Robotically Assisted Manufacturing Workcell

The Vandalbot Senior Design team was tasked with developing prrof of concept for a robotically assisted work cell that could assemble various rivet and nut plate assemblies. The purpose is to create a automated and safe work cell that would free workers from the highly repetitive task of putting these assemblies together. Thorough documentation of the project will be helpful to future students and design teams and provide students with practical experience in industrial automation.

Design Task
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Problem Statement
Hundreds of nut plate assemblies are built every day using human labor. This work is monotonous and physically taxing for the workers involved, often resulting in injury due to repetitive motions. In addition to causing workplace injury, the repetitive nature of these tasks results in an accumulation of process errors. The goal of this project is to create an automated work cell centered on an industrial robot which can tirelessly and consistently perform these assembly tasks which are ill-suited for human workers.

Design Goals

 * Safety
 * Robot enclosure protocols
 * Removing humans from the manufacturing task
 * Providing students with practical experience in industrial automation
 * Creating thorough documentation for future students and design teams
 * Creation of a proof of concept for a process that can be used for production
 * 1st semester goals
 * Understand current assembly process
 * Establish baseline of mock parts
 * Develop a proposal for an automated process using one industrial robot
 * Develop a concept for tooling and part orientation, including prototype tools and fixturing
 * 2nd semester goals
 * Programming of the robotic process
 * Final design and construction of fixturing and tooling required for process
 * Presentation and exit (feeding/removing parts in work cell)
 * As a stretch goal: multiple, collaborative robots (will require additional safety features)

Detailed Specifications
1. Quick and Efficient Process
 * At least as fast as a human operator
 * Robot should be able to operate with minimum human input
 * Robot can be adaptedto various nut plate assembly tasks with minimal setup time

2. Correct Rivet Placement
 * Rivet depth must be withing the tolerance requirements, -0/+0.010 inches
 * Rivets must be placed at a minimum distance of two rivet head diameters away from the edge of the plate and from other rivets

3. Correct Nut Plate Placement
 * The clocking of the nut place is positioned within 2 degrees from the drawing specifications
 * The nut plate is positioned within 0.030 inches from the drawing specifications

4. Minimal Human Interaction
 * Assembly requires at most a worker to place parts into the work cell and remove completed assemblies

Current Manufacturing Process
This is the current manufacturing process for a nut plate assembly as built by a human worker. Note that some assemblies have multiple types of rivets and nut plates.
 * 1) Receive 'shoebox' full of parts
 * 2) Follow specifications on work instruction
 * 3) Gather materials
 * 4) Use a test plate to check Winslow drill depth
 * 5) Drill countersinks and rivet holes with Winslow drill
 * 6) Load rivets and tape down
 * 7) Flip part over and place nut plates into position
 * 8) C-squeeze to fasten rivets
 * 9) Place completed assemblies back into ‘shoebox’

Robotic Cell Improvements/Problem Solving
1. Encoder Error
 * Traced back to dead encoder batteries
 * Replacement batteries were ordered and issue was resolved

2. Calibration
 * Joints J1, J2, J3, and J5 can be calibrated because they have built in mechanical stops
 * Joint J4 requires a CALSET screw in order to set a mechanical stop for calibration
 * Joint J6 requires a CALSET jig to calibrate
 * CALSET screw for J4 located inside J3 access panel
 * Contacted Denso support regarding CALSET jig, which is sold separately from the robot
 * J6 CALSET jig ordered and received
 * Robot fully calibrated and ready for operations

3. Enable Auto Mode Error
 * Error appeared when attempting to switch robot to auto mode in order ro run programs
 * According to the manual, there is a circuit that needs to be shorted in order to enable this mode
 * Robot assembly includes a toggle switch to short this circuit
 * Tested switch with DMM and found it functioning properly
 * Checked fuses in robot controller and found that none were blown
 * Tried a different robot controller and problem continued
 * Checked wiring and found a lose wire, which was soldered back together
 * Robot now able to switch into auto mode and run programs

End of Fall Semester Concept
1. Retrieve part from palletized box
 * Part introduced into the work cell via a palletized box
 * Robot programmed to pick up each part in sequence

2. Winslow drilling operation, vacuum, and deburring
 * Robot positions part at a mounted Winslow drill and vacuum
 * Drilling and countersink operation is performed for all holes
 * Robot moves parts to deburring tool
 * Deburring operation is performed for all holes

3. Rivet and nut plate positioning and squeeze operation
 * Robot positions part horizontally on workstation
 * Rivets fed into holes from below using compressed air
 * Part shifted a short distance where a single nut plate is dropped onto the rivets
 * Part shifted once again where both rivets are squeezed simultaneously

4. Place finished part into receiving box
 * Robot places each part into a receiving box to be removed at the end of the operation