In modern machines with long axes, gantry systems, or tight tolerance requirements, the choice of rack is crucial for precision and efficiency. The ATLANTA Method replaces the traditional selection by quality classes with a data-based selection of precisely measured racks. This whitepaper shows how overall pitch errors can be significantly reduced, as- sembly accuracy improved, and new design freedoms created.
White paper ATLANTA
RACKS IN THE AGE OF INDUSTRY 4.0
Racks have been central elements of linear technology for decades. They enable the precise conversion of rotary into linear motion and are used in countless machines and systems. However, despite the maturity of this technology, its practical application, espe- cially for long travel paths, regularly encounters technical limits. A central problem lies in the accumulation of manufacturing-re-lated tolerances, in particular the so called Total Pitch Error (TPE). This describes the deviation of the actual tooth pitch along the length of the rack from the ideal target pitch.
The TPE can be positive or negative and varies depending on the quality class of the rack:
– for a quality 5, the permissible total pitch error is only ±0.030 mm/m
– for quality 10, it can reach up to ±0.200 mm/m
Especially with long axes, these deviations accumulate across multiple racks. In practice, this can lead to the rack’s mounting holes increasingly deviating from the predefined hole pattern in the machine bed, causing misalignment.
With the advent of Industry 4.0 and the concept of the digital twin, a paradigm shift has occurred.
At ATLANTA, we use these possibilities to characterize each individual rack and make its data available for planning, assembly, and maintenance.
The result:
- A precision level previously unattainable in this field
- New applications for linear axis design, such as gantry systems
- Tailored solutions for long travel paths
Traditionally, racks are selected according to quality classes (e.g., Q6, Q8, etc.), assuming that racks of the same class behave identically.
Example with a 6 m long axis, using 1m racks, Q6, Module 4
| Number or racks: | : | 6 |
| Total pitch error: | : | 0,034mm |
| Connection error per rack joint: | : | 0,025mm |
Maximum possible deviation:
Number of racks × total pitch error per rack + number of joints × connection error per joint
= 6 × 0.034 mm + 5 × 0.025 mm = 0.329 mm ≤ allowable max. deviation of the full axis
To determine the maximum possible TPE of an axis, the permissible pitch error per rack (per chosen quality class) is multiplied by the number of used racks. Additionally, the potential errors at the joints must be considered. This yields a theoretical maximum value, which in a worst-case scenario represents the largest possible deviation of the axis.
Pic. 1 Uncertainty range (Worst-Case-Scenario)
In practice: the longer the axis and the more racks combined, the larger this uncertainty range becomes during assembly. As a result, rack holes may no longer align with the intended mounting points in the machine bed. In extreme cases, racks cannot be mounted at all. To avoid these risks, designers often have to resort to higher and significantly more expensive quality classes.
To overcome these limitations, we have fundamentally revised the traditional approach and systematically applied the digital twin concept to racks.
A digital twin is a virtual replica of a real component that makes all relevant geometry and quality data digitally available.
At ATLANTA, this means: we don’t just manufacture racks, we also provide each one with a digital profile containing all its pro- duction characteristics. This information is available to users throughout the entire product lifecycle, from design to assembly to maintenance.
Pic. 2 Measuring process of an ATLANTA rack
3.1 Implementation:
Each rack receives a unique serial number and matrix code for identification. At the end of production, every rack is precisely mea- sured. Individual TPE values and further geometric parameters are recorded. The TPE is stored digitally in the ATLANTA Cloud. Via the web-based ATLANTA ProductScan, designers and maintenance staff can access this data anytime, directly integrating it into selection, design, or service tasks.
Instead of working with assumptions and tabulated values, actual measurement data of each rack is available. The web-based ATLANTA Mapping Tool automatically sorts racks so they can be combined in an optimal sequence. TPE values with positive and negative deviations can be arranged to compensate for each other. The result is a defined, application-optimized assembly order. This drastically reduces overall deviation on long axes, something previously impossible.
Pic. 3 Course of the Total Pitch Error of unsorted (red) and sorted (green) racks of a 25m long axis. The blue line indicates the worst-case scenario for unknown or unmeasured Q6 racks.
The ATLANTA method opens up new opportunities for machine builders to design linear axes with greater precision and cost efficiency.
Pic. 4 Data of a rack from the ATLANTA-Cloud
Targeted component selection based on real measurement data
Designers can select the optimal component without relying solely on expensive higher quality classes. Exact TPE values allow precise alignment with system requirements.
Planning reliability and simplified assembly
Factory numbering and cloud-based rack data enable a defined, optimized assembly sequence. Time-consuming adjustments on site are eliminated. Mounting holes and fixing points can be precisely prepared.
Efficient maintenance and reduced downtime
In case of maintenance, replacement racks with identical TPE values (“clones”) can be ordered and installed, minimizing adjust- ments and significantly reducing downtime.
Extended system concepts and cost savings
By compensating TPE along long axes, designers can rely solely on electromechanical systems for required precision. Additional positioning systems may no longer be necessary, reducing cost and allowing flexible axis extensions without precision loss.
Gantry systems
Gantry systems consist of two parallel, usually synchronized axes that move a cross beam precisely. With the GANTRY function in ATLANTA’s digital application, two rack runs can be selected whose TPE curves best match. This minimizes differences between left and right sides, allowing nearly stress-free assembly, increased precision, and longer system life.
Defined TPE – tailored for long travel paths
A major advantage of the ATLANTA method is targeted rack selection for long-travel applications. From the database of precisely measured racks, combinations are selected whose TPE curves complement each other. Both inter-rack deviations and intra-rack error progressions are considered in the optimization.
Our long-term partner, Vansichen Linear Technology (known in Germany as SimKon by Vansichen), illustrates this.
The Belgian company specializes in linear axes for robotics and portal systems and has implemented over 1000 projects.
For a robotics customer, a 25-meter-long robot travel axis had to be realized with:
- Maximum precision over the entire distance
- No additional measuring technology
- Economical components
Implementation with the ATLANTA method:
- rack module4, quality 8 was selected
- before assembly, each rack matrix code was scanned with ATLANTA‘s Mapping Tool
- TPE values were obtained from ATLANTA‘s Cloud
- an optimized assembly order was calculated to minimize overall deviations
Results:
The total pitch error on 25 m has been optimized within 70μm using quality 8 racks; using a random assembly of same ATLANTA racks the total pitch error would have been 140μm.
As reference the maximum possible deviation on 25m for quality 4 racks of any manufacturer is 375μm
Pic. 5 A 25 m long Roboter-Axis of Vansichen Linear Technology
Thus, the overall deviation was almost halved, without additional measuring systems, simply through intelligent use of the racks’ digital data: moreover, this has been possible using quality 8 racks, see graph pic. 3.
While the traditional method selects racks by quality class and assembles them in arbitrary order, the ATLANTA method relies on precise measurement data for each rack and a targeted, data-driven assembly plan.
With this approach, the TPE over long axes can be drastically reduced without resorting to expensive higher-quality racks. By sys- tematically analyzing measurement data and intelligently combining already produced racks, a new level of mechanical precision in rack drives is achieved: digitally supported, cost-efficient, and application-oriented
ATLANTA is the ideal partner to develop future-oriented linear applications, not a common rack manufacturer.
