Abstract:
A machine tool system with a primary motor and a first slave motor, each motor operably being adapted to drive a separate sub-system within the machine tool system, wherein a control system operably controls the speed of the first slave motor at a predetermined speed relative to the speed of the primary motor.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to machine tool systems, and in particular to multi-spindle automatic bar machines.  
         BACKGROUND OF THE INVENTION  
         [0002]    Conventional multi-spindle automatic bar machines have complex gearing mechanisms that allow various parts of the machine to rotate at pre-selected speeds, power being provided by a single standard electric motor.  
           [0003]    [0003]FIG. 1 shows in simplified form the gear layout for a five spindle automatic bar machine with a conventional single motor drive. The machine has a head HI that rotates stepwise about axis A-A′ and has an inner face F 1  with five equidistantly spaced work spindles P 1  each of which is linked by a shaft and gear wheel (not shown) to a ring gear G 1  having teeth on both the inside and outside of the ring. The outer teeth of ring gear G 1  are driven by a conventional AC electric motor M via shaft S 1  and gear wheels G 2  and G 3 . Thus, as the ring gear G 1  rotates about axis A-A′ all five work spindles P 1  also rotate about axes B-B′. Head H 1  revolves stepwise about axis A-A′ as a result of the rotation of cross slide cams CA 1 .  
           [0004]    Adjacent to and spaced some distance apart from inner face F 1  of revolving head H 1  is a stationary head H 2 . This head has five equidistantly spaced tool spindles P 2  arranged on the same pitch circle as the work spindles P 1 . Thus, during the machining steps the tool spindles P 2  and the work spindles P 1  are aligned so that axes B-B′ are coaxial with the center lines C-C′ of tool spindles P 2 . During the so called “indexing phase” head H 1  rotates (in this case by 72 degrees) so that each work spindle is aligned with a new tool spindle.  
           [0005]    Four of the five tool spindles P 2  are stationary but one is usually rotatably mounted for threading and is connected via shaft S 2 , gears G 4 , G 5 , G 6 , shaft S 3 , clutch C 1  and shaft S 4  to gear wheel G 3 . The rotational speed of this spindle can be varied by changing the gearing ratio, for example the number of teeth in wheels G 5  and G 6  or by using a gearbox and extra clutch (not shown). Tools held in spindles P 2  are moved axially (in direction C-C′) by the action of the rotating tool spindle cam assembly CA 2  on cam followers and linkage arms (not shown). Thus as cam assembly CA 2  rotates about its vertical axis the five individual cams each move their associated tool spindle in an axial direction either towards or away from the rotating head according to the contour of each individual cam. Cam assembly CA 2  is driven by shaft S 5  via worm gear G 7 , shaft S 6  and clutch C 2 , gear wheels G 8  and G 9  to shaft S 1 .  
           [0006]    Tools associated with each work spindle (for example a rod cutter) are controlled by cross slide cam assembly CA 1  each cam of which act on a cam follower and linkage mechanism (not shown). Thus as cam assembly CA 1  rotates about its horizontal axis individual cams each move associated tools, relative to the rotating work spindles P 1 , according to the contour of each individual cam. Cam assembly CA 1  is driven via worm gear G 10  by shaft S 7 , bevel gears G 11 , G 12  shaft S 8 , gears G 13 , G 14  and clutch C 3  to shaft S 6 .  
           [0007]    Thus, when the machine is operating motor M drives cams CA 1  and CA 2 , revolving head H 1 , work spindles P 1  and tool spindle P 2 .  
           [0008]    While such systems work reliably they tend to be noisy and require replacement of some gear wheels when tooling for another job. The clutches require constant adjustment if optimal machine output is to be maintained, in practice, this normally proves to be impractical. Tooling up for another job generally requires removal and replacement of selected gears in order to obtain the gear ratios appropriate for the manufacture of the new part.  
         SUMMARY OF THE INVENTION  
         [0009]    It is an object of the present invention to provide an improved machine tool system.  
           [0010]    In one aspect the invention provides a machine tool system with a primary motor and a first slave motor each motor operably being adapted to drive a separate sub-system within the machine wherein a control system is used to control the speed of the first slave motor at a predetermined speed relative to, and/or at a fixed ratio of, the speed of the primary motor.  
           [0011]    Preferably, the control system is computerized such as a computer numerically controlled (CNC) system and/or the motors are electronically driveable such as servo motors like 12V DC servo motors.  
           [0012]    The machine tool system may further comprise a second slave motor wherein the control system is used to control the speed of the second slave motor at a predetermined speed relative to one of the first slave motor and the primary motor.  
           [0013]    A first sub-system may comprise a plurality of rotating work spindles. The rotating work spindles may be mounted on a rotating head. The rotating head may be driven by the primary motor. The first sub-system may be driven by a slave motor,  
           [0014]    A second sub-system may comprise a plurality of cams mounted on at least one shaft.  
           [0015]    A third sub-system may comprise a plurality of tool spindles mounted on a stationary head.  
           [0016]    A fourth sub-system may comprise a plurality of cams mounted on at least one shaft wherein rotation of the cams produces axial movement of the tool spindles. The second and fourth subsystems may be driven by the primary motor.  
           [0017]    A fifth sub-system may comprise means of driving at least one rotatably mounted tool spindle. The fifth sub-system may be driven by a slave motor.  
           [0018]    Preferably, the machine tool system comprises means of detecting the rotational angle of the primary motor and feeding this data to the controller.  
           [0019]    In another aspect the invention provides a control system for a machine tool with a primary motor and at least one slave motor, each motor operably being adapted to drive a separate sub-system within the machine tool system wherein a control system is used to control the speed of the at least one slave motor at a predetermined speed relative to the speed of the primary motor. Beneficially such control system can be retrofittable to a conventional machine tool such as shown in FIG. 1, thereby removing the need for much of the complex drive shaft and gear arrangement described earlier.  
           [0020]    Preferably, a detector is used to indicate the angular position of the primary motor drive shaft.  
           [0021]    Preferably, the control system is computerized such as a CNC system and the motors are electronically driveable such as servo motors.  
           [0022]    Preferably, the degree of axial rotation of the primary motor over a fixed time period is used to determine the required axial rotation of a slave motor over the same time period. The control system may comprise a first and a second slave motor wherein the degree of axial rotation of the first slave motor over a fixed time period is used to determine the required axial rotation of the second slave motor over the same fixed time period. Preferably, the fixed time period is between 0.01 and 0.001 seconds, and more preferably between 0.002 and 0.006 seconds.  
           [0023]    The motors may rotate in both a clockwise and anticlockwise direction. The primary motor may be driven at varying speeds at different stages of the machine cycle. Preferably, the primary motor is driven at a first constant speed during one stage of the machining cycle and a second constant speed during a further stage of the cycle.  
           [0024]    Preferably, the primary motor can be rotated by fractions of a revolution using a hand operated controller interfacing with the control unit. Preferably, the ratio of the speed of the slave motor, or motors or primary motor is set by the operator using a control panel.  
           [0025]    Preferably, settings appropriate to a particular job can be input via operator panel connected to the control unit and set values can be displayed on a screen controlled by the control unit.  
           [0026]    Preferably, each motor unit has integral means of detecting the angular position of the motor shaft. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    An embodiment of the invention relating to a five spindle automatic bar machine will now be described by way of example only, with reference to the following schematic drawings in which:  
         [0028]    [0028]FIG. 1 is a schematic block diagram of a machine tool system according to the prior art;  
         [0029]    [0029]FIG. 2 shows the general arrangement of the motors, gears, spindles and cams for a system according to the invention;  
         [0030]    [0030]FIG. 3 shows selected features of the front face of the work spindle, shown in FIG. 2;  
         [0031]    [0031]FIG. 4 depicts the control arrangement for a system according to the invention employing three servo motors;  
         [0032]    [0032]FIG. 5 is a logic flow diagram for an electronic gearbox according to the invention;  
         [0033]    [0033]FIG. 6 is a logic flow diagram for a so called root program, and according to the invention;  
         [0034]    [0034]FIG. 7 is a logic flow diagram for live data calculations conducted according to the invention in use. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    Referring to FIG. 2, the machine tool system has a head  100  that is mounted so that it may rotate step-wise about axis X to X′ and has an inner face  102  with five work spindles A to E the centers of which lie on a circle, the spacing between adjacent spindles being constant (see FIG. 3). Each spindle A to E is linked by a shaft and a gear wheel (not shown) to the inner teeth of a ring gear  104  having teeth on both the inside and outside of the ring. The outer teeth of the ring gear  104  are driven by spindle servo motor  34  via shaft  106 , gears  108 ,  110 , shaft  112  and gear  114 . Thus, as ring gear  104  rotates about axis X to X′ all five work spindles A to E rotate about respective longitudinal axes, such as Y to Y′ in the case of spindle E.  
         [0036]    Adjacent to and spaced some distance apart from inner face  102  of revolving head  100  is a stationary head  120 . This head has five equidistantly spaced tool spindles F to J arranged on the same pitch circle as the work spindles A to E. Thus, during the machining steps the spindles F to J and the work spindles A to E are aligned so that axis Y to Y′ are coaxial with the center lines of C to C′ of the tool spindles F to J. During the so called indexing phases head  100  rotates (in this case by 72 degrees) so that each work spindle is aligned with a new tool spindle.  
         [0037]    Four of the five tool spindles are stationary but one spindle I is rotatably mounted and connected via gears  130  and  132  (idle gear) and  134  to threading servo motor  40 . Tools held in spindles F to J are moved axially in the direction Y to Y by the action of the rotating tool spindle cam assembly  140  on cam followers and the linkage arms (not shown). Thus, as cam  140  rotates about its vertical axis, five individual cam each move their associated tool spindles F to J either towards or away from the rotating head according to the contour of each individual cam. Cam assembly  140  is driven by feed servo motor  26  via shaft  142 , worm gear  144 , shaft  146 , bevelled gears  148  and  150  and shaft  152 .  
         [0038]    Tools associated with each work spindle (for example a rod cutter) are controlled by cross slide cam assembly  160  comprising individual cams each with a cam follower and linkage mechanism (not shown). Thus, as cam assembly  160  rotates about its horizontal axis each cam moves its associated tool according to the contour of the cam. Cam assembly  160  is driven by servo feed motor  26  via a shaft  162  and worm gear  164  and shaft  152 . Head  100  is rotated step-wise about axis X to X′ being driven by the feed servo motor  26  via Geneva gear  170 , shaft  162 , work gear  164  and shaft  152 .  
         [0039]    Thus, when the system is operating the primary (feed servo) motor  26  drives cam assemblies  140 ,  160  and rotates head  100 , the spindle servo motor  34  rotates work spindles A to E, and the threading motor  40  rotates tool spindle I.  
         [0040]    In use rods of raw material (not shown) are fed step-wise in the direction X to X′ from a cradle (not shown) that also rotates about X to X′, to each work spindle. Each work spindle A to E has a chuck (not shown) that is opened and closed by hydraulic means, the hydraulic pressure being generated by the action of cam followers that engage cams located on shaft  162  within the chuck and feed cam assembly  180 . A rod feeding mechanism that advances the rods through revolving head  100  is also operated by similar hydraulic means to the chuck and feed assembly  180 .  
         [0041]    An absolute encoder  32  detects the angular position of the shaft  162 . This generates data used by the machine tool control system (see later). The absolute encoder allows the machine to be switched off and back on without position loss.  
         [0042]    [0042]FIG. 4 shows the main components of a control system  10  according to the invention which comprises an operator panel  12  having a display screen  14  and operator inputs  16  such as a keypad. The operator panel  12  is connected to an electronic controller such as a microprocessor or CNC controller  18  which can be electronically interfaced by a user using input module connector  20  and/or output module connector  22 .  
         [0043]    There are three servo motors; feed servo motor  26 , spindle servo motor  34 , and threading servo motor  40 . Each of these servo motors is connected to a CNC controller  18  via a respective servo amplifier and interface board, for example feed servo motor  26  is connected by a feed servo amplifier  28  and interface board  30  to the CNC controller  18 . Each servo amplifier is powered by low voltage modular power supply unit  46 . Power unit  46  can be a 12VDC unit for example. Absolute encoder  32  is connected to the CNC controller  18  via interface board  30 .  
         [0044]    Each servo motor has an integral resolver unit that detects the angular position of its drive shaft and two sets of connections to the associated servo amplifier. For example, spindle servo motor  34  is connected to spindle servo amplifier  36  by power cable  48  and also by resolver cable  50 . The resolver unit and cable  50  allow the CNC controller to verify that the servo motor is operating correctly and that it has moved through a specified angular distance.  
         [0045]    An electronic hand wheel  24  connected to CNC controller  18  allows the operator to rotate the primary servo motor  26  by fractions of a revolution in order to set-up the machine.  
         [0046]    Referring to FIGS.  5  to  7  showing the overall control logic for the system. FIG. 5 shows the logic flow diagram for the electronic gearbox. The main function of this part of the control system is firstly to maintain the speed of the spindle servo motor  34  at a fixed ratio to that of the feed servo motor  26 , and secondly to maintain the speed of the threading servo motor  40  at a fixed ratio to the spindle servo motor  34 .  
         [0047]    Live data calculations (see latter) are used to establish live gearbox and bar feed data [step  200 ]. Thus, in use a signal from the absolute encoder  32  is used to calculate how far (angularly) the shaft  162  and cam assemblies  160 ,  180  have moved as indicated at step  202 . This data is then displayed on the operator panel screen  14  [step  204 ]. Then following a first safety check [step  206 ] the gearbox ratio data (established during the live data calculation phase) is used to calculate the required spindle servo motor  34  angular movement step  208 . Providing spindle movement is allowed [step  210 ], the output (angular) spindle motion [step  212 ] is used by the CNC controller  18  to control spindle servo motor  34  via spindle servo amplifier  36  and interface board  38 .  
         [0048]    The controller then decides whether the moving tool spindle I is at the threading in stage or threading out stage [step  214 ]. If it is threading in, it uses gearbox data to calculate the required (inward) angular movement [step  216 ] of the threading servo motor  40 . If it is threading out, it uses the gearbox data to calculate the required angle of movement (in the opposite direction) [step  218 ] of the threading servo motor  40 . Providing motion of the threading spindle is allowed step  220  an output threading motion signal [step  222 ] is generated by the CNC  18  and used to control the threading servo motor  40  by a threading servo amplifier  42  and interface board  44 . Data is then copied to the CNC  18  at steps  224  and  226  prior to a delay step of typically 0.004 seconds [step  228 ] and then returning to step  202 . Thus, the sequence of steps  202  to  228  is repeated every 0.004 seconds. Motion of the tool spindle I is not allowed during the indexing phase (i.e, during movement of head  100 ) and motion of the work spindles may also not be allowed during this phase.  
         [0049]    The electronic gearbox allows the complex shaft and gearing system of conventional machines to be replaced by a much simpler and quieter arrangement. The electronic nature of the gearbox allows an infinite number of ratios to be selected; in contrast to the relatively limited set of values obtainable from conventional machines, and the inconvenience of physically changing gear ratios in such machines.  
         [0050]    A root program, represented schematically in FIG. 6, controls the (primary) feed servo motor  26 . The main function of this part of the control system is to drive servo motor  26  at a set indexed rate during the index phase and at a set working rate during the working phase. Thus, user input data [step  300 ] is used calculate the working rate [step  302 ] and index rate [step  304 ] for the primary servo motor  26  and also the angular range corresponding to the working phase [step  306 ]. Coolant is then started [step  308 ] and further data changes inhibited [step  310 ]. The absolute encoder  32  is then used to determine whether the feed and slide cams  160  and  180  are in the working angular segment [step  312 ]. If they are, the primary servo motor  26  is driven at the working rate to the end of the work angle [step  316 ]; if they are not, the primary servo motor  26  is driven at the index rate to the end of the index angle [step  314 ]. At the end of the working phase, providing a repeat cycle is called for step  318 , the controller returns to the index phase step  314  and thus continually cycles between the index phase [step  314 ] and the working phase [step  316 ]. If a repeat cycle is not allowed the primary servo motor  26  stops at the entry to the index angle [step  320 ].  
         [0051]    Live data calculations are performed by the CNC during a set-up period prior to production as indicated schematically in FIG. 7. Certain parameters are set by the operator, notably:  
         [0052]    Cycle and index time [step  400 ] 
         [0053]    Spindle speed [step  402 ] 
         [0054]    Production method (die, broach,drill or thread) [step  404 )  
         [0055]    Cut direction (LH or RH) [step  406 ] 
         [0056]    Drill/die speed [step  408 ] 
         [0057]    From the cycle time [step  400 ] and spindle speed [step  402 ] the controller calculates the available production revolutions [step  410 ]. The operator can either select the current default settings for start/reversal position, in and out revolutions per minute, and possible threads [step  412 ] or can update these data [steps  414 ,  416 ,  418 ]. The input data are then used to calculate gearbox ratios [step  420 ] and to set up the gearbox trip points [step  422 ]. Finally, the operator sets the bar feed data [step  424 ].  
         [0058]    The system allows increased productivity to be achieved firstly, through reduced tool set-up time and secondly because the production speed can in general be increased. The reduced set-up time results from eliminating the need to change gear trains and the increased productivity results from a generally faster rotating head speed made possible by the elimination of clutch members and the ability to control the primary motor at any desired speed during different parts of the production cycle, the speed of this motor being infinitely variable.