Pro-Dex Inc., Irvine, CA, is a developer and manufacturer of powered rotary drive surgical and dental instruments. The company’s newest design is a cutting-edge, powered screwdriver that features sensors integrated with software to provide intelligence to the user. Currently in the prototype phase and expected to be commercially available later this year, this specialty screwdriver is being designed for use in highly sensitive surgical procedures.

Exacting Applications in the OR

Fig. 1 – For harsh neurosurgery environments, intelligent screwdrivers assist in making that part of the process smoother.
The operating room needs to be a sterile environment—and, many times, it is an aggressive environment as well. Since the new screwdriver will be used in the OR, it is important that the screwdrivers have a high level of reliability and, like all of the company’s instruments, are ISO certified and FDA compliant. (See Figure 1)

Precision is critical, as the screwdriver will be used for neurosurgery, amongst other types of procedures, on brain tumors or brain trauma caused by accidents. In these operations, a piece of the skull, often of an irregular shape, is usually removed. When the surgery is performed, the skull piece is reattached using a metal plate sometimes held by 15 or more screws.

Thorough Engineering and QC Process

Stuart Gallant, Vice President of Product and Business Development for Pro-Dex, works closely with the company’s material suppliers and a number of groups within the company that are dedicated to ensuring product requirements are met by its suppliers, including reliability engineering, inspection services, and quality control. Performance requirements are considered throughout the prototyping, design, design verification and validation processes, and the supplier is presented with any challenges they need to overcome.

“After evaluating several suppliers, we chose Trelleborg Sealing Solutions because we knew that they were a good and proven supplier of seals, especially for tough environments,” says Gallant. “Most of the projects that we are involved with today, which includes new and existing business, require quality and longevity of sealing solutions.”

Both companies worked together to develop the best screwdriver design possible, using R&D expertise from decades of experience.

Tim Miller, Technical Manager at Trelleborg Sealing Solutions assisted Pro-Dex with their specification process. He explained: “We designed a seal that has a metal body that presses into the bore. This creates the static outer diameter (OD) seal for the part. What is nice about this design is that it doesn’t need any retention or features that hold it in place.”

Form Fits Function

Fig. 2 – PTFE is inherently compatible with most chemicals, providing a long sealing life.
The unique press-fit design of the seal means it locks into the OD to maintain a static seal. The element is a high-grade composition of polytetrafluoroethylene (PTFE)-based resin compound with anti-wear additives. This material is crimped inside the metal body, which is the portion that is press fitted into the bore, creating the static seal. This establishes a lip that will run on the shaft itself. As the shaft rotates, this lip sits and rides on top of it, delivering a very low co-efficient of friction. (See Figure 2)

The screwdriver utilizes a slant coil spring that has a special property to maintain a relatively constant load as it is deflected. As the seal wears or changes dimension due to thermal changes, the force generated by that spring is constant. That consistent force helps ensure that the product has a long life and consistent heat generation.

Meeting Rigorous Requirements

Careful evaluation of all of the components for the screwdriver design revealed that seals can often pose complex and serious challenges. A comprehensive quality control process and a complete physical inspection of the seals ensured that there was no moisture intrusion and leakage. The seals developed specifically for the device have done exceptionally well in a wide array of testing, inspection, and quality control scenarios.

By leveraging shoulder-to-shoulder engineering design and decades of seal expertise, Pro-Dex felt comfortable that they had the right seal for their applications.

Meeting Specific Seal Requirements

Fig. 3 – Custom seals can be developed for just the right precision end use.
“The size of the seals that Trelleborg helped design was a characteristic that was very important to us because we had minimal space for the seal,” says Gallant. “We relied on experts to help us to choose the right seal for the limited space,” which ruled out the potential of using a flanged seal design. (See Figure 3)

“We also wanted to extend the hours of operation and life of our instrument and ensure the seal would hold up. In addition, we were looking to ensure that our powered screwdriver would reduce the amount of time it would take the surgeon to feed the screws into the plate and found that the placing of 15 or even 20 screws into the plate can be achieved in minutes,” said Gallant.