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Why pre-engineered linear motion systems are a smart choice
06 October 2014
Increasingly, machine builders are incorporating pre-engineered linear motion systems into their machines to ensure performance and to reduce cost, risk and time to market compared with building bespoke systems from individual parts, says Anders Trygg, product manager, Thomson Linear Components Group
Specific solutions are easily created using the wide range of proven components now available within these ‘standard’ systems without needing to compromise on specification. Easy to use web-based tools cover mounting orientation, loading conditions, move profile and environmental conditions to speed up the design process for each application and the resulting solution has guaranteed performance and rapid delivery.
A linear motion system typically includes a drive to move a payload, a guide system which handles the load and takes care of any moments, sealing to protect the inner parts of the system and lubrication, such as grease or oil. Selecting the right technology to meet specific requirements is complex and, frequently, a custom built solution seems the only way forward. However, this carries risks in design time and cost to meet the many engineering challenges in ensuring alignment, support, precision and correct sealing of the system.
Linear motion system designer, Thomson, believes there are significant advantages to be gained by selecting pre-engineered solutions to reduce this design time and risk. Thomson is able to provide correctly supported systems which offer easy installation, assured alignment and advanced sealing technology to meet even the harshest environmental conditions. Machine builders can save time and money as well as speed up development cycles by specifying a complete solution supplied fully designed, tested and working to specification for the required operating lifetime.
Modern pre-engineered linear motion systems offer a huge range of options including long stroke lengths (up to 12m), the capability to manage heavy loads and very precise, repeatable movement. Highly effective sealing strategies ensure reliable operation with minimum dust or dirt ingress in applications such as woodworking and painting and in hygienic environments that require regular wash down and cleaning Rapid motor mounting systems enable the use of wide range of interface dimensions. To help machine builders select the optimum motion system from this huge range of options, Thomson's on-line Linear Motioneering design tools are fast and easy to use. Application data are quickly entered via a graphical user interface and the system generates a 3D CAD model of each unique, specified system.
Thomson offers a wide range of electro-mechanical linear motion technologies including ball screw, lead screw and belt drive with choices of guide arrangements, each with different benefits and attributes. Ball screws offer high thrust and good accuracy; lead screws low noise, high accuracy and high repeatability (but are typically not used in high duty cycle applications), and belt drives high speed and high throughput capability.
The guide technology used to carry the payload needs to support top, side and moment loads and the different designs have different benefits. The choices include ball guides, slide (or prism) guides and wheel guides. A ball guide may be a single square (or profile) rail, the patented Thomson dual rail or round rail. The wide choice available ensures a solution can be optimised for a particular application and to meet lifetime requirements.
In small scale applications such as lab automation, medical instruments or 3D printing, a linear motion system typically only has to handle light loads but absolute precision, high repeatability and a small footprint may be critical. Air grade aluminium extrusions can be used and are easily connected in the necessary planes of motion. In these applications a round rail guide may be preferred for its low friction and smooth operation and the high precision required can be proven at our factory prior to installation in the machine.
Economical transport of loads in harsh environments can be important in factory automation applications such as packaging and material handling. Speed and long stroke length are often required and the Thomson Movopart range offers stroke lengths of up to 12m for loads up to 7500N. Options include belt or ball screw drives with either ball or prism guides. These devices can be used where the whole length of the drive cannot be supported and have a corrosion resistant steel metal band which is kept in place by magnets, to prevent dust and dirt from entering the inner working parts.
The prism (or slide) guide units provide very quiet operation, can handle wash down and are well suited to harsh environments. Because the prism guide runs along the extrusion it has no need for additional bearings and so makes a very cost effective solution for long lengths. Lubrication felt seals ensure a very long lifetime for prism guide systems with light duty cycles, however, for heavier duty cycles a profile rail ball guide is preferred.
Thomson’s on-line Linear Motioneering design tool shows lifetime and safety factors to help engineers identify the best configuration.
For extremely high-speed, high-throughput applications the use of wheel guide technology can achieve up to 10 m/s as there are no recirculating elements. The wide spread of the wheels further makes this style of linear motion system ideal for taking up high moment loads. The Thomson WH120, for example, provides a solution for material handling applications up to 12m where high accuracy, high speed and handling of large side loading are required.
In areas such as machine tool material handling or automation assembly, where a heavy-duty, heavy-load, play-free solution is required, the patented Thomson ball guide provides the ultimate solution. It has large load-bearing balls complete with a typically square rail wide arrangement of ball guides. This enables more power in a compact design to carry large loads and handle high load moments.
The Thomson WM range has bearing blocks that are dynamically transferred within the system at pre-defined locations to support the screw along its whole length for input speeds of up to 3000rpm and stroke lengths of up to 12m without whipping effect. It can be supplied with a single ball nut or, to eliminate completely any play in the carriage, a double ball nut solution.
In one application with a 5m stroke vertical lift, a counterbalance of air had been designed into the system to hold the sliding load. The use of a pre-engineered WM linear motion system meant the slide, brake, gearhead and switches could be ordered against a single part number and the counterbalance could be eliminated.
Pre-engineered linear motion systems can incorporate options such as central lubrication systems to ensure the easiest, fastest maintenance and stainless steel parts to suit hygienic applications along with food grade lubricants. Highly effective seal system options ensure reliable, long-term operation in even the harshest and dustiest of environmental conditions. For applications with high side loads, the Thomson MLSM has ball guides which are separated and positioned at a 45 degree angle.
Most requirements can be met from ‘standard’ product ranges but customised solutions are also available even in very small quantities. Whether there are specific space constraints, motor or gear requirements, Thomson can engineer the ideal, pre-tested solution.
Using a pre-engineered linear motion system makes in-depth expertise and advanced technology solutions readily available to machine builders. The systems are fully tested, alignment issues are eliminated, footprint is reduced compared to some alternate bespoke designs, life calculations are exceptionally easy and the clear support of a single solution provider is available.
No matter what level of precision and repeatability or whether small-scale, light operation or heavy duty, heavy load performance is required, a pre-engineered solution can be optimised for the application, with demonstrable benefits in reduced design risk, time to market and manufactured cost.
Pre-engineered linear motion systems can help ensure performance and reduce cost, risk and time to market
In small scale applications, the load may be light but absolute precision, high repeatability and a small footprint can be critical
Using pre-engineered linear motion systems makes in-depth expertise and advanced technology solutions readily available to machine builders