1. Field of the Invention
The present invention relates to a cooling/lubricating device for a machine tool, and in particular to a cooling/lubricating device of a machine tool feed shaft for cooling and lubricating the feed shaft of ball screw or the like and bearing in machine tools of machining centers or the like.
2. Description of the Related Art
In numerically controlled (NC) machine tools of machining centers or the like, the feed shafts in ball screws or rotating drives of main spindles and the like have attained high speeds recently, and the evolution of heat leads to elevated temperatures, resulting in thermal deformation and thermal displacement. Cooling liquids or the like are therefore provided to cool rotating shafts and bearings in particular so as to prevent spindles, feed shafts, and the like from heating up. In addition to such cooling, it is also necessary to properly lubricate the bearings of rotating shafts.
Because of the considerable increase in the temperature of spindles, cooling and lubricating measures are taken in response to the increase in the spindle rotating speed sooner than with the feed system. However, given the increasingly faster speeds of feed shafts recently, there is a need to ensure stable operation in response to such higher speeds. For example, in machining centers and the like in which light alloys such as aluminum alloys are machined at high speeds, it is necessary to ensure the high speed feed of the three X, Y, and Z shafts which are feed shafts.
There is thus demand for structures that would supply a cooling liquid to the feed shaft in order to prevent increases in temperature in the same manner as for main spindles, and there is also demand for effective cooling and lubricating of bearings, where feed shafts rotate and are supported, in response to higher speeds. Various types of cooling measures have conventionally been adopted to a certain extent to deal with feed shafts related to machine tools. The most often used cooling method is to dispose a pipe along the entire length through the center of the feed shaft, form spaces that are divided on the inner and outer peripheral surfaces of the pipe, and feed a cooling liquid into the spaces, bringing about cooling through the circulation of the liquid by its supply and discharge through one end of the feeding shaft.
The portion, where the cooling liquid is supplied and discharged, is the support that supports the feed shaft at one end of the feed shaft. In terms of cooling technique for these structures, a ball threaded cooling structure suitable for lathes, for example, is known as a technique preceding the recent trend toward greater speeds (see Japanese Laid-Open Utility Model Application 62-32256 for example). Cooling structures which can be adapted to transfer mechanisms such as machine tool tables are also known (see Japanese Patent Publication 4-80265 and Japanese Patent No. 3448732 and Japanese Laid-Open Patent Application 2007-139190 for example). Theses are simple structures which are intended to deal with the higher fast-forward speeds of transfer mechanisms, and have also been built as devices with better maintenance to prevent cooling fluid leakage.
Examples which have been adapted to machine tools such as large-scale machining centers are also known. In large-scale machining centers, the overall length of the structure is longer, and the feed shaft is also necessarily longer. The resulting increase in the level of thermal displacement is considered a problem. Examples of measures taken include cooling devices in which a jacket is formed at the rear of the feed shaft to provide a cavity, and a cooling liquid is supplied and discharged through the jacket (see Japanese Laid-Open Patent Application 2001-108052 for example).
All of these conventional examples are structures in which the cooling liquid is supplied and discharged at the same end of the feed shaft, and as such, maintenance becomes a consideration. In another known technique, the ball nut is cooled, and the same liquid passes into the bearing cone of the bearing through a through hole in the bore threading to cool the bearing (see Japanese Patent No. 3721264 for example).
In terms of lubrication, meanwhile, there are various ways to lubricate the bearings that support spindles, feed shafts, and the like. The bearing employed for feed shafts is a ball bearing. When the feed shaft rotation accelerates, the bearing becomes a heating element, causing the feed shaft to axially expand. It thus becomes necessary to cool the feed shaft as noted above, but proper lubrication is essential at the same time.
Generally, in terms of lubrication, lubricants are individually supplied while the flow to the bearing is properly controlled, to ensure greater longevity. A known example of a lubricating technique for machine tools is a structure in which a rotating shaft pre-coated or pre-filled with a lubricant is used, the lubricant in the rotating shaft is released through centrifugal force, so that the lubricant is supplied to the bearing (see International Patent Application WO 01/031215 for example).
As described above, in conventional methods for cooling feed shafts, the cooling liquid flows along the entire length of the feed shaft, and the cooling liquid is furthermore supplied to and discharged at the end of the shaft. It was noted above that there are various ways to lubricate the bearing that supports the feed shaft. However, the cooling and lubrication is done separately in virtually all the conventional techniques.
The cooling and lubricating are conventionally handled by different methods. Separate pathways are thus formed. Such a structure involves two systems that are different in some way, contributing to less favorable maintenance and greater costs. In the structure in Japanese Patent No. 3721264, the bearing is also cooled, but the structure is complicated because the cooling liquid flows through the bearing from the bearing cone side toward the bearing cup, a rotary joint is needed, and so forth. This is not a structure in which cooling is brought about by the flow of the cooling fluid along the central axis of the bearing upon the feed shaft being cooled by the reciprocal cooling liquid flow. The cooling effects are therefore not necessarily sufficient in structures where the cooling liquid is released on the bearing cup side through centrifugal force.