Abstract:
A fixed base router has a base supporting an upright wall. A motor based driver assembly is received in a cylindrical interior space delimited by the wall and movable along a spiral path. A read-out system includes a position sensor that detects and applies the displacement of the driver assembly along the spiral path to a processor based circuit, which in turn generates a signal indicating the displacement and a display device showing up the displacement for visual inspection. The read-out system allows for precise positioning the driver assembly and thus setting a cutting depth of a tool bit carried on and driven by the driver assembly so that adjustment of positioning of the tool bit is made simple, readable and precise.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a router, and more particularly, to a fixed base router which comprises a digital read-out system. 
   2. The Related Arts 
   Router is a power tool used to cut a workpiece for forming grooves, edges and a variety of shapes of the workpiece. A router that, in a cutting operation, maintains a fixed position of a tool bit thereof with respect to a workpiece is generally referred to as a “fixed base router”. The fixed base router allows manual movement of the tool bit toward and/or away from the workpiece in accordance with the required depth of cutting. However, obtaining a desired cutting depth is a time consuming task for it generally involves a trial and error process where a user cuts a sample of stock, measures the resulting cutting depth, and then attempts to make the appropriate corrective adjustment. This process is generally repeated several times before the desired cutting depth is obtained. Thus, the adjustment is in fact cumbersome and time-consuming. 
   The present invention is made to overcome the inefficiency of trial-and-error process used to obtain a desired cutting depth in a conventional router. 
   SUMMARY OF THE INVENTION 
   The primary object of the present invention is to provide a fixed base router comprising a read-out system to precisely display the cutting depth of a tool bit. 
   In accordance with the present invention, a fixed base router is provided, comprising a base supporting an upright wall. A motor based driver assembly is received in a cylindrical interior space delimited by the wall and is movable along a spiral path. A read-out system comprises a position sensor that detects and applies the displacement of the driver assembly along the spiral path to a processor based circuit, which in turn generates a signal indicating the displacement and a display device showing up the displacement for visual inspection. 
   The router in accordance with the present invention comprises the read-out system that allows for precise positioning the driver assembly and thus setting a cutting depth of a tool bit carried on and driven by the driver assembly so that adjustment of positioning of the tool bit is made simple, readable and precise. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention will be apparent to those skilled in the art by reading the following description of preferred embodiments thereof, with reference to the attached drawings, wherein: 
       FIG. 1  is a front view of a router constructed in accordance with a preferred embodiment of the present invention; 
       FIG. 2  is a back view of the router illustrated in  FIG. 1 ; 
       FIG. 3  is a front view of a driver assembly of the router in accordance with the present invention; 
       FIG. 4  is a front view, partly broken, of a base assembly of the router in accordance with the present invention; 
       FIG. 5  is a partly cross-section view taken along the line V-V of  FIG. 1 ; 
       FIG. 6  is a cross-section view taken along the line VI-VI of  FIG. 1 ; 
       FIG. 7  is a perspective view of an encoding disk consisting a position sensor of the router in accordance with the present invention; 
       FIG. 8  is a perspective view of another encoding disk consisting the position sensor of the router in accordance with the present invention; 
       FIG. 9  is a perspective view of a further encoding disk consisting the position sensor of the router in accordance with the present invention; 
       FIG. 10  is a front view, partly broken, of a router constructed in accordance with another embodiment of the present invention; and 
       FIG. 11  is a cross-section view taken along the line XI-XI of  FIG. 10 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to the drawings and in particular to  FIGS. 1 and 2 , a fixed base router is illustrated as an example for describing the present invention. The router comprises a base assembly  1 , a driver assembly  2  that is moveably mounted on the base assembly  1  and carrying therein a power driver device, such as a drive motor  23  (shown in dashed lines in  FIG. 1 ) that powers a tool bit  22  for machining a workpiece (not shown), and a read-out system  3  that is supported on the base assembly  1 . Alternatively, the read-out system  3  may be mounted on the driver assembly  2 . 
   The base assembly  1  comprises a generally planar support plate  11  in which an opening or a hole  110  is defined for the selective extension of the tool bit  22  of the driver assembly  2 . A surrounding wall  12  extends from the support plate  11  in an axial direction toward the driver assembly  2 , defining a hollow, cylindrical interior (not labeled) in which the driver assembly  2  is movably and rotatably received. Preferably, two handles  13  are mounted on the wall  12 . The surrounding wall  12  is split with an elongate opening  130  formed between two opposed ends and two brackets  14  and  15  each having a tapped hole (not shown) are respectively formed on the opposed ends of the wall  12  adjacent to the opening  130 . A bolt  16  engages with and extends through both tapped holes of the brackets  14 ,  15  to releasably secure the wall  12  to the driver assembly  2  so as to maintain the position of the driver assembly  2  relative to the base assembly  1 . 
   The driver assembly  2  comprises a generally cylindrical housing  21  in which the drive motor  23  is fixed. The drive motor  23  has a spindle (not shown) to which the tool bit  22  is mounted. The drive motor  23  selectively drives rotation of the tool bit  22  to work on the workpiece. The cylindrical housing  21  is movably received in the interior space of the surrounding wall  12  to selectively move the motor  23  and the tool bit  22  with respect to the base assembly  1 . 
   The read-out system  3  comprises an electrical circuit comprising a position sensor (indicated at  31   a  in  FIG. 5 ;  31   b  in  FIG. 10 ), a processing device (not shown), a display device  32  that comprises a liquid crystal display (LCD) in the embodiment illustrated, but may be other known displaying devices, such as a light-emitting diode (LED) based display, a reset switch  33  for resetting data displayed on the display device  32  to zero, and a mode switch  35  for switching between for example an English or Metric units read-out. The read-out system  3  is powered by for example a built-in power source, which may comprise one or more batteries, either primary or secondary, or an external AC power from an electrical main through an AC/DC power adaptor circuit. 
   As be best shown in  FIG. 3 , an outer circumference of the cylindrical housing  21  is formed with a plurality of pins  211  that extends in a radial direction. A spiral groove  121  is provided in an inner surface of the surrounding wall  12  and slidably receiving the pins  211  of the housing  21  of the driver assembly  2  to guide spiral movement of the driver assembly  2  with respect to the base assembly  1 . The cooperation between the pins  211  of the driver assembly  2  and the spiral groove  121  of the wall  12  of the base assembly  1  effects a camming action for conversion of rotation of the driver assembly  2  with respect to the wall  12  of the base assembly  1  into linear movement of the driver assembly  2  in the axial direction of the base assembly  1 . 
   Apparently, other modifications and alternatives that enable the spiral movement of the driver assembly  2  with respect to the surrounding wall  12  of the base assembly  1  and that are apparent to those skilled in the art can be employed to effect the conversion between rotation and linear axial movement of the driver assembly  2 . For example, the pins can be formed on the inner surface of the wall  12  of the base assembly  1  slidably received in spiral groove defined in the outer circumference of the housing  21  of the driver assembly  2 . This provides the same camming action between the driver assembly  2  and the base assembly  1 . 
   Another modification can be made as being easily anticipated by those having ordinary skills by replacing the pin  211  and the spiral groove  121  with mated external and internal threads or screws formed on the outer circumference of the cylindrical housing  21  of the driver assembly  2  and the inner surface of the surrounding wall  12  of the base assembly  1 . The mated screw threads between the driver assembly  2  and the base assembly  1  effect a screw-based transmission that enables the spiral movement of the driver assembly  2  with respect to the base assembly  1 , or conversion of the rotation of the driver assembly  2  into linear axial movement. 
   Also, a plurality of axial grooves  212  is defined in the outer circumference of the housing  21  and extends in the axial direction. 
   As shown in  FIG. 4 , a cone gear  17  is concentrically and rotatably mounted to the surrounding wall  12  of the base assembly  1  and provides a cylindrical bore (not labeled) sufficient to receive the driver assembly  2  therethrough. The cone gear  17  forms a plurality of protrusions  171  that is inward extended to respectively engage with the axial grooves  212  defined in the housing  21  of the driver assembly  2  so as to rotatably fix the cone gear  17  to the housing  21  of the driver assembly  2 . In other words, the cone gear  17  rotates in unison with the driver assembly  2 . 
   Also referring to  FIGS. 5 and 6 , the position sensor  31   a  of the read-out system  3  comprises an encoding disk  33   a  that is in driving coupling with the housing  21  of the driver assembly  2 , which will be further described, and a counter  32   a  fixed to the surrounding wall  12  of the base assembly  1 . The position sensor  31   a  as illustrated in the embodiment of  FIGS. 5 and 6  serve to detect rotation (angular displacement) of the driver assembly  2  when the driver assembly  2  carries out the spiral movement with respect to the surrounding wall  12  of the base assembly  1 . In this respect, a transmission system is provided between the housing  21  of the driver assembly  2  and the encoding disk  33   a , which comprises the cone gear  17  and a gear train embodied in the form of toothed shafts  18 ,  19 . The first shaft  18  forms a pinion  181  mating the cone gear  17  and a gear  182 . The second shaft  19  forms a gear  191  mating the gear  182  of the first shaft  18  and is rotatably fixed to the encoding disk  33   a  by having a shaped end fit into a corresponding shaped bore  331   a  defined in the encoding disk  33   a . Thus, the rotation of the housing  21  of the driver assembly  2  is transmitted through the cone gear  17  and the first and second shafts  18 ,  19  to the encoding disk  33   a  that is rotatable in unison with the second shaft  19 . 
   The base assembly  1  is provided with a chamber  121  in which the gear shafts  18 ,  19  and gears  182 ,  191  and the pinion  181 , as well as the encoding disk  33   a  are accommodated. 
   In an aspect of the present invention, the counter  32   a  comprises an optical switch which comprises a light transmitter  321  and a light receiver  322 . Referring to  FIG. 7 , the encoding disk  33   a  comprises a disc plate  334  in which the bore  331   a  is formed for receiving the second shaft  19  and a cylindrical wall  335  extending from the disc plate  334 . A plurality of through holes or notches  332   a  is defined in the cylindrical wall  335  and is equally spaced along a circumference of the wall  335 . The light transmitter  321  and the light receiver  322  are respectively located on opposite sides of the wall  335  whereby rotation of the encoding disk  33   a  causes the notches  332   a  to sequentially pass between the light transmitter  321  and the light receiver  322 . Consequently, the light receiver  322  repeatedly receives a light emitted from the light transmitter and pulse-like signal is induced. Thus, an angular displacement of the encoding disk  33   a  can be calculated based on the counts of the pulses indicating that the light receiver  322  detects light from the light transmitter  321 . 
   When the driver assembly  2  is manually rotated to effect adjustment of position thereof with respect to the base assembly  1 , an angular displacement induced by the rotation of the driver assembly  2  is transmitted through the cone gear  17  and the shafts  18 ,  19  to the encoding disk  33   a . Based on the angular displacement of the encoding disk  33   a  determined by counter  32   a , the angular displacement of the driver assembly  2  can be determined because the ratio of angular displacement between the driver assembly  2  and the encoding disk  33   a  is set by the geometrical data of the cone gear  17 , the gears and pinions of the shafts  18 ,  19  and the spacing of the notches  332   a  of the encoding disk  33   a . The angular displacement of the driver assembly  2  is then converted into linear axial displacement based on the geometric data of the pins  211  and the spiral groove  121 , or those of mated screws between the driver assembly  2  and the base assembly  1 . All these are processed by the processing device that receives data from the counter  331 , calculates the movement and generates a position signal that is fed to and displayed on the display device  32 . 
   In another aspect of the present invention, the encoding disk, which is designated with reference numeral  34   a  for distinction, is made transparent and comprises a plurality of opacity sections  341   a  equally-spaced around the wall of the encoding disk  34   a , as shown  FIG. 8 . The opacity sections  341   a  serves to block the transmission of the light from the light transmitter to the light receives in a regular manner whereby counts of detection of light by the light receiver can be based to determine the angular displacement of the driver assembly  2 . In a further aspect, the counter  32   a  is embodied as a Hall sensor, and corresponding thereto, the encoding plate, which is designated with reference numeral  35   a , comprises a plurality of magnets  351   a  attached to the wall of the encoding disk  35   a  in a circumferentially equally-spaced manner, as shown in  FIG. 9 . 
   Referring to  FIGS. 10 and 11 , a router constructed in accordance with another embodiment of the present invention is shown. In the router, a position sensor that is designated at  31   b  is provided to detect linear axial displacement of the driver assembly  2  when the driver assembly  2  is subject to spiral movement with respect to the base assembly  1 . The router comprises an axially-extending V-shaped channel  122  formed in the inner circumference of the surrounding wall  12  of the base assembly  1 . The position sensor  31   b  comprises a capacitance transducer comprising a fixed sensor rail  32   b  fixedly mounted in the V-shaped channel  122 , and a movable sensor element  33   b  moveably received in the V-shaped channel  122  adjacent to the fixed sensor rail  32   b  and biased by a biasing member  20  against the driver assembly  2 . (For example, the sensor element  33   b  has a projection (not labeled) put in abutting engagement with the cylindrical housing  21  of the driver assembly  2  by the biasing force of the biasing member  20 .) The sensor element  33   b  is movable with respect to the V-shaped channel  122  and thus the wall  12  of the base assembly  1  in a linear and axial movable manner. 
   When the driver assembly  2  is manually operated to take a spiral movement for moving away from or toward the support plate  11  of the base assembly  1 , the movable sensor element  33   b , under the biasing force of the basing member  20 , is moved with the driver assembly  2 . For example, when the driver assembly  2  is moved upward, the sensor element  33   b  is biased upward by the biasing member  20  (with the biasing member  20  extending) to follow the driver assembly  2  and when the driver assembly  2  is moved downward, the sensor element  33   b  is driven downward by the driver assembly  2  against the biasing member  20  (so that the biasing member  20  is compressed). The relative movement of the movable sensor element  33   b  with respect to the fixed sensor rail  32   b  is thus detected and signal associated with the relative movement is transmitted to the processing device whereby the processing device converts the signal, which represents data of movement, into a position signal fed to and displayed on the display device  32 . 
   To carry out adjustment of cutting depth in a workpiece, an operator manipulates the power switch  34  of the read-out system  3 , releases the bolt  16  and manually rotates the driver assembly  2  to make the driver assembly  2  moving in a spiral fashion with respect to the base assembly  1 . When the tool bit  22  that is carried by the driver assembly  2  gets into contact with the workpiece, the operator manipulates the reset switch  33  to reset the display device  32  to zero. Thereafter, the router is actuated to have the driver assembly  2  moving the tool bit  22  through the extending the hole  110  defined in the support plate  11  of the base assembly  1 . The position sensor detects angular displacement or axial displacement of the spiral movement of the driver assembly  2  with respect to the wall  12  of the base assembly  1 , and data associated with the detected displacement is transmitted to the processing device. The processing device converts the detected displacements into a position signal that is fed to and displayed on the display device  32  for visual inspection of the cutting depth set by the operator. When the desired depth is achieved, the operator secures the bolt  16  to maintain the position of the driver assembly  2  with respect to the base assembly  1 . 
   Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.