﻿ 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 design the construction we see in Diagram A.

Diagram A shows one possible mechanical configuration.

There are apparently two Parts in diagram A:

 • Part : the lever with a pin roller at its end
 • Part : the part with a linear slot

While there are apparently two parts, it is best to re-imagine the Pin-in-a-Slot configuration as three Parts.

Diagram B shows a different mechanical configuration, but with three Parts:

 • Part : the lever, with a pin-joint at its end
 • Part : the part with a slot
 • Part : the 'block'  that slides along the slot [Slide-Joint], AND and is also joined to the lever [Pin-Joint]  - this is the 'extra' Part.

We can imagine Part as a Slide-Rail, and Part as a Sliding-Block that slides along the Slide-Rail, similar to a THK Slide-Rail and Sliding-Block

Diagram C shows a system that is equivalent kinematically to Diagram B.

Diagram C shows that the Pin-Joint is not always on the axis of the 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

Add dimensions and constraints to the Line. It will be the 'Slide-Rail'.

 STEP 3: Join Part to Part with a Slide-Joint

Part is now the 'Slide-Block'.

 STEP 4: If necessary, edit Part to add a Point‡ 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 add a CAD-Line in a Part or use the CAD-Line along the centre of the Part.

STEP 4 may not be necessary as you can use the start-Point or end-Point CAD-Line in Part when you do STEP 5.

### 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 rotation to the 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 rotation to the 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 rotation to the 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 displacement to the 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 displacement to the 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. This Slide-Joint is 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 rotation to the 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 is at 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 is 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 displacement to the 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 is 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 displacement to the Part]

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