual Slide-Joint.

There are two examples of the 'Pin-in-Slot' dyad below.

The physical design might be a cam-follower bearing in a straight slot, or a part that pivots on a THK-Slider that itself moves along a THK Rail.

Cam-Follower in a Slot - Geneva Mechanism

THK Slider and Rail - Dwell Mechanism

 General: To model a Pin-in-a-Slot

 STEP 1: Draw a Line† in Part - in this case, it is drawn in the Base-Part

Edit the position of the Line. It will be the 'Slide-Rail'

This Part is the Slide-Block.

 STEP 3: Join Part to Part with a Slide-Joint
 STEP 4: If necessary, add a Point‡ in Part to set the position of the Pin-Joint in Part
 STEP 5: Join Part to the Point in Part with a Pin-Joint

Notes:

You can also use a CAD-Line in Part

You can also use a Point at the one of the CAD-Line in the Part

 Eight Possible Kinematic-Chains with a Pin-in-a-Slot

The Pin-in-a-Slot is actually two of the three Joints that are in a Dyad.

In the Dyads we describe below, the letters R-P represent the two Joints.

 • The R is the Pin-Joint (R is for Revolute-Joint - the kinematic name of a Pin-Joint)
 • The P is the Slide-Joint (P is for Prismatic-Joint - the kinematic name for a Slide-Joint)

When you add a third joint, which may be a Slide-Joint(P) or a Pin-Joint(R), the Dyad is complete.

When you join the Dyad to a Rocker or a Slider, it is possible to build eight different kinematic-chains

 1 RP+R + Rocker or RP+R + Slider. The Dyad is an RPR Dyad.
 2 RP+P + Rocker or RP+P + Slider. The Dyad is an RPP Dyad.
 3 R+RP + Rocker or R+RP + Slider. The Dyad is an RRP Dyad.
 4 P+RP + Rocker or P+RP + Slider (or PR+P + Rocker or PR+P + Slider). The Dyad is a PRP Dyad.

Remember, each Dyad may have up to four different closures. See Change Dyad Closure.

Configuration 1 (See Step 2.7)

This is a Rocker and an R-P-R Dyad

Join Part to the Base-Part with a Pin-Joint

Join Part to Part with a Slide-Joint. The Joint uses the CAD-Line in the two Parts.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Pin-Joint.

[A Motion-Dimension FB identifies the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual rotation of Part]

Configuration 2

This is a Rocker and an R-R-P Dyad (or P-R-R if you prefer to start from the Motion Driven Joint)

Part is joined to the Base-Part with a Pin-Joint

[A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual rotation of Part]

Part is joined to Part with a Slide-Joint. The Joint uses the CAD-Line in the two Parts.

Part is joined to Part with a Pin-Joint .

Part is joined to the Base-Part with a Pin-Joint.

Configuration 3 (See Step 2.6)

This is a Rocker and an R-P-P Dyad

Join Part to the Base-Part with a Slide-Joint

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to Base-Part with a Pin-Joint.

[A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual rotation of Part]

Configuration 4

This is a Slider and an R-R-P Dyad (or a P-R-R if you prefer to start from the Driven Joint)

Join Part to the Base-Part with a Slide-Joint

[A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual displacement of Part]

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Pin-Joint.

Configuration 5

This is a Slider and an P-R-P Dyad

Join Part to the Base-Part with a Slide-Joint

[A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual displacement of Part]

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. The Slide-Joint happens to lie at a fixed angle of approximately 60º

Configuration 6

This is a Rocker and an P-R-P Dyad

Join Part to the Base-Part with a Pin-Joint

[A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual rotation of Part]

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. The Slide-Joint happens to lie at a fixed angle of approximately 60º

Configuration 7

This is a Slider and an R-P-R Dyad

Join Part to the Base-Part with a Pin-Joint

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. The Slide-Joint happens to lie at a fixed angle of approximately 60º

[A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual displacement of Part]

Configuration 8

This is a Slider and an R-P-P Dyad

Join Part to the Base-Part with a Slide-Joint

Add a Line to Part. Use the new Line to join Part to Part with a Slide-Joint.

Join Part to Part with a Pin-Joint

Join Part to the Base-Part with a Slide-Joint. The Slide-Joint happens to lie at a fixed angle of approximately 60º

[A Motion-Dimension FB identifies Part as the Part we will move with a specified motion.

The motion-values at the input-connector to the Motion-Dimension give the actual displacement of Part]

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