Abstract:
An automated clamping system for securing a work piece to the table of a machine tool. The clamping system automatically retracts away from the work piece as the material manipulating device moves into the area of each clamp. This allows manipulation of the work piece without stopping to move the clamp to a new location so that the clamp does not interfere with the metal manipulating device. A typical embodiment is the use of the system on a milling machine. The clamping system could be used with milling machines (both manual and computer controlled), routers, water jet cutters, laser cutters, flame cutters, and many other types of cutting machines.

Description:
CROSS REFERENCES 
       [0001]    This application claims the priority of Provisional Application USPTO No. 61/126,758 filed on May 6, 2008 under 35 U.S.C. 111b. 
     
    
     STATEMENT REGARDING FEDERAL SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    This application is not the result of a federally sponsored research or development effort. 
       PARTIES INVOLVED IN JOINT RESEARCH AGREEMENTS 
       [0003]    The inventor is not involved in any joint research agreements or obligations to assign the invention described herein. 
       REFERENCE TO PROGRAM LISTING 
       [0004]    A program listing is provided in appendix A for use on a Tri-Research PLC. 
       FIELD OF THE INVENTION 
       [0005]    The invention generally relates to metal manipulating devices used to cut work pieces that are typically held in place by some form of clamping. A typical embodiment would be for use on the table of a milling machine. The invention automatically removes the clamp from the cutting area as the cutting tool moves into the area of each clamp. This eliminates the need to stop the cutting process to move the clamp manually. 
       BACKGROUND OF INVENTION 
       [0006]    This application is to be filed under 35 U.S.C. 111(a) and claims priority under 35 U.S.C. 119(e) to provisional application USPTO No. 61/126,758 filed on May 6, 2008 under 35 U.S.C. 111b. 
         [0007]    A new machine tool clamp system is specially adapted to prevent the tool bit from contacting the clamp while allowing the tool access the entirety of all sides and top of the work piece. 
         [0008]    Machine tools, including various types of mills and routers, allow operators to manipulate metal and other materials. Most machine tool systems make use of manual clamps to secure a work piece in a fixed position relative to the tool. These clamps are typically secured with bolts that are adjusted manually in order to apply or release a clamping force with respect to the work piece. 
         [0009]    In other instances the work piece is held in a vise which grips two opposite sides. This method does not allow the manipulation of the work piece on the two sides. 
         [0010]    Another method that is commonly used, is to bolt the work piece to a piece of scrap, this allows the manipulation of all edges, but requires additional “mounting” holes in the work piece. An additionally problem with this approach is that the holes required in the part need to allow for clearance around the bolts. This clearance provides some uncertainty as to the location of “mounting” holes relative to the finished part. 
         [0011]    Additionally, most CNC machining centers provide for additional digital outputs which can be controlled by the machining program. Using this method has its own difficulties. First, the CNC programmer must consider the location of each clamp while writing the machining program and the operator doing the setup must properly locate the clamps. Second, the CNC machining center (or milling machine) must provide the digital outputs required for all the clamps. Many CNC machining centers (and milling machines) do not provide enough. Third, the digital outputs must be provided; in the case of manual milling machines such functionality is typically not available. 
         [0012]    Yet another problem with existing clamping mechanisms is the need to provide hydraulic clamping systems to provide the required clamping force during some work piece manipulations. Typically, manufacturers have easy cost effective compressed air available. This compressed air is used to blow chips and debris from the manipulating area during clean up or “on machine” inspection. The use of a pneumatically actuated clamp is desirable in situations where the manufacturer doesn&#39;t yet have the need for hydraulics. 
       SUMMARY OF THE INVENTION 
       [0013]    The invention provides an automated clamping system; this clamping system provides several advantages over conventional clamping systems. The invention includes a clamp which increases the clamping force as the foot comes to rest on the work piece and increases the travel as the foot retracts from the work piece, provides for common pneumatic (or other, electric, hydraulic) clamping methods, provides for automatic retraction of the clamping foot allowing clearance in the material working area, and provides for a method of clamping work pieces using the device. 
         [0014]    One aspect of the design is the ability to retract from the metal working area as the cutting tool moves into the area of the clamp. This retraction allows the metal working device to continue to function without being obstructed by the clamp. Additionally, the design allows for locating debris sensitive components (i.e. air cylinder) out of the metal working area this improves the life of the sensitive component. 
         [0015]    The clamping system allows for greater production time as the machine does not need to be stopped while the clamp is repositioned. A typical manual clamp will not retract to clear the cutting tool and so as the cutting tool approaches the operator must stop the cutter to move the clamp. 
         [0016]    Another advantage is the ease of clamping work piece to the table during repetitive machining operations where several work pieces are manipulated sequentially. Each finished part is released by the operator pressing each clamp control button on the control panel, then simply placing the next work piece into the clamps and switching the clamp control switch to the clamp position. 
         [0017]    The work piece in this design need not be preprocessed to allow for a method of clamping during the machining process. No “mounting” holes are required, no finished sides of the work piece need be existing (as in the case of clamping) and the work piece is not manipulated to allow access to any of the sides for additional work piece operations. 
         [0018]    The control system for the clamp provides for the retraction (unclamping) and later extension (re-clamping) of the work piece as the machining tool moves into and away from the clamp area. The advantages of this system include; 1) when used on a programmable material manipulating machine, the program used for manipulation need not consider the location of the clamps; 2) when setting up the clamps accurate location is not required relative to the program of the material manipulating machine (milling machine program); 3) Since the device does not require interfacing with the program used to manipulate the work piece the, the device can be used on a manual milling or routing machine. 
         [0019]    The control system “tracks” the table position by encoders located on the lead screw of the machining device. Note, the use of encoders and lead screws is dictated by the particular machine on which the clamp is used. Other devices such as linear encoders, rotary encoders with an attached drive system which provides rotation to the encoder as a function of table position will suffice. Additionally, any positioning system can be used these include but are not limited to resolvers, inductosyns, potentiometers (both linear and rotary) and Linear Voltage Transducers (LVDT). 
         [0020]    The clamping actuation is provided through a “push/pull” cable. This feature provides several advantages. First, the work area of the milling machine is reduced as large clamping generating devices (pneumatic, electric or hydraulic cylinders) are not located in the area. Instead the flexible push/pull cable provides for the mounting of these actuators to be located remotely. Secondly, actuators of this type may be prone to damage created by debris from cutting processes or cutting fluids. By locating these devices remotely they can be located such that this problem is eliminated. 
         [0021]    The method of use for the system can now be explained. Using a number of clamps typically four or more the operator locates the work piece and the clamps such that the finished part will be clamped by each of the clamps when the process is complete. Stated another way the clamps are to clamp on the area of the work piece in which the finished part will reside. Using a 3 way toggle button on the Control Panel (discussed more in the detailed description) established for each clamp the operator clamps the work piece. Now the operator moves the cutting tool into a position directly above each clamp. When the cutting tool is located above the clamp the operator presses the corresponding clamp button (the “SET” position of the toggle switch). Since the program for controlling the clamps is running when powered up the clamp retracts. This provides confirmation to the operator that the particular clamp position has been “taught” to the controller. This procedure is repeated for each clamp. The work piece may now be machined, as the cutting tool moves into each clamp area the corresponding clamp will retract providing clearance around the work piece. 
         [0022]    Although the use of four clamps is recommended for typical use the system is not limited by this particular requirement. The system can be used in addition to manual clamps. This would allow the machining of only the side or sides held by the automated clamp and may be advantageous when used with tooling for locating the work piece. Additionally, the number of clamps is not restricted to less than four. In cases where the work piece is very large additional clamps can be added without violating the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    FIG.  1 —an isometric view of the invention installed on a milling machine 
           [0024]    FIG.  2 —A cross sectional view of the actuator assembly 
           [0025]    FIG.  3 —An elevation view of the clamp mechanism 
           [0026]    FIG.  4 —A cross sectional view of the clamp mechanism showing the relative lengths of each linkages 
           [0027]    FIG.  5 —An isometric view of the controller, illustrating the programmable logic controller, power supply and valves 
           [0028]    FIG.  6 —A plan view of the interface panel 
           [0029]    FIG.  7 —A cross sectional view of an installed encoder assembly 
           [0030]    FIG.  8 —A plan view of a single clamp showing a typical retract area around a clamp 
           [0031]    FIG.  9 —An isometric of a single clamp—Suggested Drawing Figure 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    This description will illustrate the invention as used on a conventional milling machine. As implied above the invention can be used on several work piece manipulating devices these include numerically controlled milling machines, numerically controlled machining centers, routers, water jet and laser routers. 
         [0033]    The system is shown in  FIG. 1  and includes the controller item  100 , encoder assembly items  110 , multiple clamps items  140  and a control panel item  150 . In this drawing a typical milling machine item  130  along with a work piece item  120  are also shown. Though an implementation using a milling machine is shown the device could be easily modified for use on a router or other machine which mounts the cutting tool on actuators and the work piece is stationary. Additionally, the method of using the system is also provided. 
         [0034]    A side view of the clamp is shown in  FIG. 3 . This device consists of the linkages  5 ,  6  and  7 , the base  24 , the push/pull cable  15 , the push/pull cable jacket mount  14 , the spherical pivot assembly  22 , work rest  8 , and linkage pins  9 . This drawing shows the clamp in the clamped position, in this position the push/pull cable is pulling on the spherical pivot assembly  22  toward the push/pull cable jacket mount  14 . This pulling causes linkage  7  to rotate CCW and lift the end of linkage  6 , linkage  6  pivots into a position that causes linkage  5  to pivot CW into the work piece (not shown) that rests on the work rest  8 . 
         [0035]    The push/pull cable  15  of  FIG. 3  is actuated by a cylinder.  FIG. 2  shows a cross sectional view of the actuator assembly. The push/pull cable consists of a jacket  501  and an internal cable  502 . The cable inside the jacket  502  is free to slide. With a cable  502  that is longer than the jacket  501  (i.e. the ends of the cable protrude from the ends of the jacket), the cable  502  can be pulled and pushed from one end causing the other end to slide out and into the jacket  501 . This component is purchased and is readily available. Its advantages include removing the primary actuator  503  (i.e. air cylinder) from the area of the machining process, reducing the occupied space of the clamp and eliminating a need for mounting the primary actuator so that the actuating force can be transmitted to the mounting. The clamping force is transmitted through the jacket. 
         [0036]    The actuator assembly consists of a cylinder  503 , a cylinder mount tube  506 , a joint  505  and a jacket mount  507 . Additionally, the other end of the push/pull cable is also included. The joint  505  provides for mounting the cylinder rod to the end of the internal cable  502  of the push/pull cable assembly. This drawing shows the cylinder in the retract position this causes the internal cable of the push/pull assembly to extend from the external jacket  501 . The opposite end of the internal cable retracts and causes the clamp to grip the work piece. To release the work piece (or move away from the cutting tool) the cylinder extended causing the internal cable of the push/pull assembly to extend. This action causes the clamp to open clearing the cutting tool. 
         [0037]    The clamp structure includes a replaceable work piece rest. This rest is used for positioning the top surface of the work piece at the correct position. The rest is attached by screwing the rest onto a screw as shown in  FIG. 10 . Also understand that the rest can be adjusted in height by positioning the rest at any position along the screw. 
         [0038]    The control system tracks the position of the clamps and as each clamp moves into the area of the cutting tool the controller turns an output on causing the clamp to retract.  FIG. 8  shows a typical “clamp retract” area  600 . This rectangular area is established around each clamp during the set up process. 
         [0039]    The control system, comprising an operator control panel, two encoders (or position sensing devices), a programmable logic controller (such as the Triangle Research International Inc. T100 MD+), a power supply and a plurality of valves. 
         [0040]    The operator control panel shown in  FIG. 6  comprises multiple three position toggle switches  302  for each valve shown on  FIG. 5  item  201 , each position of the toggle switch performs a function either directly controlling the valve or providing an input signal to the programmable logic controller shown in  FIG. 5  item  203 . When the button is in the middle position the valve is not powered and the clamp is driven to the clamping position. When the toggle switch is moved into the “SET” position, the switch provides a voltage signal to the programmable controller. The programmable controller uses this signal to save the position of the table via the position sensing device. The programmable controller is programmed (see program listing ***) to provide a digital output to the corresponding valve when the table is inside the programmed area. Note the “SET” position of the toggle switch is a momentary position (when released it moves back to the middle position) this action turns the signal to the programmable control off. When the table moves out of the position programmed into the programmable logic controller the programmable controller turns the digital output to the valve off, causing the clamp to extend back into the clamping position. 
         [0041]    The fact that the toggle switch (item  302  of  FIG. 6 ) has three positions is immaterial, since the control panel could perform the same function using three switches to control the valve and the signal to the programmable logic controller. This implementation simply serves as an easy method of illustrating the use of the controller. 
         [0042]    In this implementation the encoders are attached directly to the lead screws of the milling machine as shown in view  FIG. 1  item  110 . The encoders ( FIG. 7  item  400 ) used in this implementation are a purchased item (US Digital P/N E6D) and are designed by the manufacturer to be mounted to the rotating shaft and the surrounding structure.  FIG. 7  shows a cross section of a typical encoder mounting. In  FIG. 7  each of the parts making up the encoder assembly are shown. They include the sensor head item  401 , the encoder dial item  404 , the encoder cover item  405 , and the shaft clamp item  402 . Additionally, a milling machine lead screw item  403  and the encoder mount item  406  are also shown. 
         [0043]    The encoder functions in the traditional way for such a device i.e. as the lead screw  403  turns the encoder dial  404  also turns. The encoder dial  404  is made of transparent plastic or glass but has marking on it. The sensor head  401  comprises a light source and a light sensor (not shown), as the encoder dial turns the sensor head responds to each marking causing a pulse to the programmable logic controller. 
         [0044]    The above description mentions the movement of the clamp with the controller monitoring the position of the table and thus the clamp position. This is typical of milling machines which move the table which holds the work piece. So the clamp (fixed to the table) moves with the table, the cutting tool rotates on a stationary spindle. 
         [0045]    In the case of a router (typically used for plastics or wood) the table is stationary and the cutting tool spindle is moved. In this case, the control system would function in essentially the same manner however it would monitor the position of the spindle instead of the table. 
         [0046]    In the above descriptions the use of milling machine examples has been used. This device could easily be adapted for use on a device which uses other methods of manipulating the work piece. For instance laser cutting or engraving, water jet cutting or engraving, chemical etching, electrical discharge machining (a.k.a. EDM) or any other method of manipulation requiring access to the work piece surface. 
         [0047]    To assist and help understand the claims of the clamping mechanism the following definitions are to be used. Also, in  FIG. 4  the distance between the two base holes is labeled  101 , this dimension is used to identify the relative lengths of the structural parts defined below. 
         [0048]    Linkone is defined as a structural piece as shown in  FIG. 4  part  5 . Additionally this part will have the additional restriction of having the two holes being approximately 0.62 distance apart relative to the distance of the two base holes. As an example given that the base holes are 30 mm apart then the distance of the spacing of the two holes in linkone is to be 30×(0.62) mm or 18.66 mm. Also linkone will include a foot surface as shown in  FIG. 4 . 
         [0049]    Linktwo is defined as a structural piece as shown in  FIG. 4  part  6 . Additionally this part will have the additional restriction of having the two holes being approximately 0.31 distance apart relative to the distance of the two base holes. As an example given that the base holes are 30 mm apart then the distance of the spacing of the two holes in linktwo is to be 30×(0.31) mm or 9.4 mm. However, linktwo for the purposes of this discussion will include an implementation of two identical pieces or a single piece, the two pieces are used in an implementation only to provide for stability and ease of manufacturing. 
         [0050]    Linkthree is defined as a structural piece as shown in  FIG. 4  part  7 . Additionally this part will have the additional restriction of having the three holes being approximately 0.55 and 0.64×0.85 distances from the center hole relative to the distance of the two base holes. As an example given that the base holes are 30 mm apart then the distance of the spacing of the first hole in linkthree is to be 30×0.55 mm or 16.6 mm. 
         [0051]    Cablejacketpivot is defined as a structural piece as shown in  FIG. 3  item  14 . This part comprises a tapped hole for mounting a push/pull cable jacket and two side pivots as shown. 
         [0052]    Base is defined as a structural piece as shown in  FIG. 3  item  24 . Additionally, the pivot holes and placement of a hole for the spherical pivot are located on the part assuming positions based on the spacing of the base holes. For instance the horizontal position of the mounting hole for the spherical pivot refer  FIG. 4  feature  8  is 0.16×30 mm (using the example of the definition of linkone). 
         [0053]    The pivotpin is defined as a pin of sufficient length and diameter as to provide for the support of and connection between two parts. Said pivotpin diameter is to be additionally constrained to allow relative rotation of said two connected parts. 
         [0054]    Retractarea is a rectangular area (as shown in  FIG. 8  feature  600 ) which surrounds the clamp linkage linkone. The program used in the programmable logic controller of the controller causes the clamp to retract from the work piece as the cutting tool is inside this area. This area is established when the corresponding toggle switch is pressed into the “Set” position. A complete program listing is provided in appendix A.