Abstract:
A reconfigurable tool changer allows a tool cartridge to be easily attached to, or detached from, a standard machine-tool spindle head. The modular design, includes a revolving tool cartridge having a plurality of tool holders, a meshing gear for engaging a tool holder with the spindle of the machine tool, and an adapter block for positioning the revolving tool cartridge on any standard machine-tool spindle head. The adapter block allows the automatic tool changer to be easily coupled to a wide variety of commercial machine-tool spindles, making the invention a truly reconfigurable and portable tool changer. The revolving tool cartridge incorporates a novel three-dimensional cam structure mechanism, which allows tool indexing to be achieved by means of only one actuator.

Description:
STATEMENT OF GOVERNMENT RIGHTS 
     This invention was made at least in part with Government support under NSF Contract No. EEC 9529125. The Government has certain rights to this invention. 
    
    
     FIELD OF THE INVENTION 
     In general, the present invention relates to automatic tool changers for machine tool spindles. More particularly, the invention relates to an automatic tool changer having a revolving holder to carry, index and drive a plurality of tools. 
     BACKGROUND OF THE INVENTION 
     Automatic tool changers have been developed in response to the need of the machine-tool industry to perform multiple operations in a single set up, to re-tool quickly in order to accommodate product designs that are changing in timely response to market demands, and to be able to replace quickly a worn out or broken part. The typical solution to this problem utilizes a large library of tools stored in a tool storage magazine and accessible through various mechanisms, such as rotating arms, robots, rails and the like. 
     FIG. 1, for instance, shows the automatic tool changer described in U.S. Pat. No. 5,300,006 (JP 7060586), which incorporates a tool storage magazine mounted on a frame, the frame capable of sliding in and out of storage and rotating to replace a tool in a tool-engaging fixture, which is connected to the machine-tool spindle. The tool-changing operation is computer-controlled by means of an input terminal mounted on the machine frame. This type of solution to the frequent re-tooling problem produces large and complex tool changing equipment, which is expensive and cumbersome, at least for more modest operations or for operations requiring more flexibility and agility in response to changing market demands. 
     Another solution has been to house in the machine-tool spindle head an integrated tool cartridge or tool turret of about six different tools so that the proper tool is indexed into position as and when needed. A machine-tool revolving head, which is typical of the prior art and described in U.S. Pat. No. 5,146,663, is shown in FIG.  2 . The prior-art revolving head incorporates a fixed frame, which is fitted with a turret having multiple tool-bearing spindles. The arrangement includes a driving shaft, which is connected at one end to a driving gear, and at the other end through a set of gears to the tool-bearing head of the spindle. The turret moves axially and rotates with respect to the frame by means of a hydraulic driving mechanism, which includes an axial piston, a rotary piston and a chamber. 
     One problem with integrating the turret or tool cartridge with the spindle head is that each time a new set of tools is needed, either the entire spindle head and tool turret assembly must be replaced, necessitating elaborate realignment procedures, or each tool must be replaced individually in a time-consuming and elaborate manner. To avoid realignment, save time and increase productivity while reconfiguring a machining system, it is desirable to be able to swap quickly a tool cartridge from one machine to another without elaborate procedures. 
     SUMMARY OF THE INVENTION 
     The subject invention provides a reconfigurable automatic tool changer (RATC), which allows a tool cartridge to be easily attached to or detached from any standard machine-tool spindle head. In the preferred embodiment, the reconfigurable automatic tool changer (RATC) is based on a modular design, comprising a revolving-head unit, or tool cartridge, having a plurality of tool holders, a meshing gear for engaging a tool holder with the spindle of the machine tool, and an adapter block for positioning the revolving-head unit on any standard machine-tool spindle head. The adapter block allows the RATC to be easily coupled to a wide variety of commercial machine-tool spindles, giving the subject invention a degree of portability not found in the prior art. The revolving head unit or tool cartridge also incorporates an inventive mechanism which allows tool indexing to be achieved by means of one actuator only, in contrast to prior art-designs. 
     This invention represents a substantial departure from prior art practice. In contrast to prior-art designs, the RATC is modular and portable, allowing the same revolving head-unit or tool cartridge to be used for various machine tool spindles. Compatibility is achieved by custom-designing the adapter block, rather than the revolving head, a task which is easier, more efficient and less costly. The tool holders on the revolving head are driven by the machine spindle head through a standard, off-the-shelf spur gear, which meshes with a corresponding gear on the tool holder. A single motor on the adapter block drives the revolving head unit and accomplishes the indexing function of the revolving head through a three-dimensional cam structure. This cam structure includes a set of bevel gears and indexing arms spaced at a distance equal to the radius of the cam circle, in order to accommodate three to six tools in a set. 
     The inventive design of the revolving-head unit or cartridge and the modularity of the entire adaptable automatic tool changer device create a simpler, more efficient and portable structure which is easier to reconfigure and does not require duplication of existing equipment in a manufacturing setting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a drawing which shows a prior-art automatic tool changer disclosed in U.S. Pat. No. 5,300,006; 
     FIG. 2 is a drawing which shows a prior-art automatic tool changer disclosed in FIG. 2 of U.S. Pat. No. 5,146,663; 
     FIG. 3 is a side view of a preferred embodiment of the invention positioned on a machine-tool spindle; 
     FIG. 4 is an enlarged view of the revolving-head unit (tool cartridge) of the invention; 
     FIG. 5 a  is a plan view of an embodiment of the upper cam according to the invention; 
     FIG. 5 b  is a plan view of an embodiment of the lower cam according to the invention; 
     FIG. 5 c  is a side view of an embodiment of the upper cam according to the invention; 
     FIG. 5 d  is a side view of an embodiment of the lower cam according to the invention; 
     FIG. 6 is a plan view of the cam with the driving mechanism; 
     FIG. 7 shows the preferred embodiment of the indexing mechanism; 
     FIG. 8 a  is a top view of an embodiment of the adapter block; 
     FIG. 8 b  is a side view of an embodiment of the adapter block; 
     FIG. 9 shows the use of the invention in different types of commercial spindles; 
     FIG. 10 a  shows a production transfer line before reconfiguration; 
     FIG. 10 b  shows a production transfer line after reconfiguration using the invention; 
     FIG. 11 a  shows a machine tool using the invention with a cartridge including a four-bit gang drill and a four-bit reamer; 
     FIG. 11 b  shows a machine tool using the invention with a cartridge including a drilling, a reaming and a tapping tool; 
     FIG. 11 c  shows a machine tool using the invention with a cartridge including three drill bits of different sizes; and 
     FIGS. 12 a  through  12   e  show a model of the indexing mechanism in five progressive positions a through e. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Having discussed the prior-art systems of FIGS. 1 and 2, reference is made to FIG. 3, which shows a preferred embodiment of the reconfigurable tool changer according to the invention. A revolving head unit (cartridge)  4  includes a set of tool heads  1 , typically three to six, and each tool head further incorporates a gear  2 . The revolving head unit (cartridge)  4  incorporates an upper cam  5 , and a lower cam  6  with an indexing and driving mechanism  9 . An adapter block or unit  11  is used to position the revolving head unit (cartridge)  4  on the spindle of a machine tool. A meshing gear  3  is mounted on the machine-tool spindle and engages the selected tool head. A motor  10 , typically sits on the adapter block  11  and engages the driving mechanism of the revolving head unit (cartridge)  4 . 
     The motor and meshing gear are standard units, and may be acquired separately and kept on hand for use with more than one revolving head unit, if desirable. The adapter block  11  may be custom-made for each machine tool spindle head, if the machine tool configuration so requires, but making an adapter is a straightforward and inexpensive task. 
     The revolving head unit (tool cartridge)  4  is attached to the adapter block  11  by a rod  7  and spring unit  8 , which are also designed to give added rigidity to the revolving head unit (cartridge), and can be custom-made for different applications. The axis of the revolving head unit (cartridge)  4  is at an angle, typically 45°, with the axis of the tool head 
     In the embodiment shown in FIG. 3, the axis of the selected tool head is parallel to the axis of the machine-tool spindle when the meshing gear  3  and tool-head gear  2  are engaged. Gear  2  on the tool head and meshing gear  3  on the spindle are typically standard, off-the-self, spur gears, although it would be obvious to a person skilled in the art to replace these gears with a set of bevel gears to create alternate designs for situations requiring that the tool head axis and the axis of the spindle were not parallel. An additional way to accomplish the meshing of gears  2  and  3  in the event that their respective axes were not parallel would be to adjust the angle of the inclined face of the adapter block shown in FIG.  8 . 
     FIGS. 8 a  and  8   b  show respectively a top view and side view of the adapter block or unit. The adapter unit  11  has a flat bottom surface  20  designed to rest on the machine-tool spindle head. The top surface of the adapter unit  11  has an angled section  22  on which the revolving head unit (cartridge) is positioned and, in the preferred embodiment, a flat surface  24  on which the motor driving the indexing mechanism sits. 
     As mentioned, the adapter is typically custom-machined for a particular spindle. In other embodiments, the motor may be placed directly on top of the machine-tool spindle head. The adapter  11  is secured on the spindle head with screws or other fasteners, preferably through pre-drilled holes  26 . The angled surface of the adapter block has a pre-tapped hole  28  to receive the adapting rod  7  (in FIG. 3) connecting the revolving head unit with the adapter block. In addition, there are four wedge holes  30  on the angled surface. These holes or apertures will receive the wedges  32  attached on the lower cam  6  (see FIGS.  5 ( b ) and (d)) and will prevent the rotation of the lower cam  6  with respect to the adapter block. The adapter block has a slot  42  for a shaft  44  through which the driving mechanism, shown in FIG. 7, is connected with the motor. To facilitate access for fastening the adapter block onto the spindle head through the pre-drilled holes  26 , cutouts  21  may be conveniently machined on the adapter block. 
     The revolving head unit (cartridge)  4  employs an inventive special three-dimensional cam structure to reduce the number of actuators needed to index the revolving head unit (cartridge). The cam structure includes a circular upper cam  5  and a circular lower cam  6  as shown in FIG.  3  and in more detail in FIG.  5 . Plan views of the upper and lower cams are shown in FIGS. 5 a  and  5   b , respectively. The upper cam is engaged to the lower cam through pegs  23  received by holes  25 , and through lugs  29  fitting into slots  31 . The lugs  29  and slots  25  have a cycloid profile, so that there is no interference as the upper cam lifts and rotates about its axis by means of the driving mechanism. 
     FIG. 6 shows the driving mechanism and the indexing mechanism. The indexing mechanism includes two plates  46 , each plate having two rods or indexing arms  48 . The plates are connected to the bevel gears of the driving mechanism, an embodiment of which is shown in FIG.  7 . When the distance between the indexing arms  48  is equal to the radius of the cam circle, so that the indexing arms  48  can engage the upper cam through six grooves  27  equally spaced along the circumference of the upper cam, the revolving head unit (tool cartridge) can support six tool holders. The grooves  27  have involute profiles so that they can engage with the straight rods  48 . 
     Two diametrically opposite rods are in the respective grooves at all times. Shaft  44  is connected to a motor and drives the bevel gear  50 , which is engaged to bevel gears  52  in FIG. 7 connected to plates  46 . As the plates rotate, the indexing arms  48  cause the revolving head unit (cartridge) and attached upper cam to lift, compressing the spring in the spring unit  8 , and rotate with respect to the lower cam so that one of the tool holders comes into alignment with the spindle head axis. FIG. 12 illustrates the rotation and lift of the upper cam in five progressive positions, FIGS. 12 a  through  12   e . At the position of FIG. 12 a , the spring  8  is not compressed, and the plane formed by the visible indexing rods  90 ,  91  is horizontal, while the upper cam  5  and lower cam  6  are engaged. At the position of FIG. 12 b , the plates  46  have rotated lifting the upper cam  5  and causing the spring  8  to be compressed as the indexing rods  90 ,  91  form a plane at an angle with the horizontal. At the position of FIG. 12 c , further rotation brings the upper cam  5  to its maximum lift and the spring to its maximum compression, while the plane formed by the indexing rods  90 ,  91  is vertical. Further rotation lowers the upper cam  5  and relaxes some of the spring compression, as shown in FIG. 12 d . Finally, at the position of FIG. 12 e , the upper cam  5  is lowered to a new position engaging with the lower cam  6  and the spring has returned to its original length. The plane formed by the indexing rods  90 ,  91  is horizontal again, but the rods have exchanged their position through a 180° rotation. When six grooves are present, a 60° rotation causes the next tool holder to be rotated in position for engagement with the spindle head. The distance between indexing rods can be adjusted so that the revolving head unit (cartridge) may accommodate a different number of tool holders, in which case the angle of rotation will change accordingly. 
     FIG. 9 illustrates four examples of using the reconfigurable automatic tool changer with different types of commercial spindle heads. The adapter block is designed in each instance to accommodate differences in the geometry of the machine tool spindle. 
     FIG. 10 illustrates the use of the automatic tool changer to reconfigure a production transfer line in response to changes in production volume. Before reconfiguration, two products have the same demand, and each go through a transfer line of three machine tools, e.g. drilling, reaming, tapping, FIG. 10 a . When the demand for one product drops, while the demand for another increases, the two lines can be quickly reconfigured using the subject invention. The six machines are rearranged so that one transfer line includes five dedicated machines (one drilling, two reaming and two tapping machines) for the product with increased demand. The other line simply uses one machine, which is now equipped with a RATC that incorporates drilling, reaming and tapping tools, FIG. 10 b , for the product with the decreased demand. 
     FIG. 11 illustrates how to accommodate frequent changes in production requirements by simply changing the tool cartridge (i.e. the revolving head unit (cartridge) of the RATC) on the adapter already sitting on the machine-tool spindle head, or by changing the set of tools in the cartridge. Tool cartridges housing a small number of tools provide an efficient way to accomplish the required reconfiguration, because they do not tie up a large number of tools in a fixed configuration that may experience repeated downtime periods, and they can be quickly replaced without the need for realignment. 
     In particular, FIG. 11 shows the reconfiguration of a machine tool for three different products. FIG. 11 a  shows a cartridge having a four-bit gang drill and a four-bit reamer, FIG. 11 b  shows a cartridge including a drilling, a reaming and a tapping tool, and FIG. 11 c  shows a cartridge having three drill bits of different sizes. 
     Although the indexing and driving mechanism described represent the preferred embodiment, other commercially available similar means may be used to accomplish the same purpose. The advantage of the design of the preferred embodiment is that it only requires one actuator for the indexing motion, and it uses simple and commonly available components, such as bevel gears. 
     The overall design of this reconfigurable tool changer offers the advantages of a modular design, in which the same basic resources, i.e. a revolving head unit (cartridge) with a number of tool holders, are portable and can be used in any type of spindle, by adding an adapter block and a meshing gear. The easily reconfigurable and modular design achieves quick assembly or disassembly of the tool cartridge from the spindle, thereby improving machine-tool utilization time and increasing productivity.