Abstract:
A hooked dust scraper for ball screw unit includes a plurality of tooth portions and corresponding number of hook portions. It is characterized that the scraper is hooked on the nut of the ball screw unit without employing screw engagement so that the ball screw unit associated with this scraper is easy to fabricate, assemble, and detach thereby saving the production and assembly cost.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an improved structure for a scraper to be used with the screw mechanism, in particular, a hooked dust scraper for ball screw unit to effectively prevent possible foreign materials such as dust, culls and adulterates from infringing into the spiral passage of the ball screw unit by removing them in advance ahead of the moving screw nut so as to protect the balls screw unit from excessive abrasion. 
   2. Description of the Prior Art 
   A screw mechanism has been applied in the mechanical engineering field for a long time. Basically the rotating motion of a screw bolt is converted to the linear motion of a nut so as to transmit a working piece. Among the existing screw mechanism the ball screw unit is the best efficient one because the traveling of the nut on the screw bolt is carried out by a plurality of balls rolling along the spiral grooves formed therebetween. 
   However, if the above mentioned foreign materials are stuck on the screw bolt, they might enter the passage of the rolling balls so as to retard the movement of the bolt or even seriously damage the ball screw unit by excessively abrasing the spiral grooves formed between the screw bolt and nut serving as a rolling passage for the balls. Therefore, installation of a scraper to remove the dust to clean the rolling passage is absolutely necessary. 
   A perspective view of conventional a scraper for a ball screw unit is shown in  FIG. 10  in which a screw bolt  1  is couple with a nut  23 . In this structure a scraper  60  is provided for equipping between the contact surface of the screw bolt  1  and the nut  23  at both ends of the nut  23 . The scraper  60  is fixed to the nut  23  with a fixing screw  70  screwed into screw hole  231 . The construction of the scraper  60  formed as such has to undergo a tedious and time consuming machining process by at first drill a screw hole  231  on the nut  23 , then rotating the scraper  60  into the nut  23  on the bolt  1 , then drill a hole on the scraper  60  at the positions corresponding to the screw hole  231  for screw combing the scraper  60  with the nut  23  by a fixing screw  70 . During such tedious machining process, it is probability to happen the defective operations, for example, forgetting to apply one or two screws, piercing accidentally the screw bolt when drilling the screw hole, and unstable installation of the scraper due to its insufficient thickness, etc. 
   For these defects noticeable on the prior art, an improvement is seriously required. 
   The inventor has dedicated great efforts for years to studying and improving these defects and come up with a novel hooked dust scraper for ball screw unit as provided in this invention to eliminate the defects mentioned above. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is to provide a hooked dust scraper for ball screw unit, which can simplify the fabrication and assembly process so as to curtail the production cost by means of a screwless but just only a hook on structure. 
   The hooked dust scraper is the most effective one for removing the foreign materials such as dust, culls and adulterants sticking ahead of the passage of the ball screw unit whose operation relies on the rotation of rolling balls in a spiral groove to push the nut traveling onwards. By attaching the scraper at both incoming and outgoing ends of the ball screw unit to remove the aforesaid foreign materials, the ball screw unit can be operated smoothly and efficiently without the worry of damaging the unit due to excessive abrasion. 
   The main structure of the present invention includes a tooth portion and a hook portion respectively provided at inner and outer sides of the scraper. A plurality of pawls of the hook portion are arrayed along the outer edge of the scraper with a defined pitch such that when the scraper is squeezed beneath the nut of the ball screw unit the pawls may hook on the nut and travel along with the nut without slipping and leave the rest of unhooked pawls maintaining the compressed state thereby enhancing a close attachment of the scraper with screw bolt. 
   In the meanwhile, the pitch size of this gear shaped scraper determines the opened angle between two adjacent pawls, hence a proportional relation exists between the rotation angle of the scraper and the longitudinal linear displacement of the scraper along the screw bolt. In view of this, the present invention reserves a clearance between the pawls of the scraper and the adjacent screw bolt thread. The pitch of the screw bolt and the clearance are designed appropriately such that the longitudinal displacement of the scraper per revolution is less than this clearance thereby eliminating mutual interference between the scraper and the screw bolt during operation of the ball screw unit. 
   Furthermore, in the present invention, the two portions of the scraper is separately fabricated before assembling rather than integrally formed in one piece. With this structure, the scraper is widely applicable for variously sized ball screw unit having different threads sizes or different ball size by only replacing the improper tooth portion for the scraper. 
   Originally, the present invention provides a scraper only applicable for the ball screw unit with end cut through threaded groove. In order to make the scraper of the present invention applicable for the unit with none end cut through thread groove, an improvement is added to the present invention in which forming a slit on the circumference of the scraper by cutting a small part open thereof. When assembling, pull apart the two sides of the slit a little bit and squeeze the scraper into the spiral groove of the desired ball screw unit. In this manner the pawls are exerted by a small compressive clipping force from the slit which in turn serves to shrink the inner diameter of the scraper and further enhance the close attachment of the scraper to the screw bolt thereby upgrading the applicability and dust prevention effect of the present invention. 
   Besides, the tooth portion of the scraper according to the present invention is made of an oil immersed material so as to lubricate properly the ball screw unit when it is in use with this scraper. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiments of the present invention with reference to the attached drawings in which: 
       FIG. 1  is a cross sectional view of a ball screw unit equipped with the hooked dust scraper of the present invention; 
       FIG. 2  is a perspective view of the present invention; 
       FIG. 3  is a cross sectional view of  FIG. 2 ; 
       FIG. 4  is a partial side view of a ball screw unit equipped with the scraper of the present invention; 
       FIG. 5  is a partial front view of a ball screw unit equipped with the scraper of the present invention; 
       FIG. 6  and  FIG. 7  are respectively the second and third embodiments; 
       FIG. 8  is a schematic view showing various shaped slits provided with the scraper of the present invention; 
       FIG. 9  is a schematic view showing various shaped pawls provided with the scraper of the present invention; and 
       FIG. 10  is a cross sectional view of a ball screw unit equipped with a conventional dust scraper. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1  is a cross sectional view of a ball screw unit equipped with the scraper of the present invention. As shown in  FIG. 1 , a scraper  30  is attached to both ends of contact surface between a nut  20  and a screw bolt  10  with a lead L, retaining slots  21  are formed in the nut  20  at aforesaid both ends of contact surface by cutting so as to fasten the scraper  30  to the nut  20 . 
   Referring to  FIG. 2  and  FIG. 3  which show a perspective and a cross sectional views of scraper according to the present invention respectively, the circular scraper  30  includes essentially a tooth portion  31  formed along its inner circumference and a hook portion  32  formed along its outer circumference. Each hook portion  32  has a plurality of pawls  321  protruded outwardly from the outer edge of the scraper  30 , while the inner tooth portion  31  is in mesh with the thread of the screw bolt  10 . A fissure  33  is formed between the tooth portion  31  and the hook portion  32  so that the pawls  321  can be squeezed beneath the nut  20  to engage with the retaining slot  21  following the movement of the nut  20 . In order to facilitate the aforesaid squeezing action, the contact surface (not shown) between the pawls  321  and the nut  20  is made into a planar or curved one. 
     FIG. 4  and  FIG. 5  are respectively a partial side view and a partial front view of a ball screw unit equipped with the scraper of the present invention. As shown in  FIGS. 4 and 5 , the pawls  321  are arrayed along the outer edge of the scraper  30  keeping a distance of P (pitch) apart from each other. When the scraper  30  is squeezed beneath the nut  20 , the pawls  321  are shrunk towards its own center. In order to avoid mutual interference between the scraper  30  and the screw bolt  10  having the lead L, a clearance δ is reserved between the teeth of the tooth portion and the adjacent thread of the screw bolt  10 . With this consideration, the pawls  321  may be easily squeezed into the corresponding retainer slot  21  and fastened closely to the nut  20  by reciprocally adjusting the pawls  321  within an angle of P/2 as shown in  FIG. 4 . In this way the scraper  30  is reliably attached to the nut  20  and travel onwards along with the nut  20  without slipping. The present invention further derives a preferable relationship between the pitch P and the clearance δ as: P≦720°·(δ/L), wherein L is the lead of the screw bolt  10 . 
     FIG. 6  shows a second embodiment of the present invention. As shown in  FIG. 6 , tooth portions  41  and hook portions  42  are separately fabricated before assembling to form a unit scraper  40 . Each tooth portion  41  has a tooth  411  to mesh the thread of the screw bolt  10  (not shown), and coupling slots  412  at the outer side to be engaged with the corresponding hook portion  42 . The hook portion  42  is provided with a plurality of pawls  421  and keys  422  respectively on its outer and inner edges so as to couple with the coupling slots  412 . With such a versatile design this two-part separately fabricated scraper is applicable universally for various sized ball screw unit by only selecting a suitable part of tooth portions  41  to meet a ball screw unit having a compatible thread pitch and ball size. 
   In a third embodiment of the present invention show in  FIG. 7 , a scraper  50  is also provided with tooth portions  51  and hook portions  52  respectively at its inner and outer sides. A slit  53  is formed at the circumference of the scraper  50  by cutting a small part open thereof. When assembling, the operator may pull apart the two sides of the slit  53  a little bit and squeeze the scraper  50  into the spiral groove of a desired ball screw unit. In this manner the pawls at the outer edge with being about to be squeezed are exerted by a small compressive clipping force of slit  53  which in turn serves to shrink the inner diameter of the scraper  50  and further enhance the close attachment of the scraper  50  to the screw bolt  10  thereby upgrading the applicability and dust preventing effect. 
   Various shaped slits provided with the scraper are shown in  FIG. 8 , and the various shaped pawls provided with the scraper are shown in  FIG. 9 . As shown in  FIG. 8 , the slits  53 A, B, C are formed between the adjacent pawls of the hook portion  52  for providing the positioning effect for the scraper in different situations. As shown in  FIG. 9 , the head surface of the pawl  321  of the hook portion  32  is formed into a slanted semi-circular plane as in A, a slanted arcuate curved surface as in B, or a cone shaped plane as in C. 
   Besides, the tooth portions of the scraper are made of an oil immersed rubber material so as to lubricate properly the ball screw unit when it is in use with this scraper. 
   Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustration of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than the examples given. 
   It should be emphasized that the present invention is a high level technical creation and by no means, simply utilizes conventional technology or know ledge known prior to the application for patent or can easily made by the persons skilled in the arts. Prior to the application for patent, the invention has neither been published or put to public use, nor displayed in an exhibition therefore the present invention is entitled for a patent.