What is required is a stable rigid mechanism, with no bending moment. Accuracy can be very high because the bearings have such smooth motion. They often use servomotors to drive the bearings, to make incredibly fine adjustments for processing microscopic features. When controlled by a servomotor, such motions can be invisible to the naked eye.
Supporting such machines’ capabilities are the most smooth-rolling precision linear guides in the IKO range, particularly the non-recirculating BSP, BWU and CRW products.
They accomplish this partly through a simple design, single linear caged bearings consisting of ball or roller elements running along inner and outer tracks. The bearings are arranged in two parallel tracks, one on each side of the slide, to support the weight of the table (or carriage) and its mounted load as it moves.
This design provides completely smooth and very precise reciprocating motion with no backlash over relatively small distances. As the bearings remain in the same orientation and do not circulate within the table, there is no skipping or juddering caused by a rolling element emerging from the circuit and being compressed on to the bed. For the same reason, the reciprocating movement is very quiet. Maximum speeds of 30m/min can also be achieved.
By the same token, since the bearing cages support the carriage, their length sets the upper limit for bearing stroke. Stroke lengths for bearings vary, with the largest standard sizes up to about 68mm for BSP and BWU, and approximately double that for CRW models.
However, IKO can alter the length of roller strip on a custom basis to increase stroke by up to 25%, however such a change will reduce its carrying capacity, as each rolling element will have to take a greater proportion of the load. From that point of view, IKO can help designers optimise the system for their particular application, within the parameters of a fundamental design trade-off between stroke and load capacity.
A further advantage of the precision linear slide units’ design configuration is extremely accurate motion. Parallelism of the BSP limited linear motion type precision linear slide units at the table centre is 3micron up to 18mm travel, and 6micron up to 80mm travel (for BWU it is 4micron up to 50mm length, and 6micron up to 120mm length). Compared to standard product, its performance is better at the shorter end, and up to four times as good for longer travels.
The most cost-effective model of precision linear slide is the BSP product, which consists of balls mounted in a pressed stainless steel unit. BSP models range from 9-63mm in stroke length, carrying basic dynamic load rating capabilities ranging from 93N to 1,410N & basic static load rating capabilities ranging from 42N to 992N.
A more heavy-duty option is the BWU unit, which features balls inside a forged stainless steel casing. BWU models range from 3mm-68mm in stroke length with basic dynamic load rating capabilities ranging from 154N to 8,050N, and basic static moment capabilities ranging from 181N to 12,100N.
The most rigid of all are the CRW models that combine forged steel rails with cylindrical crossed rolling elements. The wide range of CRW models range come with a variety of stroke lengths and basic dynamic and static load ratings that are too numerous to mention in an article such as this.
One unintended consequence of the free-running design is that, in standard models, the position of the bearing cage can wander over the stroke length, particularly at high reciprocation speeds and when mounted in a vertical (Z) orientation, the force of gravity often causes the bearing cage to end up out at the bottom end of the stroke. This is called cage creep, and can affect the performance of the bearing. To prevent this, BSPG and CRWG models of IKO precision linear slides incorporate a rack and pinion, the former in the bed, the latter in the table, to prevent slippage.
The high precision performance of the linear ways require additional care in installation. The bed and rails must be installed by a skilled technician. In addition, mounting surfaces for the CRW beds must be ground before installation.
While IKO prizes quality over pricing, one thing for customers to keep in mind when buying precision linear ways is how many parts are included. While, for historical reasons, many competitors sell these parts in half packs – two ways and one cage – IKO always sells linear ways as a complete kit of two cages and four ways. For that reason, a price that is 75% higher for an IKO pack for example when compared to a competitor’s item, might actually prove to be a relative bargain, as two sets of the competitor’s product would be needed to make up the same quantity as IKO’s offering.
By offering the right bearings in an installation-friendly manner, IKO aims to meet & often exceed its customers’ needs.
Contact IKO UK today at 01908 566144, or email enquiries@iko.co.uk to discuss your motion control needs. Alternatively, visit the IKO website.
