Abstract:
A honing machine for super finishing workpieces, e.g. by honing using a tool spindle ( 7 ), can be rotatably driven and can receive a tool. A motor rotates the tool spindle, the tool spindle ( 12 ) being arranged on a carriage ( 12 ), which can be displaced on a machine frame ( 16 ), by means of a drive device, in the direction of the rotational axis of the tool spindle. The drive device consists of a flat primary part ( 13 ) and a secondary part ( 17 ) of an electric linear motor ( 18 ), the secondary part being linearly displaceable along the primary part. One ( 13 ) of the components primary part/secondary part ( 13, 17 ) of the linear motor ( 18 ) is disposed on the machine frame ( 16 ), and the other ( 17 ) on the carriage ( 12 ).

Description:
This application is the national stage of PCT/EP03/00379 filed on Jan. 16, 2003 and also claims Paris Convention priority of DE 102 25 514.8 filed on Jun. 10, 2002. 
   BACKGROUND OF THE INVENTION 
   The invention concerns a machine for superfinishing workpieces by honing or precision grinding according to the independent claim. 
   SUMMARY OF THE INVENTION 
   Honing machines are used for the above-mentioned tasks. A honing tool is provided with an appropriate coating (e.g. of diamond or corundum) and is introduced into a bore while simultaneously being turned and reciprocated to process the inner surface of the bore. To take into account the wear of the honing tools, these are i.a. designed to have honing strips provided with a honing layer which can be adjusted in a radial direction by means of a widening bar which rotates along with the honing tool but can be displaced therein in an axial direction. 
   Machines can moreover be used, with which a tool must be mounted to the device in a direction which corresponds to the axial direction of the rotational motion of the machine. These may be honing tools (e.g. for so-called “mandrel honing”) and also lapping tools. They could also be precision grinding tools to subject e.g. pre-ground valve seat surfaces to final superfinishing, wherein only a few micrometers must be removed in an exactly defined manner thereby simultaneously improving the surface. 
   The lifting motion of the carriage supporting the honing spindle of honing machines has generally been conventionally effected via a hydraulic drive, while the rotational motion of the honing spindle and thereby also that of the honing tool disposed therein, is effected by a common electromotor. The simultaneous rotational and lifting motions of the honing tool during honing produces a cross-grinding pattern on the surface to be processed, which is typical for this type of treatment, this pattern being important for the bearing and lubricating properties of the processed workpiece and also for the fitting accuracy of further components (e.g. pistons). For processing smaller bores having a diameter of only a few millimeters and simultaneous increase of the rotational speed of the honing tool to reduce the processing time, the stroke speed must be correspondingly increased. The hydraulic drives used to provide the stroke motion are thereby limited with regard to speed and reversibility of the system during operation. This is particularly true when the strokes are short as is the case when the processing depth of the bores is in the range of a few millimeters. 
   It is the underlying purpose of the invention to eliminate these disadvantages. In particular, means should be provided for the stroke motion which permit higher stroke speeds while thereby maintaining high reversal accuracy to ensure that small and short bores can also be processed more exactly and rapidly at higher honing tool rotational speeds. This object also addresses the problem of exactly realizing very short delivery paths for the carriage supporting the honing spindle, such as those which occur e.g. during precision grinding of valve seat surfaces. Moreover, the entire construction should be simplified by reducing the number of moving parts thereby also reducing costs. 
   This object is achieved in accordance with the invention with the elements recited in the claims. 
   A so-called linear motor is used which permits higher lifting and delivery speeds, has considerably less components, can be reversed with more precision and allows short stroke paths at high speed. 
   The use as honing machine, i.e. use of a honing tool with radially adjustable honing strips, is facilitated in that the widening bar for radial adjustment of the honing strips, which is actuated by a connecting rod disposed in the honing machine, can also be actuated in a more simplified manner using a servomotor which, in turn, may preferably be flanged coaxially to the coupling housing and disposed as a linear extension to the spindle housing. The connecting rod can also be preferably adjusted via a further linear drive. The invention may then also be used to perform a rapid and precise, minimum, exactly defined, stroke motion of a precision grinding tool, e.g. for processing a valve seat. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Embodiments of the invention are described in more detail below with reference to the enclosed drawings. 
       FIG. 1  shows a schematic view of a honing machine which is designed in accordance with an embodiment of the invention; 
       FIG. 2  shows a honing spindle housing  8  of the honing spindle  7 , the carriage  12  and the sliding rails  14  as well as the carrier  15  carrying the sliding rails  14  and disposed on the machine frame  16 , the view being tilted by 90° with respect to  FIG. 1 ; 
       FIG. 3  shows a view in the direction of the arrows III—III of  FIG. 2 ; 
       FIG. 4  shows a section through the spindle housing  8 ; 
       FIG. 5  shows a section through the coupling housing  51  which is flanged to the spindle housing  8 ; 
       FIG. 6  shows a section through the coupling housing  51  of a second embodiment of the invention which is suited, in particular, for small stroke motion in an axial direction; 
       FIG. 7  shows a view in the direction of arrows VII—VII of  FIG. 6 ; 
       FIG. 8  shows a schematic representation of a workpiece  301  and an associated tool  300  which can be used with the embodiment of  FIGS. 6 and 7 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a honing machine. A workpiece  2  is clamped on a processing platform  1  for honing a bore  3  thereof. The honing tool  4  which is received in a cone  6  at the end of the honing spindle  7  is lifted and lowered with the honing spindle  7  thereby providing the conventional stroke motion of the honing process, as is part of the honing method. The axial displacement of the honing spindle  7  serves to generate this stroke motion. The honing tool  4  has radially adjustable honing strips  5 . The honing spindle  7  is driven by an electromotor  9  which is integrated in the spindle housing  8 . A coupling housing  51  is flanged to the upper end (in  FIG. 1 ) of the spindle housing  8 , and a servomotor  10  is coaxially flanged to the coupling housing  51 . The servomotor  10  provides axial displacement of a widening bar  11  which is disposed in the honing tool  4  and passes through the rotating honing spindle  7  for radial adjustment of the honing strips  5 . 
   The spindle housing  8  is disposed on a carriage  12  in which the primary part  13  of a linear motor  18  is integrated. The primary part  13  forms a linear motor  18  together with the secondary part  17  which is integrated in the vertically extending carrier  15  (see  FIG. 3 ). This linear motor  18  effects the lifting motion of the spindle housing  8 . The carrier  15  is mounted to the machine frame  16 . The carriage  12  with Integrated primary part  13  can be lifted and lowered on the sliding rails  14 , which, In turn, are fixed to the carrier  15 . The primary part  13  is the moving part and the secondary part  17  is the stationary part of the linear motor. 
   Use of a linear motor whose moving part carries the honing spindle and thereby performs the stroke motion with the required speed and reversal accuracy is of primary importance to the invention. To process the bore  3 , the spindle housing  8 , including honing spindle  7  and honing tool  4  received therein, is lowered to such an extent that the honing strips  5  penetrate into the bore  3 . The honing spindle  8  is simultaneously reciprocated (lifted and lowered) and turned. These two motions are matched to generate the “cross-grinding pattern”, which is typical for honing, on the workpiece surface at an angle of e.g. 10° to 50°. For smaller diameters of the bore to be processed and high rotational speeds, this pattern requires a relatively fast lifting and lowering of the honing spindle  8 , which is ensured by the linear motor  18 . An inventive honing machine with e.g. a stroke of 80 mm can have a stroke speed of 50 m/min with a reversal accuracy of ≦0.05 mm (reversal is the change of motion from one direction to the opposite direction). With a stroke of 20 mm, it can have a stroke speed of 25 m/min with a reversal accuracy of ≦0.04 mm. 
   As is shown in  FIG. 3 , the primary part  13  of the linear motor  18  is mounted to the carrier  15  via screws  19  and the sliding rails  14  are mounted to the carrier  15  via screws  20 . The profile of the sliding rails  14  corresponds to the profile of the sliding elements  21 , which are mounted to the carriage  12  via screws  22 . The primary part  13  of the linear motor  18  is mounted in the carriage  12  via screws  23 . 
   The person skilled in the art is familiar with linear motor construction and an exact description is therefore unnecessary herein. Linear motors can be obtained from various manufacturers. They are driving elements which are developed from a normal rotary current electromotor by “cutting open” the stator and unfolding it into a plane. The rotor is also planar such that it moves along the linear extension of the stator in correspondence with the alternating electromagnetic field which propagates along the windings of the stator. In the present case, the primary part  13  corresponds to the stator, the secondary part  17  to the rotor of an electromotor. It is a synchronous device and is designed as a long stator motor. The speed is controlled via frequency variation in a frequency converter of an associated control. A programmable control (not shown) permits adjustment of corresponding speed as stated above. 
   A carrier frame  171  is mounted on the carrier  15  using screws  170 , only one of which is visible, and a measurement transducer  173  is disposed on the carrier frame  171  via screws  172 . It contains conventional measurement markings (not shown) which generate measuring signals in sensors (not shown) disposed on the carriage during motion of the carriage  12  perpendicular to the plane of the drawing of  FIG. 3 , the measuring signals showing the instantaneous position of the carriage  12  and transmitting it to the control (not shown).  174  designates a cover plate. 
   The structure of the spindle housing  8  is shown in  FIG. 4 . The electromotor  9  is integrated in the spindle housing  8 . It causes rotation of the honing spindle and consists of a stator  25  with windings  25 ′ and rotor  26 . The stator  25  is pressed into a sleeve  37  which is screwed to the end plates  33 ,  34  using screws  36  (only shown at  34 ). The rotor  26  is pressed onto the outside of the honing spindle  7 . The stator  25  is supplied with current via the connections  27 . The motor  26  is a permanent magnet. The spindle housing  8  is screwed to the carriage  12  using screws  30 . The honing spindle  7  is supported in the spindle housing  8  via bearings  31  or  32  in front and rear end plates  33  and  34 . The end plates  33  or  34  are screwed to the spindle housing  8  using screws  35 . The sleeve  37  has a spiral cooling channel  38  which is supplied with coolant via the coolant delivery line  39 . The coolant discharge is not shown: It is disposed on the opposite side. 
   The radial coupling housing  51  which joins the connecting plate  34  on the left-hand side, and the servomotor  10  which adjusts the widening bar  11  of the honing strips  5  of the honing tool  4  are shown in  FIGS. 4 and 5 . 
   The honing spindle  7  has a continuous bore  40  in which the connecting rod  110  is disposed to be displaceable in an axial direction. The lower end of the connecting rod  110  has a bore  112  with inner thread into which the widening bar  11  is rigidly screwed, such that the connecting rod  110  and the widening bar  11  form a unit and can be commonly displaced in the longitudinal direction (axial direction) of the axis of rotation. The honing strips  5  are thereby radially displaced towards the outside. Honing tools  4  of this type are known In the art. During operation, the honing strips are radially pulled inward through springs and have inclined adjustment surfaces on their inner sides which cooperate with correspondingly inclined adjustment surfaces at the end of the widening bar  11  such that, when the widening bar  11  is axially displaced, the honing strips  5  are radially adjusted (spreading mechanism). 
   The connecting rod  110  and the widening bar  11  rotate together with the honing spindle  7  but can also be axially displaced therein (in the longitudinal direction) as mentioned above. This is realized in that the connecting rod  110  is penetrated by a pin  46  whose ends are guided in opposite grooves  46 ′ in the honing spindle  7 . The bore  40  in the honing spindle  7  has a shoulder  43  onto which a ring  41  is urged via a spring  45  which is supported with its other end on the pin  46 . At rest, the connecting rod  110  is forced by the spring  45  in its outermost upper position shown in  FIG. 4 . The connecting rod  110  may then be downwardly displaced against the force of the spring  45 . 
   The plunger  47  is a continuation of a coupling piece  49  into the axial recess  49 ′ of which the driven shaft  50  of the servo motor  10  projects. Coupling in the rotational direction with is realized by a tongue/groove connection formed by a groove  151  and wedge (“spring”)  152 . 
   The coupling housing  51  is screwed to the front end plate  34  of the spindle housing  8 . The screws are not shown. A sleeve  52  is Inserted into the coupling housing  51 . The sleeve  52  can be axially displaced in the coupling housing  51 , since a block  160 , which is screwed into the sleeve  52  and radially projects past it, projects into a groove  161  in the sleeve  53  and is guided therein. The sleeve  52  can be displaced relative to the coupling housing  51  through a stroke H. The upper end of the connecting rod  110  is rotatably disposed in the sleeve  52  using bearings  165 . The inner shells of the bearings  165  are rigidly connected to the connecting rod. A lid  166  is screwed to the connecting rod  110  to fix the bearing  165 . 
   The sleeve  52  also receives an adjusting sleeve  53  which rotates therewith and can be displaced and adjusted in a longitudinal direction. This connection is also realized through a tongue and groove connection which is formed by the wedge  54  and the groove  55 . The adjustment sleeve  53  is penetrated by a bore which has an Inner thread  56 . An outer thread  56 ′ of the plunger  47  engages therein. The adjustment sleeve  53  is secured in the sleeve  52  through a lid  167  which is screwed to the sleeve  52 . When the servomotor  10  and thereby also its driven shaft  50  rotate, the coupling piece  49  is also rotated due to the tongue and groove connection  151 ,  152 . Due to engagement of the threads  56 ,  56 ′, the sleeve  52  is displaced in an axial direction and the connecting rod  110  together with the widening bar  11  are displaced in a downward direction against the force of the spring  45 , thereby effecting radial adjustment of the honing strips  5  within the honing tool  4  as mentioned above. 
     170  is a sensor having an end switch which transmits the shown end position consisting of sleeve  52 , block  160 , bearing  165  and connecting rod  110 , and a corresponding measured signal to the control (not shown). 
   A further embodiment is described below with reference to  FIGS. 6 and 7 . The servomotor  10  is replaced by a linear motor and supplies a superfinishing tool  30  which is disposed at the end of the bar  306 . It is connected to the connecting rod  120 . The connecting rod  120  is rotatably disposed in the adjustment sleeve  253  using bearings  265 , wherein the lid  266  is screwed into the adjustment sleeve  253  such that the connecting rod  120  can be rotated in the adjustment sleeve  253  but not be displaced in an axial direction thereto. The runner, i.e. the movable primary part  201  of a further linear motor  200  is rigidly connected to the adjusting sleeve  253 . The linear motor  200  also has a secondary part (not shown). It is a construction type of a linear motor, wherein the runner is round and the inner space of the stator is also round. Such construction types of linear motors are also known per se. It is clear that the use of a linear motor requires much less components, including those for the adjustment motion of the connecting rod  110  and of the bar  306  connected thereto. Moreover, these components are subjected to much less wear.  FIG. 7  shows suspension of this further linear motor  200  using a clamping plate  210 . 
   The embodiment with axial delivery of the bar  306  in accordance with  FIGS. 6 and 7  addresses a processing task which is explained by means of  FIG. 8 . The tool is a conical precision grinding body  300  which serves for processing a valve seat surface  305 . The valve seat surface  305  must thereby be removed by a defined amount, e.g. a few hundreths of a millimeter, which is calculated e.g. using a sensor. The shape and surface must be simultaneously improved. The conical precision grinding body  300  is disposed on the bar  306  which has a threaded pin  307  at its end which is connected to the end of the connecting rod  120 . In this manner, minimum stroke paths can be realized by means of the servomotor  10  or the further linear motor  200 . This may be effected either with one stroke motion or several small stroke motions which are intermittently applied, e.g. for sparking out after only relatively few rotations or for rinsing with coolant after each stroke.