Automated Greenhouse Window Vent System Analysis

Introduction

This session focuses on the mechanical analysis of an automated window vent system for the mini greenhouse, focusing on the rack and pinion mechanism. The goal is to understand the forces involved in opening and closing the window.

Design Requirements

The key requirements for the window vent system are:

Window Orientation: The window is required to open to be perpendicular to the greenhouse’s back panel.
Window Mass: The mass of the window is 0.5kg, which will influence the force calculations.
Mechanism Design: The rack must be attached, forming a pin-jointed mechanism, for smooth operation.
Motor Configuration: The basic system design includes two motors, positioned on each side of the mini greenhouse, to drive the window opening mechanism.

Remember to take into account the mass of the rack. This will depend on your design. You could assume it to be 250g initially and adjust it later.

Assumptions:

The assumptions below can be made to simplify the analysis:

The operation is considered frictionless.
Acceleration is not considered; forces will be calculated at equilibrium.
The centre of mass of the window is assumed to be in its center, simplifying the calculations.
A safety factor of 1.2 is applied to the motor force to appropriately size the motor, accounting for the additional force required during acceleration.

Task: Force Analysis

Draw the Free Body Diagram (FBD): Start by sketching the FBD of the window mechanism, identifying all forces acting on the system.
Calculate Forces & moments at Equilibrium: Considering the window’s mass and the requirement for it to open perpendicular to the back panel, calculate the force on the rack when the window is closed and when it is open.

You must define the position of the pinion pivot point, we recommend defining it as x and y coordinates relative to the lid hinge point. You should also define how far along the lid the rack is attached.

Focus on the moments around the hinge to understand how forces balance.

Extension Tasks:

Single Motor Design: Consider how the system’s design would change if it were driven by a single motor using a shaft to distribute the force to both sides of the window. What implications would this have for the motor sizing and the overall mechanics of the system?
Reaction Forces: Reflect on the reaction forces that the fasteners and holding brackets must withstand. How does this affect their design? This consideration is crucial for ensuring the structural integrity of the window mechanism.