Highly precise and maintenance-free bearing technology for slit lamps in ophthalmology

Profile

• What was needed: bar stock that can be processed precisely down to the nearest μm to form bearings
• Manufacturing process: the bar stock was supplied to the customer without any further processing
• Requirements: highest precision, customised bearing shape, bearing for easy and silent running, hygienic use without additional lubricant, long service life
• Material: iglidur® J
• Branch of industry: medical equipment
• Success for the customer: The mechanical processing of the sleeve, especially the cutout for the cables, was very problematic as a brass part. With plastic, we were able to offer the customer a cost-effective solution.

Demanding task: bearing for a microscope arm

The slit lamp is to the ophthalmologist what the drill is to a dentist. The microscope enables close examination of the various areas of the eye with up to 40 times magnification, thus facilitating a holistic diagnosis and the detection of various eye disorders.  Great technical demands are placed on the mechanical design of the medical device. Thomas Herberger, designer at A. R. C., : "One critical issue is the movement of the microscope arm. It must be very easy to move the lamp, high-precision guides are required for the axes – because every irregularity and every unwanted motion is magnified 40-fold to the ophthalmologist through the microscope. Small adjustments in position are vital, however, when the ophthalmologist is searching for haemorrhages on the retina, for example. At the same time, he must be able to securely fix the microscope arm. “

Problem

The slit lamp is to the ophthalmologist what the drill is to a dentist. The microscope enables close examination of the various areas of the eye with up to 40 times magnification, thus facilitating a holistic diagnosis and the detection of various eye disorders. The technical requirements for the mechanical construction of the medical device are high. One critical issue is the movement of the microscope arm. It must be very easy to move the lamp, high-precision guides are required for the axes – because every irregularity and every unwanted motion is magnified 40-fold to the ophthalmologist through the microscope. Small adjustments in position are vital, however, when the ophthalmologist is searching for haemorrhages on the retina, for example. At the same time, he or she must also be able to securely fix the microscope arm.
The slit lamps tested by medical technology manufacturer A.R. C. either prioritised ease of operation or precision. Operating both aspects was all the more difficult to achieve because the microscope is about 250 millimetres away from the bearing of the movable arm, forming a lever that makes precise and clearance-free bearing difficult.
In addition, it was also important that the plain bearing material is homogeneous so that the sliding properties are always the same even with machined components. Another important factor is silent motion and freedom from lubrication: ophthalmologists don't want to have to be greasing their equipment. Last but not least, service life is a central criterion because split lamps are often used all day, every day for decades.

Solution

In their search for the best possible bearing solution, the designers from A.R.C. came across the iglidur plain bearings. These bearings have already proven their worth in other areas of medical technology. When feed movements are performed, bearings with the standard E 10 fit are, as a rule, sufficient. In the case of A.R.C. slit lamp, significantly higher requirements had to be met. Here we are at the limits of what can be produced mechanically. Therefore, in close cooperation with A.R.C. a customised solution was worked out, which ensures the best possible fit with the smallest possible clearance while at the same time providing extremely smooth running and the possibility of fixing the setting. The material pairing was also adapted to this bearing solution.
The plain bearings used are components made of iglidur J - the bearings supplied as bar stock are manufactured in the factory of A.R.C. which involves high precision tooling down to the nearest μm in order to obtain the desired fit. At the design stage, attention was paid to ensuring that the walls of the plastic plain bearings were as thin as possible in order to ensure the highest degree of dimensional stability. One factor that complicated matters was that A.R.C. makes openings in the bearing bushes to allow electrical cables to pass through the slit lamp arms.
A.R.C. also uses the plastic plain bearings at other bearing points of the slit lamp and is very satisfied with them. In combination with the used stainless steel and brass, perfect results are achieved here. The example impressively demonstrates that any reservations about the use of plastic bearings in medical technology are misplaced. On the contrary, these bearings make it possible to achieve the highest level of precision, being able to dispense with lubricants is very beneficial for reasons of hygiene. The intense endurance tests performed by A.R.C. over months also provide evidence of the long service life of the precision bearing on the microscope arm.

It was here that A. R. C., saw even more potential for improvement: "The slit lamps we tested either prioritised ease of operation or precision. But we wanted to offer both. "This was all the more difficult as the microscope is around 250 millimetres from the bearing of the moveable arm, thus forming a lever that makes it trickier to provide a precise and clearance-free bearing. In their search for the best possible bearing solution, the designers from A. came across R. C., igus® plain bearings made of high-performance plastics from the iglidur® range. These bearings have already proven their worth in other areas of medical technology. When feed movements are performed, bearings with the standard E 10 fit are, as a rule, sufficient. In the case of A. R. C. slit lamp, significantly higher requirements had to be met. Thomas Herberger: "Here, we are in a area that tests the limits of what can be produced mechanically. "This is why we worked together with igus® to produce a customised solution that ensures the best possible fit, with the smallest possible clearance while at the same time providing extremely smooth running and the possibility of fixing the setting. The combination of materials was aligned to this bearing solution.