The combination of rotary drive and axial vibration required the use of high-quality plain bearings not only to implement freedom of movement in the axial direction, but also to achieve the most accurate signals possible at high vibration frequencies.
To make the repair process safer, in a project called the Smart Drill, a student group from Bremen Institute of Measurement Technology, Automation and Quality Science (BIMAQ) developed an attachment for the existing drilling machine. During the drilling process, it measures the depth of the hole in order to determine the correct screw. Due to the special demands on the bearing points of the measuring system, such as resistance to chemicals and moisture, as well as a trouble-free mounting at high speeds, the use of plastic self-lubricating bearings was explored.
The special requirements of the medical drilling machine were to develop an optimal bearing in different speed and vibration frequency ranges without a negative influence on the system. “The combination of rotary drive and axial vibration requires the use of high-quality plain bearings not only to implement freedom of movement in the axial direction, but also to achieve the most accurate signals possible at high vibration frequencies,” explained Michael Sorg of BIMAQ. To cover all requirements, various igus plain bearings were compared with iglidur L500 selected as the best option.
The chosen plain bearing has low friction values and high wear resistance and allows both the rotary and the axial movement. It is also far from its load limit so can easily accommodate drill speeds of up to 900rpm.
In addition, the bearing withstands medical sterilisation at extreme temperatures. Moisture resistance also plays an important role – iglidur L500 absorbs a negligible amount of water. The lack of lubrication eliminates the risk of contamination of the wound or a premature bearing failure due to washout of the lubricant. Thus, the bearing meets medical hygiene requirements.
The low installation sizes and light weight compared to metallic bearings were also decisive factors.
