By Tobias Munch
Product Line Specialist Screws and Screw Jacks
The use of lead screws with guide rails is a well-accepted technology for applications requiring linear motion in all types of industries. This traditional solution is, however, over-engineered for many smaller applications where only light duty is required. In areas such as lab automation and 3D printing the need for a smaller footprint, reliable operation and low maintenance from a much easier to install, simpler solution has a great deal of appeal to machine builders. Understanding this requirement, linear motion expert, Thomson, has developed a new product known as the ‘Glide Screw’, which combines linear bearing and lead screw into a single device without the need for additional guidance components.
The new patent pending Thomson Glide Screw has a much smaller footprint than the traditional round or profile rail screw and guide systems. It is quicker and easier to install, removes alignment issues and is effectively maintenance-free. Its innovative design provides fast, smooth and quiet operation in an integrated, reliable, high performing linear motion solution.
Innovative design
Traditional linear motion systems, which use a screw and guide, do not make use of the outside diameter of the screw. To create a better solution for smaller footprint applications, Thomson has eliminated the need for external guides by using the outside of the screw as a bearing surface. The resulting product takes just a lead screw and lead nut to produce a simple and elegant linear motion solution that has real benefit in small machines.
A traditional lead screw and lead nut can handle an axial load which transitions through the nut threads to contact bearings at the bottom and top of the system. This system cannot, however, take side or moment loads. Such loading would cause all sorts of problems, including binding, squeaking, higher torque and premature failure of the device. To resolve this, the Thomson screw has a bearing grade finish with radial bearings, which slide along the outside of the screw. The bearing carriage is between the inside races of the radial bearings and outside diameter of the screw. To handle radial loads, opposing reactionary forces are created where the bearings hit the outside of the screw. Twisting or moment loads also transition through the bearings in the opposing direction. In this way, the simple lead screw and lead nut design of the Glide Screw can handle axial, radial and moment loads in the system.
With no external guides, the Glide Screw has a much smaller footprint than alternate technologies and the simplified design has fewer parts. Compared with an equivalent traditional round rail system, for example, the Glide Screw has less than 40% of the components. Systems that use linear guides also require careful alignment of the screw with the guides and careful preparation of reference surfaces. Any misalignment of such devices will create failures in testing or premature failure in the field. The design of the Thomson Glide Screw is such that the product is pre-aligned at the factory and minimal time is required to install and align when it is applied within a machine. All that is needed along with the Glide Screw itself is a feature to stop rotation.
The Glide Screw is manufactured from bearing grade plastic and stainless steel materials and is designed for effectively maintenance-free use. It incorporates the proven Thomson “Lube-4- Life” technology as standard within the product. This self-lubricating system uses a polymer block contained within the lead nut. The block is a sponge, which has lubricant inside its pores, and, as the nut moves along the screw, a small amount of lubricant diffuses out, keeping the system sufficiently lubricated to maintain long-term performance and reliability.
Ideal for use in wide range of small machines
The Glide Screw offers the ideal solution in many laboratory medical applications where a smaller, cleaner, smoother and quieter linear motion system has real benefits, such as syringe and fluid pumps. It also offers a fast and precise solution, which is more cost-effective than traditional linear guided systems, which are over-designed for use in areas such as fluid pipetting, or lab automation machines where movement is required in three axes. In the rapidly growing area of 3D printing, the Glide Screw can decrease complexity and improve machine reliability while offering time and cost savings in manufacturing.
Thomson stock a range of standard metric and imperial standard sizes with flanged and cylindrical nut bodies for rapid delivery. Optional configurations are available for use in high temperature applications (such as ovens or autoclaves), clean room environments and processes requiring food grade materials. Depending upon machine requirements, the screws can be mounted with fixed/fixed, fixed/supported or supported/supported end supports. An efficient customisation service is also available from Thomson for custom nut configurations, screw diameters and thread leads to match exact customer specifications beyond the standard range of products.
Fast Installation and Reliable Operation
Since the Glide Screw is both the drive system and linear guide, the device is already perfectly aligned and cannot bind. It can handle axial, moment or side loads without additional linear guidance or support and its use assures long-term high performance and reliability and enables more compact machine design.
Overall the simplified design and pre-alignment of the Glide Screw means it takes much less time to install into a machine. Compared with a round rail guided linear motion system, installation, surface preparation and alignment takes typically less than 25% of the time. Compared with a profile rail, which demands great care and needs tight tolerances in surface preparation, the use of the Guide Screw requires no reference surfaces and can take just 15% of the time required to install. Along with the Lube-4- Life lubrication block removing the need for any regular maintenance, the total cost of ownership is dramatically reduced compared with many alternate technologies.
Summary
The integrated lead screw and linear bearing provided by the Glide Screw offers a breakthrough solution to linear motion requirements in small machines. It removes the need to use traditional designs, which are over-engineered and over-complicated for the duty required. Its compact size can reduce a machine’s footprint or allow for additional functionality to be added within given space constraints. It does not require careful component alignment for good operation, reducing machine assembly time, lowering production costs and improving overall reliability. Its elegant yet simple design provides fast, smooth, quiet operation without the need for ongoing lubrication maintenance.
Thomson designed the Glide Screw with an understanding of the needs and demands of small machine builders. With standard and custom sizes available, this device offers an innovative alternative to complex, traditional linear motion solutions for many applications including small-scale laboratory automation, medical imaging, multi-axis printing and pick and place machines. Where light duty linear motion is required, it can lower the total cost of ownership of a machine and deliver overall improved performance.