September 2021

Selection criteria During the design of a newmachine, choosing the correct guide system is one of the fundamental decisions to make. Factors such as speed, positional accuracy, payload and environmental conditions play a key part in the decision for or against a certain design of guide system. In this overview, we show how different guide products from HepcoMotion are able to meet each of these factors. Drive Type: Positional accuracy versus speed Before approaching“which linear guide?”, it is important to consider requirements of the application in terms of the drive type. The most common drive types are screw, rack & pinion, belt drives and linear motors. Each of these types of drive has its pros and cons, giving them strengths in different areas of use. In many applications, positional accuracy and speed are key parameters that determine the most suitable type of drive. This is not the only reason for the increasing popularity of linear motors. Linear motors enable high speeds in combination with precise movement. Above all, however, linear motors enable individual control of carriages. This gives greater flexibility in a production cell, where on-the-fly changes are sometimes required on a daily basis. Nevertheless, there are other factors to consider; the original Beckhoff XTS system (one of the market leaders in linear motor drives) is designed for transport of light payloads. HepcoMotion’s specially developed guidance system, GFX, used in combination with the XTS linear motors, overcomes this limitation. An XTS system used in combination with GFX is capable of a 50N capacity at speeds up to 4m/s, with a repeatable accuracy of less than ±10 μm. However, it should be considered that this type of system requires higher initial investment due to its complex electronics. This initial investment may be worthwhile in many cases, but not all. When one looks at traditional drive systems, it is still important to be clear about the goals to be achieved. For example, a ball screw will provide a high level of accuracy – typically ±0.05mm. A toothed belt drive will achieve approximately ±0.1mm and for a rack and pinion drive an accuracy of ±0.3mm is assumed. In terms of speed, a ball screw cannot achieve the same speeds as a belt drive and its length is limited based on speed. Rack and pinion drives are also limited by speed, but do not have the same limitation on length. When specifying a drive system, you have to balance several features – you cannot look at each element in isolation. A short stroke can be achieved more quickly with a screw drive because of the high rate of acceleration required. Racks and pinions are more commonly employed on longer axes where the rate of acceleration can be lower to achieve the same maximum speed. The installation orientation of the components is also a consideration. In vertical applications, some drives may offer an advantage due to their high capacity. Belt drives may also be suitable, providing the tensile capacity of the belt is sufficient to support the payload. Additional support may be required, but can encroach on the available space envelope beneath the payload. An exception to this is the DTS+ and DTS2 product ranges, which are designed such that they can operate in any orientation. Rack drives are commonly used in multi-axis systems. Z-axis assemblies can be arranged such that the beam and slides are the moving component and the motor and carriage plate remain fixed, reducing the mass of moving components. Where a customer requires a complete gantry or multi-axis solution, HepcoMotion can deliver its products as a complete system, with drive and axis connections fully specified. In the case of ring and track solutions, the DTS product range is unrivalled in its market. COVER STORY Linear Motors can provide independent carriage movement and operates at reliably high speeds. For an application that includes curved motion – either as a combination of straights or rotary motion, PRT2 or a fully supplied system such as the DTS range will be the right choice.