Customers are demanding increased accuracy and precision from their production equipment across a wide range of applications. By Dan Thompson, product manager for energy chain cable carrier systems, igus Incorporated.
Increasingly complex automation has created the additional challenge of vibration of dynamic machine components significantly increasing vibration of the complete system. In a number of industries—including semiconductor manufacturing, machine tools and printer design—cable carrier systems can be a possible source of vibration.
Cable carrier systems supply energy, data and other media, and as technology increases, so too does the number of cables and hoses that require guidance. As cable carriers guide and protect cables and hoses throughout the motion of the printer, machine tool, etc., vibration of the supporting structure of the cable carrier can occur, as well as at the moving end or tow arm of the machine.
This vibration can negatively influence the performance of a machine once it reaches a certain level. For manufacturers, as well as their customers, factors that limit the capabilities of precision systems must be tackled using cable carrier systems that minimise vibrations and maximise smooth and precise operation.
In milling, printing, or other precise tasks, dynamic loads are the typical source of vibration, which can cause chatter on tools and workpieces alike. These chatter vibrations not only decrease the quality of the print, product, etc., but can also cause increased wear on the components of the machine itself, leading to product defects, system malfunctions and downtime. Because of this, the dependence on low vibration materials and machine components is on the rise in an effort to limit self-generated machine vibrations.
Designing Vibration-Reducing Components
Most cable carrier systems utilise a pin-and-bore connection between the individual links of the carrier in order to guarantee a secure connection under high dynamic loads. This type of connection also gives the carrier system protection against external influences, resistance to high torsional forces, high tensile strength, and high mechanical durability. However, a disadvantage of the pin-and-bore design is the resulting relative motion between the links, which over time can cause wear on moving parts.
In addition, the rolling motion of a cable carrier system exhibits the so-called “polygon effect,” where the chain does not form a smooth rolling motion, resulting in an angular, or polygonal, transition between links. In addition to increased wear, this also results in a “stepping” motion, which can create system vibrations. This can—in a worst-case scenario—result in material failure due to catastrophic resonance. Even in less extreme cases, the vibration caused by the polygon effect results in material wear and decreased accuracy on the workpiece.
To improve upon the design of cable carriers to reduce vibration, most manufacturers rely on a short link pitch to offer smooth, quiet motion. Igus’ low-vibration energy chain cable carriers combine a short pitch length with an advanced plastic spring element to replace the traditional pin-and-bore design. Replacing the conventional pin-and-bore design, the E3, E6, and E6-1 series of energy chains feature a flexible connection element that reduces the polygon effect due to their alternative geometry. This upgraded design offers extremely smooth and nearly vibration-free operation, even under high acceleration forces.
Material Selection And Its Impact On Vibration
No matter how specialised the design of a cable carrier system, without materials that are properly able to dampen vibrations, damage and eventual failure can still occur. Compared to their metal counterparts, plastic materials are much better at damping vibration forces, due to plastics’ viscoelastic behaviours.
The plastic material igumid G, which makes up igus energy chains, is a proprietary blend, made up of a reinforced polyamide 6 (PA6) base. Polymer blends like these are also able to dampen vibrations by using the interface between the material’s components (ie: fibres and other structures blended throughout the base polymer) as a mechanism for reducing vibratory forces.
The new E6-1 series of cable carriers has shown to have the lowest levels of noise and vibration in cable carrier applications due to its material makeup and design. This new generation offers a weight reduction of approximately 30 percent when compared to the E6 series, and exhibits even lower noise and vibration levels. A shortened pitch and “brake” in the stop dog system reduce the sound pressure levels by an additional 2 dB(A). Optimised geometry makes operation of the E6-1 system very smooth, eliminating the polygon effect almost entirely, even at higher speeds and accelerations.
Another option for reducing vibration on machine tools can be provided via special cable carrier design. An example of this would be creating a nested arrangement of cable carriers, which can dramatically increase milling accuracy in certain cases. These nested systems can change the system properties of the machine, and can be combined with additional systems to help minimise or eliminate damaging vibrations. These systems apply external forces to minimise or completely eliminate damaging vibrations via damping or cancelling solutions, differentiated into passive and active systems.
Passive systems attain their vibration damping effect by converting the vibration energy to another form. In this circumstance, an additional mass transforms the kinematic energy from the vibration into thermal energy or a relative motion between two other bodies. Active systems employ an external energy supply to create a phase-canceling vibration.
Both passive and active systems can effectively compensate for vibrations, but also have a cost impact, as these types of systems are typically only available as a customised one-off solution and cannot be transferred to other machinery. The economic use of these types of adaptive solutions is not always viable for the price-sensitive machine tool market; therefore, the primary effort in research and development for vibration-reducing systems going forward should focus on identifying and reducing the component sources of vibration.
Improving Operational Efficiency
As the demands for process accuracy for a range of applications increases, the need for technical advances to reduce vibrations also grows. An important element of a successful strategy is to improve the operational smoothness of energy supply systems in dynamic applications. New solutions, such as the polymer spring link connection for igus energy chain, can significantly contribute towards realising the objective of attaining a low-vibration machine tool. While other solutions are available, the lowest cost option to create a low-vibration system is to integrate low-vibration machine components.