This article from HepcoMotion describes how wheel-type linear guides can provide the load-carrying capacity, longevity and low cost of ownership required for heavy-duty handling and pick-and-place applications.
When designing systems for heavy handling and pick-and-place applications, choosing the right linear motion technology can be overwhelming. With such an extensive selection available, the decision often comes down to wheel versus recirculating ball bearing technologies.
Considerations in addition to satisfying the application requirements will, of course, include price and delivery but, often to a lesser extent, assembly time and long-term maintenance are relegated down the list of requirements, as cost issues can take over. The hidden costs can then sometimes be ignored, especially if some of the components can be made in-house by the customer or contractor. In considering the total cost, labour time associated with installation and long-term maintenance should also be included. How much work is the customer willing to undertake with respect to fitting the guidance system to machined steel beams? How easy will access be when the system is installed? What about spares? What is likely to fail first and how easy is it to change the failed part? A properly sized system can last the lifetime of the machine, but this can only be guaranteed by using quality parts.
When analysing specific application requirements, the Hepco HDS range can prove versatile. With its extensive variety of components, the HDS range can meet design needs from simple to sophisticated systems.
At the heart of the HDS family is the concept of a rigid aluminium beam to accommodate the attachment of the system's single-edge precision and commercial plain or rack-cut slides. There are, in fact three sizes of beam: the standard version for medium- to heavy-duty gantry X-axes 130mm wide x 220mm high; the compact beam for Z-axis requirements; and now the much larger 200mm wide x 300mm high beam for heavy-duty gantries
Key features include:
- Versatile construction beam in two standard sizes, plus a compact version
- Slide in single lengths up to 4m. Longer systems can be achieved by joining lengths
- Single-edge slides for best load spacing, integral rack drive or plain
- Two types of bearing elements; range of double-row ball bearings up to 128mm diameter for high-load, high-speed, maintenance-free or blocks containing four needle roller bearings for high load where space is an issue
- Range of pinions to suit, complete with locking bush
- Loads to 40kN
- Very high speeds – 5m/s is not unusual
- Low-friction vee bearing/slide arrangement
- High-stiffness beams can be used over long lengths unsupported
- Continuous lubrication option available through cap wipers
- Quiet operation
- Works in any plane
The rigid beam and drive capability make the HDS system suitable for gantry robot design or driven carriage assemblies. While rack-driven systems are often preferred in gantries, belt-driven linear elements are easily accomplished from a standard product. The HDLS product uses single-edge vee slides attached to the beam. The hollow beam, in turn, allows for return of the belt, while the end box design enables easy attachment of the motor and pulleys. This arrangement is available as a complete product.
In addition, the HDS system is also suitable for many cutting, lifting and handling applications in automotive and general industries where customers need to integrate the components into their complete machine.
Aluminium alloy construction beams offer a lower overall installed cost alternative to steel sections. While they do not have the inherent strength of steel sections, when assembled and supported, they will provide more than adequate rigidity and accuracy for even heavy-duty pick-and-place applications. There is also no need to machine steel beams and fit slides, as the beam design will accommodate the slides fitted directly to the corners.
The Hepco heavy-duty steel slides are shown fitted to the standard heavy-duty aluminium beam. This is especially useful in long-length applications, where typically the time and precision required to set recirculating ball bearing type systems can be hours due to the high accuracy required to achieve satisfactory operation. In contrast, the compliance of the wheel technology utilised by the HDS system allows a slight reduction in the overall accuracy setting required.
HDS systems can be shipped as assembled units, complete with drive transmission capability, and ready for installation, which reduces overall assembly and installation costs.
What importance does the customer place on required maintenance? The answer seems somewhat obvious, but the do-it-yourself approach often taken by customers can, in the long run, be costly in terms of reliability and long-term maintenance.
The operating environment must also be considered; not all environments are conducive to achieving long life. Certain cutting applications produce debris that can break down many recirculating systems and cause them to fail, particularly if proper maintenance and re-lubrication is not carried out. HD wheels are normally fitted with cap wipers, which help to prevent debris from contacting the guide wheel, and also provide a lubrication.
A typical XZ gantry system would be constructed using the high-strength aluminium beam 220 x 130mm, together with 95mm diameter bearings. The larger beam (200 x 300mm) that could be used for the same application where higher capacity is needed normally uses 128mm diameter bearings, and provides a capacity of 6 tons. The smaller of the two beams can also be used as a Y-axis, and for lighter load applications, the compact beam is an economical choice. Newly developed for Z-axis applications is a high-capacity telescopic system axis, which is useful where ceiling or head height is restricted.
Such applications also benefit from an integral rack drive incorporated into the slide, which saves on the cost and time of installing a separate rack and aligning it accurately. Continuous lubrication is provided for both vee bearings and rack/pinion.
The Hepco HDS range is suitable for most high-load applications where cost and performance are both important considerations. Due to its ease of installation, low maintenance and capability for achieving long lengths, it is an excellent choice for heavy-duty automation and pick-and-place gantry systems. A wide range of accessories and options make the HDS system extremely versatile, and HDS systems can be purchased ready-assembled for quick installation, or as individual components for custom designs.
Furthermore constant additions are being made to the range to provide even more choice; the addition of a ball screw-driven version utilising the compact beam is one such example. This is available as a standard product, HDCS, and has been incorporated into the latest HDS catalogue.