Glaukos Automated Hypodermic Tube Washing Fixture

Project Overview

Glaukos, a leader in glaucoma treatment devices, challenged our team to automate the labor-intensive hypodermic tube cleaning process used in their ocular stent injection products. This process requires precision cleaning of 21-32 gauge stainless steel tubes using multiple ultrasonic baths and ID washing steps, traditionally performed manually.

We developed an automated system using an Epson C4 6-axis robotic arm, custom mechanical fixtures, and sensor-based feedback to automate bulk handling, individualization, and washing of hypodermic tubes, improving throughput and consistency while reducing labor requirements.

My Role: Robotics Integration and System Coordination

I focused on integrating subsystems with the Epson C4 robot to execute the automated wash process:

Programmed the Epson RC+ software to move tubes through the cleaning workflow using sensor triggers and timing logic.
Coordinated subsystem interface requirements for seamless tube handoff between bulk washing, individualization, and ID washing.
Collaborated with mechanical and electrical leads to ensure the robot’s end effector design, layout, and sensor system aligned with the automated workflow.

Project Requirements:

Automated Workflow: Transfers tubes through ultrasonic baths and ID washing stations without human intervention.
Bulk to Individual Tube Handling: Custom-designed “individualizer” funnels and catch trays to separate and present single tubes for robotic pickup.
Precision Sensing: Waterproof PNP photoelectric sensors signal the robot when a tube is ready for transfer.
Compact Layout: Designed to operate within a 30” x 60” fume hood workspace, enabling lab integration.

Technical Highlights:

Robotics: Epson C4 6-axis robot programmed to handle delicate 0.5mm diameter tubes while maintaining positioning accuracy within tight workspace constraints
Individualizer Subsystem: Utilized vibration motors and pulsed water jets to agitate tubes through a ribbed funnel, overcoming surface tension challenges for single-tube presentation
Sensor Integration: Selected and tested IP67-rated PNP sensors to detect tube presence underwater reliably
Simulation-Driven Design: Performed FEA on tube gripping forces, leading to the addition of silicone padding on the end effector to prevent tube deformation
System Testing: Validated tube throughput (goal: ≥120 tubes/hr), with sensors and robot control achieving reliable single-tube transfers during testing

Finite Element Analysis: Ensuring Safe Tube Handling

Why FEA Was Needed

The hypodermic tubes (0.5 mm diameter, 21-32 gauge stainless steel) used in Glaukos products are fragile and precision-critical. During robotic handling, excessive gripping force from the end effector could cause plastic deformation, leading to blockages or failures in clinical use.

To design a reliable, automated gripping system, we needed to determine:

The maximum allowable gripping force without damaging the tubes.
Whether design modifications (e.g., adding soft pads) would protect the tubes while ensuring secure gripping during robotic transfer.

FEA Simulation Setup:

We performed a 2D static structural simulation using SolidWorks Simulation to analyze the tube under gripping conditions:

Geometry: Simplified cross-section of the tube placed between two flat plates, representing the steel gripper fingers.
Material Properties: Tube- Stainless steel with a yield strength of 25 ksi (≈172 MPa).
Loading: Incrementally applied normal compressive forces on the plates, simulating the gripping force from the end effector.
Boundary Conditions: Plates fixed in position with force applied perpendicular to the tube surface.

Setup of FEA of Tube with Steel End Effector Fingers

Stress Plot of Stresses on Tube

FEA of Tube with Silicon Buffer Pads

Key Findings:

Without Padding:

At a gripping force of 15 lbf (≈67 N), the tube yielded, with von Mises stresses exceeding 25 ksi at the contact points.
Safe gripping force determined to be 0.5 lbf (≈2.2 N) to avoid permanent deformation, which is too low for reliable handling under wet conditions.

With Silicone Buffer Pads:

Added 1/8 inch silicone rubber padding between the gripper and tube.
Simulation showed that the compliant interface distributed the contact pressure, reducing stress concentration at contact points.
Allowed gripping forces up to 30 lbf (≈133 N) without exceeding the tube’s yield stress.
Enabled the robot to reliably grip the tube in wet and dry conditions without damage.