THK Is the First Linear Motion Manufacturer to Earn TÜV SÜD Certification! Our Certified LM Guide Testing Methodology

The LM Guide, Supporting Industry the World Over

What Is an LM Guide?

The LM Guide (Linear Motion Guide) first came onto the market in 1972 as the result of THK applying its original technology to integrate rolling motion into the linear motion units of machines, a feat long considered to be extremely difficult. The use of rolling motion in linear motion components has since then significantly improved the mechanical performance of mechatronic equipment in areas like precision, high-speed performance, and energy savings.

The LM Guide’s Basic Dynamic Load Rating

Now, let's take a closer look at the LM Guide’s basic dynamic load rating. The basic dynamic load rating (C) indicates the load for which the nominal life (L) is 50 km for an LM Guide using balls or 100 km for an LM Guide using rollers when a group of identical LM Guide units independently operate under that load when it is applied in a constant direction and magnitude. It is calculated based on various LM Guide parameters and varies by model number and size. The basic dynamic load ratings listed in our catalog are, in turn, used to calculate service life during LM Guide selection and design.

Basic Dynamic Load Rating and Service Life

The constant linear motion of an LM Guide subjects its raceways and rolling elements to loads that cause metal fatigue and, ultimately, cracking. When these cracks spread to the surface, they ultimately cause scale-like pieces of metal to peel off in a phenomenon called flaking (or spalling). The service life of an LM Guide is the total distance it can travel before this flaking occurs. The distance that 90% of LM Guide units can travel without flaking is called the L₁₀ service life. It is calculated using the simple theoretical formula L₁₀ = (C/P)3 × 50 (km). In this formula, C is the basic dynamic load rating and P is the load applied to the LM Guide. Thus, if the applied load P is held constant, increasing the basic dynamic load rating C also increases the distance that an LM Guide can travel before it reaches its service life, which in turn reduces the frequency and cost of making replacements. However, choosing an LM Guide model that exceeds the required specifications can prove disadvantageous if it is incompatible with spatial limitations or would increase the weight of a machine. This makes it important to choose an LM Guide that is both compact and possessed of a large basic dynamic load rating.

Verifying Reliability with Empirical Testing

Up to this point, we’ve covered the relationship between an LM Guide’s basic dynamic load rating and its service life, but we still need to empirically demonstrate that the numbers we calculate for the former are correct for each model number if we’re to deliver reliable products to our customers. Let’s take a closer look at the empirical testing THK does on the LM Guide for this purpose.

TÜV SÜD

While THK rigorously controls the empirical testing it performs, we have also obtained third-party certification from TÜV SÜD to enhance its reliability even further. TÜV SÜD, a global enterprise based in Munich, provides inspection, certification, testing, and consulting services for the automotive, industrial machinery, construction, energy, and medical equipment fields, among others. Many manufacturers in Japan alone have certifications in various areas. When it comes to machines, electronic equipment, and medical products, these certifications serve as proof of a product's safety and functional effectiveness. Some of you reading this right now may have seen the TÜV SÜD certification mark on familiar electronic components you encounter daily.

TÜV SÜD Certification

THK's TÜV SÜD certification includes the following.

Testing Specifications

THK has established testing specifications for evaluating basic dynamic load rating. These specifications were created in line with DIN 631,¹ DIN/ISO 14728-1,² DIN/ISO 17025,³ and DIN/ISO 281⁴ to ensure compliance with international standards and to ensure further reliability.

Testing/Evaluation Machines

The testing/evaluation machines used for our empirical testing can evaluate multiple LM Guide units at a time and are designed to minimize or eliminate factors that impact service life. Our qualified and authorized facilities possess several of these machines.

Test Conditions

Test conditions encompass various factors that can impact the service life of an LM Guide. At THK, we identify all of these factors, eliminate their impact, and maintain strict tolerances for each of our testing conditions that are listed in the aforementioned testing specifications in compliance with DIN 631.

Items Checked

Our empirical testing encompasses a variety of measurements and items for confirmation. We rigorously measure and manage each item to ensure that it meets the tolerances of our established test conditions. To ensure that these processes are performed in compliance with our testing specifications, we have created a sizable set of work instructions and checklists, which we use to maintain consistency in our work and to ensure that we obtain high-quality, reliable results.

Evaluators

The evaluations we do in our empirical testing are performed only by qualified personnel from the testing department who have received the appropriate training. Permitting only trained personnel to perform these tests increases the reliability of the results they yield.

Measuring Equipment

The measuring equipment used in our empirical testing is regularly calibrated and traceable according to national standards to ensure constant dependability.

Global Evaluation Structure

THK has established a global evaluation structure in which all locations that possess testing equipment, including overseas plants, are able to perform the same evaluations. Our test specifications and work instructions ensure that the quality of our testing/evaluations is the same at all of our locations.

Pursuing Greater Reliability through TÜV SÜD Certification

The activities described above make THK’s LM Guide products highly reliable and allow our customers to use them with confidence. Continuing to undergo the assessments needed to maintain TÜV SÜD certification in particular for nearly 20 years demonstrates that THK's products satisfy international standards of safety and quality. By inviting TÜV SÜD's rigorous scrutiny, we continue to offer customers added value in the form of ever greater reliability. As a pioneer in linear motion systems, THK will continue to pursue technological innovation and quality improvements as we strive to provide ever more reliable products.