1. Technical Field
This invention relates generally to linear motion assemblies, and more particularly to linear motion assemblies having wipers and scrapers and to their method of assembly.
2. Related Art
Linear motion assemblies, such as ball screw assemblies, for example, are used to effect linear actuation in various industries, such as machine tool, automotive, aircraft and aerospace, for example. Typically, a commercial ball screw assembly includes a screw with a continuous external helical ball groove and a ball nut with a continuous internal helical ball groove. The external helical ball groove of the ball screw and the internal helical ball groove of the ball nut are configured with substantially identical continuous and uninterrupted leads (turns per inch). With the ball nut received coaxially about the ball screw, the respective internal and external helical ball grooves are arranged opposite one another in radially aligned relation and a plurality of balls are disposed in a continuous helical ball raceway formed between the aligned internal and external helical ball grooves.
Typically, an elastic wiper and relatively rigid scraper are provided within counterbores at opposite ends of the ball nut. The scrapers are located and extend axially outwardly from respective wipers, such that the scrapers have direct exposure to the external environment, while the wipers are located and extend axially inwardly from the scrapers and are shielded from the external environment by the scrapers. The scrapers primarily function to prevent the ingress of heavy external debris and to break-up debris, such as ice or dirt, for example, as the screw and nut translate relative to one another. On the other hand, the wipers primarily function to wipe lubrication along the screw during relative translation, and in doing so, act to push the lubrication axially inwardly away from the opposite ends to prevent the egress of the lubrication from the ball nut. Accordingly, the scraper acts to keep contamination out of the ball nut, while the wiper acts to keep lubrication in the ball nut.
If debris is able to find its way past a scraper, the debris is then brought into contact with the wiper, which as explained above, functions to direct matter inwardly into the ball nut. As such, any debris encountering the wiper is then pumped inwardly into the ball nut, which over time can shorten the useful life of the ball screw assembly. This, of course, can lead to increased maintenance, which in turn means downtime, and further can increase component cost due to the need for potential replacement of parts.
In addition to the above, known scraper and wiper assemblies occupy a required amount of axial space, which generally approaches the combined axial distance of their individual axial lengths. Of course, in many applications, particularly those sensitive to weight, space is generally at a premium, and thus, any space savings that can be gained is generally welcomed.
Further yet, known scraper and wiper assemblies require separate retention mechanisms for each component, thereby adding to the complexity of the designs of the separate components, and further requiring added expense to provide separate retention features. For example, it is known to form interlocking keys on both the scraper and wiper to prevent relative rotation therebetween, and further, to use a separate anti-rotation device, such as a set screw or tang on the scraper, for example, to prevent relative rotation between the scraper and the ball nut. As such, having to incorporate multiple anti-rotation mechanisms inherently adds cost to the individual components, as well as adding cost to the process for assembly.
Accordingly, scraper and wipers assemblies used in linear motion assemblies can be improved to enhance performance, to extend their useful life, and too reduce space requirements and total cost.