In a wide range of applications machine builders are demanding increased accuracy and precision from their production equipment. Simultaneously, increasingly complex automation has created an additional challenge, as the vibration of dynamic machine components can significantly increase vibration of the complete system. Justin Leonard, the-chain director, igus, explains
In a number of industries, including printer design, semiconductor manufacturing and machine tools, cable management systems can be a possible source of vibration. This vibration can be transferred to supporting structure of the energy chain, as well as the moving end or tow arm of the machine. Once it reaches a certain level, the overall performance of the machine can be affected. For machine builders, as well as their customers, factors that limit the capabilities of precision systems must be tackled using cable management systems that minimise vibrations and maximise smooth and precise operation.
In printing, milling, or other high-precision processes, dynamic loads are the typical source of vibration, or ‘chatter’, which corresponds to the relative movement between the workpiece and tool. This chatter not only decreases 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 vibration.
Designing vibration-reducing components
Most cable management systems have a pin-and-bore type connection between the individual links of the energy chain in order to guarantee a secure connection under high dynamic loads. This type of connection also gives the 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 management 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 reduce vibration, many energy chain manufacturers have modified the design by reducing the link pitch length. This upgraded design offers extremely smooth and nearly vibration-free operation, even under high acceleration forces. In igus low-vibration energy chains, which encompass the E3, E6, and E6-1 series, the traditional pin-and-bore design has been replaced by the combination of a short pitch length with an advanced plastic spring element. The flexible connection element reduces the polygon effect due to its alternative geometry.
The advantages of this new design were tested for effectiveness in a 220 million cycle test conducted in the igus test lab. The endurance test was conducted with the E6-29 energy chain system, with focus on the system’s spring link connection. Throughout the test, the connection was subjected to more than 440 million bending cycles, and based on the results issued from the University of Applied Sciences in Cologne, Germany, no measurable wear or damage of any kind was recorded.
Material selection and its impact on vibration
No matter how specialised the design of a cable management system may be, without materials that are properly able to dampen vibration, damage and eventual failure can still occur. Compared to their metal counterparts, plastic materials are much better at damping vibration forces, due to their viscoelastic behaviours. With this in mind, igus developed a material specifically for use in energy chains called, igumid G. This materials a proprietary blend, made up of a reinforced polyamide 6 (PA6) base. Polymer blends such as this 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.
When compared to metal and other plastic energy chain options, igumid G offers a much higher ability to dampen vibration forces. Vibration testing was conducted by the IPA Fraunhofer Institute on the material, which makes up both the energy chains and the spring link connection elements. These tests found that the specialist plastic material offers sound pressure levels of only 37 dB (A), significantly below the values of other material options, which has also been confirmed by experts at TÜV Rheinland. In addition to sound pressure testing, these tests showed a range of other material benefits of igumid G, including high levels of corrosion and wear resistance, and compatibility with the maximum quality standards for cleanrooms, ISO Class 1. ESD versions of the material are also available. Comparison of vibration properties
A study was conducted by the Laboratory for Machine Tools and Production Engineering at the RWTH University in Aachen, Germany to determine and compare the vibration properties of a range of five cable management systems of the same size category. Tested energy chains included an igus E6 and 380 series, along with three from other manufacturers.
The test used a base frame and a highly dynamic linear motor drive, with a force of 14,000 N. The linear motor moved a carriage attached to the moving ends of the energy chain at four different speeds (25, 50, 100, and 200 m/min), and two accelerations (10 and 20 m/s²) over a travel length of 800 mm. Impact of the energy chain’s vibrations were measured with two accelerometers with sampling frequency of 6000 Hz, that were installed on the moving end and the support trough. Data was measured separately for the two directions of travel. Sensor generated signals were analysed in the time and frequency domains. For the time domain, the root mean square (rms) value indicated the vibration energy at the measurement location.
For all the energy chains included in the test, the highest levels of vibration were evident on the supporting trough in the direction of the application axis (z-axis), however, the differences in accelerations had no significant influence on the vibration values. According to the test data, of the five energy chains tested, the vibration values were lowest for the two igus ones.
The results from these tests demonstrate that the E6 and 380 energy chains offer ideal performance with respect to vibration characteristics and smooth operation at all travel speeds and accelerations. On average, the measured vibration was 28 percent lower than that of energy chains from other manufacturers. The igus E6 and 380 demonstrated an effective maximum value of approximately 4 m/s². In contrast, the energy chain with the highest levels of vibration exhibited a value of 5.6 m/s², or approximately 40 percent higher than the vibration exhibited by the tested igus options.
The new E6-1 series from igus is the next generation of the E6 series, which on testing has shown to have the lowest levels of noise and vibration in cable management 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 energy chain design. An example of this would be creating a nested arrangement, which can dramatically increase milling accuracy in certain cases. These nested systems, like the example shown above, 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 situation, an additional mass transforms the kinematic energy from the vibration into thermal energy or a relative motion between two other bodies. Active systems, on the other hand, employ an external energy supply to create a phase-cancelling vibration. Both passive and active systems can effectively compensate for vibration, 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.
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 chain systems in dynamic applications. New solutions, such as the polymer spring link connection for igus energy chain, can significantly contribute towards realising this objective. While other solutions are available, the lowest cost option to create a low-vibration system is to integrate low-vibration machine components.