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12/5/2014 | Low friction, self-aligning miniature linear ball bushing bearings improve accuracy of thermal imaging camera

What should a design engineer do when off-the- shelf components do not meet design specifications for a new application while custom components have a reputation as an expensive alternative? Brian Gattman, Sr. Mechanical Engineer at Fluke discovered that a custom linear guide solution for his application could actually save money and improve the accuracy and performance of his design.

Design Challenges

Fluke Corporation, a world leader in compact, professional electronic test and measurement equipment was designing a new thermal imaging camera and encountered design challenges which could not be overcome with standard components on the market.

The Fluke TI400 camera range features the unique LaserSharp™ Auto Focus system that achieves consistently in-focus images essential for accurate infrared inspection. The camera bounces a laser beam off the target, measuring the time of flight to calculate the distance from camera to target. This information is then mapped to the focus mechanism that positions the movable lens to the correct distance from the sensor rapidly and precisely.

The moveable lens is located inside the camera so that the outer lens can be fixed. It’s designed to be supported by and travel on a miniature linear ball bushing bearing. During development it became clear that plain linear bearings with their inherently high friction would not meet the required demanding specification for supporting and adjusting the position of the lens. Brian Gattman, Sr. Mechanical Engineer at Fluke explained: “For use in a compact, light-weight, hand-held instrument we needed an extremely small bearing, just 3mm diameter, but it also had to be very low friction to minimize the power requirement for the focus system which is a significant factor in battery life for the instrument. We found that Thomson “off the shelf” 1/8 inch linear ball bushing bearings performed well but the 3mm bearing size we needed was not available in their standard range. After some discussion, Thomson quickly tooled up to produce a 3mm bearing, which proved to have a consistently low coefficient of friction that allowed us to use a motor of only 300mN force with associated low power consumption and also small size, so helping to reduce the size of the product. Most critically, the exceptionally low static friction (stick/slip effect) gave the smooth operation we needed for fast and accurate focusing.”

A second critical requirement was the temperature range of the bearing. Thermal imaging products must work impeccably in high temperature environments; Fluke specified 50°C ambient. Coupled with up to 25°C rise due to heat dissipation inside the unit, the bearing must perform at up to 75°C. At the other end of the scale, storage temperatures can be as low as -20°C giving an overall range of almost 100°C, a serious challenge for the grease in this assembly. As well as the expected increase in friction at lower temperatures due to thicker grease, tests also revealed that friction varied significantly depending on the amount of grease in the bearing. To arrive at an optimum solution, Fluke engineers tested a number of different lubricants and developed a rig for injecting exactly the right quantity into the bearing housing. For the large numbers of bearings involved, removing and replacing the standard grease was not a realistic option and, Thomson production engineers worked with Fluke to incorporate the special grease in production using a refined version of the Fluke jig.

Benefits of the Custom Solution

A high-precision, low-friction miniature linear ball bushing bearing minimized size and weight, maximized battery life, and focused performance of Fluke’s high performance hand-held TI400 thermal imaging camera. It took a custom, stainless steel and polymer corrosion-resistant compact bearing from Thomson to meet Fluke’s unique requirements. The optimal solution illustrated here is not uncommon for machine design engineers who take time to collaborate closely with their preferred component manufacturers.

“All through the development phase and into pre-production Thomson and Fluke have worked together very effectively and starting late 2013, with the TI400 range now in full production, deliveries have been on target and to specification. Close cooperation between our two organizations has been a major factor in the success of this project”, said Brian Gattman.

Customization by Thomson of the miniature linear ball bushing bearings enabled Fluke to find the optimal linear guidance solution for their thermal imaging camera. The standard Thomson bearings’ small size, low friction and increased accuracy were already attractive to Fluke and it took only minor modification by Thomson to meet Fluke’s precise performance requirements.

About Thomson

With more than 70 years of motion control innovation and quality, Thomson Industries, Inc. is the industry’s premier producer of Linear Ball Bushing ® Bearings and Profile Rail Bearings, 60 Case ® Shafting, ground and Ball and Lead Screws, Linear Actuators, Gearheads, Clutches, Brakes, Linear Systems, and related accessories. Thomson invented the Linear Ball Bushing Bearing in 1945, and has set the standard ever since with an unsurpassed set of mechanical motion control solutions serving global commercial and aerospace & defense markets. Thomson Industries, Inc. has facilities in North America, Europe and Asia with over 2000 distributor locations around the world.

About Fluke LaserSharp™

The Fluke Ti400 infrared camera is equipped with LaserSharp™ AutoFocus for perfectly focused images. Every. Single. Time. Every infrared camera user knows that focus is the single most important thing to ensure when conducting an infrared inspection. Without an in-focus image temperature measurements may not be accurate, sometimes by as much as 20 degrees, so it's much easier to miss a problem. LaserSharp auto focus tells you exactly where you are focusing. It uses a laser to calculate the distance to your target before it focuses. Place the red laser dot on the equipment you are inspecting, then pull and release the trigger for a perfect in-focus image.

Thomson, 1500 Mittel Boulevard, Wood Dale, IL 60191-1073; 1-540- 633-3549; 1-540- 633-0294 (fax); Thomson@thomsonlinear.com; www.thomsonlinear.com.

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