By Eric Anderson
It can be challenging to design and build an automated machine to assemble medical devices that use extruded medical tubing. Extruded tubing can have a mind of its own and the degree of randomness that can be difficult to handle in an automated machine. However, by taking a creative and problem-solving approach, it can still be automated into a successful, reliable process.
Recently, the experts at Steven Douglas Corp. (SDC) completed an automated robotic machine that produces assemblies containing extruded medical tubing. The machine used three, 6-axis Fanuc robots to automatically assemble a medical device that consisted of tubing, a tube clamp and two medical “ports” that were glued to each end of the tubing. In designing the system, SDC’s extensive processing, material handling and automation experience was combined with the customer’s manufacturing knowledge to create a successful automated cell. Key components of this system included the tube feeding and preparation, error proofing and robotic tube handling.
Tube Feeding and Preparation
Before assembly can begin, the medical tubing must be fed into the machine and prepared for the robotic operations that follow. This includes feeding the tube into the system, cutting the tube for the correct length, and installing a clamp on the tube.
When the tubing is fed into the machine consistently, every subsequent step becomes significantly easier and more reliable. However, achieving this is easier said than done. Extruded tubing can have a mind of its own and will act differently depending on many different variables. Limiting these variables is an important aspect in the SDC tube feeding system.
The medical tubing feeding system designed by SDC is simple to operate and maintain without sacrificing any functionality. The tube is fed into the SDC machine from a coil and loaded onto a custom dereeler by an operator. Then, the tube is dispensed through a weighted tension device that separates the tubing from the spool and measures and tracks the amount of tubing that is dispensed and the tension at which it is dispensed. Consistent tension is important. A pair of servo driven belts are used to grab the tube and gently guide it into the machine, which minimizes external effects on the fed tube length.
To complete the system, SDC added in a closed loop control system and machine learning that automatically adjusts the servo in-feed system to ensure the tube length fed is consistent. The SDC feeding system is customizable and adjustable to accommodate a variety of tubing lengths and the integrated error proofing of the machine can easily detect tubing that does not meet the system requirements.
In every application, it’s important for the final products to meet all of our customer, quality and production standards. The medical device industry is no exception. The requirements of most medical devices are more stringent than other industries due to their intended use. An important step in the design of this automated machine is understanding the possible causes of defects and designing a machine to limit these. Considering not evert part will be perfect nor acceptable, process checks can be added to detect and separate the “failed” parts and stop/pause the assembly process as necessary.
Some basic examples, but typically overlooked causes of part defects include running the wrong part or partially assembling a part. To prevent assembling an incorrect part, specific tooling is required to handle each part and sensors are used to ensure the correct tooling is installed. The software, recovery and setup cycles are programmed so that the robots automatically clear the machine of any part that “failed” mid-cycle. This ensures any uncompleted parts are separated from the completed parts.
The same machine vision system that’s used for a vision guided robot can also be used for incoming inspection, as well. For this project, a vision guided robot was used to pick parts off of a conveyor and the vision inspection system verified the correct part was present. An additional vision system was included to inspect the tubing prior to assembly and verify the length of the tubing was correct. Finally, several sensors were added to detect part presence using a series of fiberoptic lasers and capacitive sensors. Another sensor was also installed to verify glue is applied prior to assembly.
By using a combination of all these tools and technologies, SDC was able to design and build a machine that met the required quality standards on 99.9% of the parts. The machine vision system ensured that the .1% of parts that did not meet the required standards were automatically separated.
Robotic Tube Handling
With extruded medical tubing, there is a degree of randomness that can be difficult to handle in an automated machine, especially when the length of the tubing increases. Maintaining control is an important aspect of the SDC machine concept and design. SDC used three individual, 6-axis Fanuc robots that provided flexibility when transitioning between different parts and process steps while still allowing the machine to have full control over the middle and both ends of the tubing at all times.
In this example, once the tubing is fed into the machine, it’s held in a custom trough until one robot grabs one end of the tube and a second robot grabs the other end. Then, each robot moves through a programmed sequence to complete the assembly process of dipping the tubing into glue and then accurately inserting them into the ports on each end. For longer tubing lengths, a custom holder was designed to keep the long loop of the tubing controlled and out of the way for the robots to move through their sequence. Once assembled, a third robot gathers the completed assembly and deposits it into a collection system.
By using multiple robots, the tubing is always controlled, eliminating the possibility of tangling and helping maintain a fast machine cycle time. The robots are also beneficial because they can move in a precisely controlled and monitored way, perfecting the assembly process.
For this process, installing the hose into the fittings was a challenging process that required precision as well as flexibility due to the randomness of the hose. With multiple robots, SDC was able to ultimately setup a very consistent and reliable automated process out of a variable assembly. As a preferred robotic integrator for Fanuc, Epson and many other robot manufacturers, SDC has extensive experience programming multiple robots to work simultaneously, safely and effectively within the same system
Experts in Automated Robotic Systems
SDC is a problem-solving company. Our creative, problem-solving approach and team of experienced automation professionals bring expert knowledge in machine design, mechanical engineering, machine control, robotics programming, parts manufacturing and complete machine assembly. Regardless of whether your application uses extruded medical tubing or if you’re in the medical device industry, the same principles will be applied in the creation of your automated system. We have extensive experience across a broad spectrum of industries, with proven and proprietary methods to build reliable, long-lasting automated machines for a wide variety of applications.
Tags: Assembly & Processing, Joining Technologies, Machine Vision, Material Handling, Medical Devices, Robotic Integration