Robotic Arm IV Insertion
Abstract
Peripheral Intravenous Cannulation, the process of inserting a small catheter into the bloodstream, is the most common clinical routine practiced in the US. With a failure rate of 35% to 50% and over 2.7 million operations daily, the use for an automated solution is critical.
As a Duke Pratt Fellow, I work under Dr.Oca's lab to design a mechanical end effector for a UR5E robot arm. Starting from scratch, I am responsible for the end-to-end design, fabrication, and controls for the end effector. The goal is to use an ultrasonic sensor to scan the length of the arm, detect the appropriate vein, and use the end effector to insert the IV catheter with a closed-loop control system.
Goals
- Design a reliable mechanical end effector for IV insertion.
- Develop inverse kinematics to control motors for precise movement.
- Use closed-loop control feedback from both motor encoders and ultrasound to target a vein.
Targets
- Reduce weight for non-critical components.
- Create an accurate 3D mold with different vein densities for testing.
- Preform accuracy tests to determine IV insertion error.
Project Features
Initial Designs
In order for the needle to reach a specific point directly underneath the ultrasound, a 4-bar linkage was design to offsett the rotation axis of the needle to below the ultrasound. From there, 2 linear actuators were designed to both push the needle in and hold the catheter in place as the needle retracted. In order to design these components three subassemblies were made: linear actuator catheter insertion, 4-bar linkage, and the UR5E base.
Subassembly: IV Insertion
The pair of linear actuators act as both the puncture device and the syringe. These two motors work together to both insert and remove the IV, accounting for the distance from the skin and the depth of the injection.
Subassembly: 4-Bar Linkage
The four-bar system works to minimize the needle's movement after it punctures the skin. Most straight pieces are cut out of steel using a Trotec waterjet and 3D-printed pieces were designed to be easily printed on any printer. Springs were later added as a counterweight measure to reduce the torque required to move the 4-bar system.
Subassembly: UR5E Base
The base consists of the attachment to the UR5 robot arm as well as a casing that surrounds the ultrasonic sensor needed for scanning the arm. Here, a motor rotates the four-bar mechanism changing the angle at which the IV is injected. A gear reduction is used to increase the torque and thus the rigidity of the entire structure.
Rapid Prototyping
With the initial cad completed last semester, prototyping and assembly of the end effector was completed this semester. Assembled from both 3D-printed parts and waterjet aluminum, the end effector was successfully able to move.
Flange added to prevent the bearings from falling out. Optimized design to decrease weight while maintaining structural rigidity.
New side mount created to account for bearings and Nema 17 motor. Shortened base to reduce torsion along the length of the device and to reduce wobble.
Extra holes added to secure aluminum bars better. New converging 4-bar reduced print time for connecting pieces while avoiding collision with the ultrasound in the center of the device.
Fabrication
Assembly
- Place IV insertion end effector relative to the dedicated vein by using the 4-bar subassembly.
- Changes angle of the needle to 45 degrees relative to arm using the 4-bar subassembly.
- Slightly extend the large actuator to move the needle closer to the arm.
- Decrease the angle by 5 to 10 degrees using the 4-bar subassembly
- Extend small actuator in the needle subassembly to place catheter into the vein
- Retract long actuator in the needle subassembly to pull needle out
- Retract small actuator in the
needle subassembly once catheter has been placed.
- Return mechanism to home position by changing the position using the 4-bar subassembly.
