For the joy stick handle, adjustment knob and patient chin rest used in the Computed Anatomy TMS-2 instrument, RESIN SYSTEMS uses a flexible elastomeric urethane resin formulation to yield parts with the right feel and texture to ensure optimal comfort for both the patient and the instrument operator.
Cast Urethane Elastomer Parts Enhance Comfort Factor for Ophthalmologic Instrument Operators and Patients
Computed Anatomy Corporation of New York, NY is an electronic engineering firm that for a decade has been developing and marketing specialized medical diagnostic instrumentation for ophthalmologic and optometric applications. In particular, the company pioneered systems to measure and evaluate corneal topography (i.e., mapping the shape and surface quality of corneas).
Video images captured by the instrument are computer-analyzed and the resultant information is used in a number of ways ranging from diagnosing eye diseases and conditions to custom-fitting contact lenses. Computed Anatomy’s newest offering — the Topographic Modelling System-2 (TMS-2) — is a third-generation instrument that produces a color-coded topographic map of the cornea.
How to Optimize An Instrument’s Interface to Human Operators and Patients
In developing the TMS-2, Computed Anatomy designers were concerned about three components critical to the way in which the operator and patient interface with the instrument. For the patient, this involves a chin rest (used to keep the head steady during the measurement procedure). For the operator, this involves the handle of the joy stick control (used to position the instrument’s measurement apparatus) and the adjustment knob (used to position the patient chin rest).
“Because these three parts routinely contact people, it is important that they have the right feel and texture so they will be comfortable for operator and patient alike,” says Roy Maus, Computed Anatomy’s Vice President of Administration and Manufacturing.
“From the outset, attaining the desired qualities of feel and texture argued against using machined or cast metallic materials, Maus explains. “We considered using injection molded plastic parts, but there were overriding limitations to that approach too. For example, injection molding was very costly for the production quantities we anticipated. Moreover, we had tight time constraints to get the parts into production and tooling up for injection molding is time consuming at best.”
“Even if the cost and time factors were more attractive, attaining the proper feel in the material might have been difficult,” Maus continues. “In addition, the mold parting lines characteristic of injection molding would have been unsightly, meaning we would have had to perform secondary machining to remove them.”
Liquid Resin Casting Produces Parts That Successfully Blend Functionality, Form and Feel
“Utilizing liquid resin cast parts solved these problems for us,” says Maus, “and allowed us to move the parts from design into production in just two months. Tooling up for resin casting was far faster than injection molding (2-4 weeks compared to 8-16 weeks ) and the silicone rubber molds for resin casting were much less expensive than machined metal injection molds (1/10th the cost). Of key importance, this production process yields parts that accurately replicate the finish of the original master parts.”
“For Computed Anatomy’s parts, we formulated a flexible elastomeric urethane material color-coordinated to the TMS-2 instrument,” says RESIN SYSTEMS’ Engineering Manager, Stuart McCord. “This material allows us to produce parts with precisely the right feel and texture (durometer) to ensure optimal comfort for both the patient and the instrument operator. Durability is important too as the parts must withstand repeated handling as well as regular cleansing and sterilization with alcohol wipes.”
“Another advantage of the liquid resin casting process is that it allows us to mold a threaded breass insert directly into the chin rest, and a Delrin shaft into the adjustment knob, saving additional assembly steps. Plus, the total absence of mold parting lines, gate marks and sink marks eliminates the need for secondary machining.” McCord adds, “The finely detailed surface finish was duplicated from a male aluminum master. By contrast, machined plastic and SLA masters don’t adequately develop the surface finish for highly aesthetic parts.”
“We want the human-to-instrument interface of the Computed Anatomy TMS-2 to be as perfect as possible,” concludes Maus, “and RESIN SYSTEMS has enabled us to meet this objective.”