Abstract:
A pneumatic drilling machine is provided, comprising a pneumatic motor, a circuit for connecting the motor to a source of compressed air, a tool holder spindle, and a drive mechanism. The drive mechanism comprises a coupling shaft which can be moved to select a first mode of driving the spindle and a second method of driving the spindle. The mechanism has a driving cycle which comprises a stationary mode at the beginning and end of the cycle, and at least one phase for driving the spindle according to the first driving method, then a phase for driving the spindle according to the second driving method, then the stopping of the supply of air to the motor. A supply valve of the circuit is controlled pneumatically by the drive mechanism to interrupt the supply of compressed air to the motor at the end of the driving cycle.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the field of pneumatic drilling machines, more specifically, pneumatic drilling machines which automatically terminate the supply of compressed air to the machine after a drilling cycle is complete.  
       BACKGROUND OF THE INVENTION  
       [0002]     Positive feed pneumatic power drilling machines are widely used in many industries. Such drilling machines normally have a single motor for turning a spindle through a drive gear train. The spindle is threaded into a feed gear that turns at a predetermined rate faster than the turning rate of the spindle for advancing the spindle as the drill progresses through a work piece. The feed gear is driven by a gear train from the same motor as the drive gear train. The gear ratio of the drive gear train is selected to be slightly less than the gear ratio of the feed gear train so the feed gear will turn slightly faster than the drive gear. In that way, the spindle is advanced a predetermined amount for each turn. Once the spindle has been advanced sufficiently, a mechanism is actuated to disengage the spindle feed gear train from the motor and lock it in place. As the motor continues to drive the spindle in the same direction, the spindle threads turn inside the locked feed gear to rapidly retract the spindle.  
         [0003]     Prior art mechanisms for disengaging the gear trains from the motor have included mechanical switches for interrupting the supply of compressed air to the motor. The inclusion of mechanical switches in a pneumatic drilling machine have certain disadvantages. First, they are difficult to assemble, requiring delicate placement of the moving parts within the switch. Further, the delicate parts of the switch are prone to wear and tear, and detract from the longevity of the drilling machine as a whole, which otherwise benefits from a reduction in the number of moving parts that pneumatic tools generally provide.  
         [0004]     Another aspect of prior art drilling machines is that they include pneumatic counting devices, for counting the number of drive cycles carried out by the machine. This allows the owner to carry out the required maintenance on the machine at a proper interval. However, a feature of the prior art counters is that they typically have been configured to add one cycle to the total count each time the motor is switched on. This is disadvantageous because a drill user will often turn the drill off, and then on again, a number of times in the middle of the feed mode. Thus, a single feed cycle may be counted as a number of cycles. This has the undesirable effect of indicating that the drill has been used more often than it really has been, and leads to uneconomical servicing of the machine.  
         [0005]     Thus, a need exists in the art for a pneumatic drill with a pneumatically operated switch for turning off the motor. A need also exists for a counting system that counts feed cycles of the drill only at the completion of a feed cycle. It is believed that the present invention addresses these and other needs.  
       SUMMARY OF THE INVENTION  
       [0006]     According to a preferred embodiment of the invention a pneumatic drilling machine with an automatic control system is described.  
         [0007]     In a preferred embodiment, the drilling machine comprises a pneumatic motor, a tool holder spindle, and a drive mechanism connecting the motor to the spindle. The drive mechanism is configured to drive the spindle through a driving cycle, the driving cycle commencing and ending with the spindle being stationary. The driving cycle also includes a feed mode and a retraction mode.  
         [0008]     In a preferred embodiment, the drive mechanism will include a pneumatic circuit and a control valve positioned in the circuit. The control valve is movable between a first position to select the feed mode, and a second position to select the retraction mode.  
         [0009]     A supply valve is provided, positioned in the pneumatic circuit for supplying compressed air to the motor. The supply valve is movable between a closed position in which compressed air to the motor is interrupted and an open position in which air to the motor is supplied. A coupling shaft is also provided for changing the driving mode of the driving mechanism. The coupling shaft is axially biased by a coupling spring into a coupling chamber positioned in the pneumatic circuit.  
         [0010]     The drive mechanism is configured to send, at the end of the driving cycle, a pneumatic signal to the supply valve via the pneumatic circuit, and the supply valve is configured to close upon receiving the pneumatic signal. In a preferred embodiment, the pneumatic signal is a bolus of air expelled from the coupling chamber by the bias of the coupling spring.  
         [0011]     Another aspect of the invention is that the pneumatic circuit includes a connector for receiving compressed air, and the control valve is configured in relation to the pneumatic circuit so that, when the control valve is in the first position the coupling chamber is not open to the connector via the pneumatic circuit, but is open to the shut-off chamber. Yet another aspect of the invention is that the control valve is configured in relation to the pneumatic circuit so that, when the control valve is in the second position the coupling chamber is open to the connector via the pneumatic circuit, but is not open to the shut-off chamber.  
         [0012]     A still further aspect of the invention is that the supply valve includes a shut-off piston positioned within a shut-off chamber and the coupling shaft includes a coupling piston positioned within the coupling chamber. In a preferred embodiment, the diameter of the shut-off piston is at least twice as large as the diameter of the coupling piston. In this embodiment, the bolus of air expelled from the coupling chamber is directed by the pneumatic circuit to the shut-off chamber of the supply valve. The bolus of air raises the pressure in the shut-off chamber to close the supply valve, and hence interrupt the supply of air to the motor.  
         [0013]     A further feature of the invention is that the drive mechanism further includes a cycle counter configured to add one count only at the commencement of a retraction mode of driving the spindle.  
         [0014]     These and other advantages of the invention will become more apparent from the following detailed description thereof and the accompanying exemplary drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  represents a perspective view of a portable pneumatic drilling machine showing features of the invention.  
         [0016]      FIG. 2  is a schematic view showing aspects of a driving mechanism which controls the power supply and automatic shutoff of compressed air supply to the drilling machine of  FIG. 1 , schematically showing aspects of the drive mechanism in standby mode.  
         [0017]      FIG. 3  is the schematic view of the preceding Figure, schematically showing aspects of the drive mechanism in idle mode.  
         [0018]      FIG. 4  is the schematic view of the preceding Figures, schematically showing aspects of the drive mechanism in feed mode.  
         [0019]      FIG. 5  is the schematic view of the preceding Figures, schematically showing aspects of the drive mechanism in retraction mode. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     With reference to  FIG. 1 , a pneumatic drilling machine, generally referred to by the numeral  20 , and method according to a preferred embodiment of the present invention, is described. In general terms, the machine  20  illustrated in the figure is surrounded by a housing  22  and includes a conventional pneumatic motor  24 . The motor is connectable to an external source of compressed air  25  (not shown in  FIG. 1 ) through a connector  26 . A tool holder spindle  28  held by the housing  22  is adapted to be rotatable about its axis A, and to move the tool back and forth along its axis A. A mechanism  30  for driving the spindle and for controlling the movement of the spindle  28  is located within the housing. Drilling tools can be mounted and removed from the spindle in a conventional manner.  
         [0021]     The drive mechanism  30 , which is schematically exemplified in  FIGS. 2-5 , includes a conventional mechanism known as a positive feed drill. An external source of compressed air  25  supplies compressed air to the drive mechanism  30  via the connector  26 . Within the drilling machine housing, the compressed air is circulated, as described herein, through a series of ducts which collectively form a pneumatic circuit.  FIGS. 2-5  exemplify additional features of the present invention, and, in the description below, the terms “lower,” “upper,” “horizontal,” “left,” and “right” relate to  FIGS. 2-5 .  
         [0022]     In a preferred embodiment, the drive mechanism  30  includes a lower gear (or, drive gear) train  32  comprising gears  34 ,  36 ,  38 ,  40 , and  42  intermeshing in series, and an upper gear (or, feed gear) train  44  comprising gears  46 ,  48 ,  50 , and  52  intermeshing in series. The spindle  28  passes through the end gears  42  and  52  of each gear train. The lower and upper gear trains may be stationary, or rotate in various modes, as described herein.  
         [0023]     In the idling mode, power is supplied via the motor  24  to lower gear  34 , which imparts power only to the lower gear train  32 . In this mode, the upper gear train  44  rotates only under frictional connection with the lower gear train  32 , so that lower and upper gear trains rotate at the same speeds, causing the spindle to rotate under power, but not causing the spindle to advance or retract along its axis A.  
         [0024]     In the feed, or advancing, mode, lower gear  34  is supplied with power from the motor  24  as before, but upper gear  46  is caused (as described herein below) to engage via conventional dog collar linkage to lower gear  36 , thus placing both upper and lower gear trains under power. The number of teeth of upper and lower gear trains are selected to differ by preferably one or two teeth, causing the upper (feed) gear  52  to rotate about the spindle  28  at a slightly faster speed than lower (drive) gear  42 . By conventional means, this difference in rotation speeds is harnessed to cause the spindle  28  to advance downwardly at a relatively slow speed through the upper end gear  52  and the lower end gear  42 , while simultaneously rotating clockwise.  
         [0025]     In the retraction mode, lower gear  34  is supplied with power from the motor as before, but upper coupling gear  46  is caused (as described herein below) to move upward to engage by conventional dog collar means a braking disc  54  which is fixed to the housing and unable to rotate. It will be appreciated that, under these conditions, the upper gear  44  train cannot rotate at all. It will be further appreciated that in this mode the lower gear train  32  will rotate faster than the upper gear train by a relatively large difference. By conventional means, this large difference in rotation speeds is harnessed to cause the spindle  28  to retract at a relatively rapid rate through the upper end feed gear  52  and the lower end drive gear  42 , while simultaneously rotating clockwise.  
         [0026]     A further aspect of the drive mechanism  30  is the supply valve  56  positioned between the external compressed air supply  25  and the motor  24 . The supply valve  56  includes a shaped slide  58  movable within a cylinder  60 . The top of the cylinder  60  may be connected by air duct  61  to a micro valve  63  that presents an exposed surface or button  62  for manually activating the micro valve  63  which, in turn, activates the supply valve  56 . The slide  58  is configured so that, upon downward displacement ( FIGS. 3-5 ), it will permit the passage of compressed air from the source  25  via duct  59  through the valve  56  to the motor  24 . At the lower end of the supply valve  56  is a shut-off piston  64  connected to the slide  58 . The shutoff piston  64  resides within a shut-off chamber  66 . A sufficient pressure in the shut-off chamber  66  is capable of lifting the shut-off piston  64  and slide  58  upwards to interrupt the supply of compressed air to the motor  24 . ( FIG. 2 )  
         [0027]     Yet another aspect of the drive mechanism  30  is the coupling shaft  68  which is configured to rotate in, and slide through, lower coupling gear  36  and to rotate in, but to be translationally connected with, upper coupling gear  46 . Thus, any translational movement of the coupling shaft  68  will translationally carry upper gear  46  with it. A coupling spring  70  is positioned to bias the coupling shaft  68  downward. Adjacent the coupling shaft is an idler lock  72 , having an arm  74  configured to removably engage with an indent  76  in the coupling shaft  68 . A torsion spring  78  torsionally biases the idler lock  72 . Fixed above the upper gear  46  is the braking disc  54  fixed to the housing and unable to rotate, so that an upward movement of the coupling shaft  68  engages upper gear  46  with the braking disc  54 , a downward movement of the coupling shaft engages gear  46  with gear  36 . In an intermediate position, the coupling shaft  68  is free from connection with either the brake disc  54  or the lower gear  34 . Connected to the lower end of the coupling shaft  68  is a coupling piston  80  residing within a coupling chamber  82 . A sufficient pressure in the coupling chamber  82  is capable of lifting the coupling piston  80  and coupling shaft  68  against the bias of the spring  70 .  
         [0028]     Another aspect of the drive mechanism  30  is the control valve  85  that includes a shaped stem  86  sliding within a cylinder  88 . A supply of compressed air is brought directly from the compressed air source  25  to the control valve  85  by a duct  90 . The control cylinder  88  is connected via a duct  92  with the coupling chamber  82 , and via a duct  94  with the shut-off chamber  66 . The control valve  85  is configured to have two modes, corresponding with two vertical positions of the shaped stem  86  within the cylinder  88 . In a first mode, the stem  86  is in an upper position and configured to pneumatically connect the coupling chamber  82  with the shut-off chamber  66  via duct  92  and duct  94 , but prevent the supply of compressed air  25  to both the shut-off chamber and the control chamber, as exemplified in  FIG. 2 . In a second mode, the stem  86  is in a lower position and permits compressed air to be fed from the compressed air source  25  to the coupling chamber  82 , but interrupts the pneumatic connection between the coupling chamber  82  and the shut-off chamber  66 , as exemplified in  FIG. 5 .  
         [0029]     The vertical position of the stem  86  of the control valve  85  may be set by movement of the spindle  28 , as follows. An upper spindle nut  98  is attached to the spindle  28  so that downward movement of the spindle brings the upper spindle nut  98  in contact with an upper valve arm  100  to move the stem  86  downwards. A lower spindle nut  102  is attached to the spindle  28  so that upward movement of the spindle brings the lower spindle nut in contact with a lower valve arm  104  to move the stem upwards.  
         [0030]     A further aspect of the drive mechanism is that it includes a pneumatic counting device  106 , pneumatically connected with coupling chamber  82  via duct  108 . The counting device may be a commercially available counting device such as Part No. PM1421 by Ellis/Kuhnke Controls, of Atlantic Highlands, N.J. 07716. The counting device is adapted to count the number of drive cycles performed by the drilling machine so that service requirements on the machine may be performed as required. Each time compressed air is delivered to the coupling chamber  82  (as described herein below), the counting device will add one cycle to the total number of cycles counted.  
         [0031]     In use, the drilling machine  20  may be operated as follows.  
         [0032]     The drive mechanism is initially configured in a standby mode, as schematically represented in  FIG. 2 . In standby mode, the supply valve  56  is closed in a first position, thus interrupting supply of compressed air  25  to the motor  24 . The coupling shaft is in an intermediate position, held in place by the arm  74  on the idler lock  72 . The control valve  85  is in an upper first position with the slide  86  interrupting supply of compressed air to the coupling chamber  82 .  
         [0033]     The standby mode may be followed by the idle mode, as schematically represented in  FIG. 3 . The motor is activated by manually depressing the start button  62 . The momentary opening of the micro valve  63  directs an air signal above the slide  58  of the supply valve  56  via the duct  61  displacing the slide to open the supply valve, and thus opening the compressed air supply going to the motor  24 , to cause the motor to turn and supply power to lower gear  34 , and hence to the entire lower gear train  32 . At this stage the coupling shaft  68  is positioned in an intermediate position so that gear  46  is engaged with neither the brake disc  54  nor lower gear  36 . In this position the drive mechanism  30  is in the idle mode, with the spindle  28  under rotational or driving power from the lower gear train  32 , but not under translational or feeding power.  
         [0034]     The idle mode may be followed by the feed mode, as schematically represented in  FIG. 4 . In order to engage the upper gear train  44  to advance the spindle  28 , the idler lock  72  may be turned sufficiently to allow the arm  74  to disengage from the indent  76  in the coupling shaft  68 . This will allow the coupling shaft  68  under the biasing action of the spring  70  to move down and engage the upper coupling gear  46  with the lower coupling gear  36 . The tool now enters the feed, or advancing, mode, with the spindle  28  rotating and being advanced slowly under power. The feed action of the spindle will continue until the upper spindle nut  98  reaches and pushes down on, the upper valve arm  100  to depress the stem  86  within the cylinder  88  of the control valve  85 , as exemplified in  FIG. 5 , thus leading to the retraction mode, as detailed below.  
         [0035]     The feed mode may be followed by the retraction mode, as schematically represented in  FIG. 5 . The downward movement of the control valve stem  86  allows compressed air to flow into the coupling chamber  82 , forcing up the coupling piston  80  and hence the coupling shaft  68 , thereby ending the spindle feed process by disengaging the upper coupling gear  46  from lower coupling gear  36 , and locking the upper gear  46  against the brake disc  54  of the upper housing. The immobilization of the upper gear train  44  will initiate the retraction phase (or return cycle) characterized by a fast return of the spindle (about  1  mm per revolution), until the lower spindle nut  102  reaches and elevates the lower valve arm  104 , returning the valve stem  86  to its first upper position, as exemplified in  FIG. 2 , thereby to end the retraction mode, as set forth below.  
         [0036]     The return of the valve stem  86  to its first position firstly disconnects the compressed air supply  25  from the coupling chamber  82  ( FIG. 2 ), and, almost simultaneously, connects duct  94  with duct  92 , thus pneumatically connecting the coupling chamber  82  with the shut-off chamber  66 . It will be appreciated that when the stem  86  was in its second lower position, the pressure in duct  94  was around atmospheric pressure, but the pressure in the coupling chamber  82  was under compression from the source  25 , which may be in the region of 90 p.s.i. Thus, when the upward movement of the stem  86  disconnects the coupling chamber  82  from the compressed air supply  25 , but connects the coupling chamber  82  to the shut-off chamber  66 , the compressed air present in the coupling chamber  82  is at an elevated pressure (i.e. well above atmospheric pressure) and will rapidly discharge into the shut-off chamber  66  until the pressure in both chambers  82  and  66  and their related ducts is equalized. Furthermore, at the same time, the coupling spring  70  biases the coupling piston  80  downwards, adding to the escape of air from the coupling chamber  82  into the shut-off chamber  66  by expressing an additional volume, or  37  bolus,” of air (about 0.1 cu. inches) from the coupling chamber  82 . It will be appreciated that the resulting upward force applied to the shut-off piston  64  will lift the supply valve slide  58  to its upper first position ( FIG. 2 ) to cut connection of the main air supply  25  to the motor  24 , thus shutting off the motor  24 . The drive mechanism is now in standby phase, the same condition it was in prior to pressing button  62 . To start the whole cycle over, the user may press button  62  once again.  
         [0037]     It will be appreciated that the manner in which the supply valve  56  is closed, as described in the preferred embodiment, may be accomplished by transmitting a pneumatic signal directly to the supply valve via the pneumatic circuit within the housing, specifically by the ducts  92 ,  94 . Thus, in a preferred embodiment, the force applied upon the valve  56  to move it to a closed position is a positive pneumatic force, i.e., a force not applied by a mechanical action upon the supply valve itself. Moreover, in another aspect, the source of the pneumatic signal may derive from a fixed quantity of air trapped at elevated pressure within a reservoir located in the drive mechanism. In a preferred embodiment, the reservoir may include the coupling chamber  82 , its supply duct  92 , and also may include a volume defined by the cycle counting device  106  and its supply duct  108  if present. The fixed quantity of air trapped at elevated pressure within a reservoir located in the drive mechanism may be distinguished over an effectively limitless supply of compressed air from the main source of compressed air  25  which is not trapped in the drive mechanism.  
         [0038]     A significant aspect of a preferred embodiment of the invention is that the ending position of the slide  86  of the control valve  85  at the end of a drilling cycle is the same as its starting position prior to activation of the drilling cycle, and that, at both the start and the end of a drilling cycle (as seen in  FIG. 2 ), the main compressed air supply  25  to the motor  24  is closed by the supply valve  56  and the compressed air supply to the coupling chamber  82  is closed by the control valve  85 , thus giving rise to a completed cycle of operation in all respects. If, for example, the slide  86  connected the compressed air supply  25  with shut-off chamber  66  upon the upward movement of the slide  86  at the end of a drilling cycle, the compressed air has raised the slide  58  to turn off the motor  24 . However, it will be appreciated that compressed air would now be supplied to the shut-off chamber  66  at the start of a new drilling cycle, a condition which may prevent the slide  58  from being downwardly activated, with disruptive consequences.  
         [0039]     An additional aspect of the drilling machine is the emergency valve  110  with its activation button  112 . The valve  110  is also a micro valve, configured to direct compressed air from the source  25  direct to the shut-off chamber  66  of the supply valve  56  via a duct  114 . As will be appreciated, the compressed air in the shut-off chamber  66  will force the slide  58  of the supply valve upwards to interrupt air supply to the motor  24 . In case of an emergency, depressing the activation button  112  will activate the micro valve  110  which in turn will shut off the supply valve  56  and the motor  24 . A bleed hole in the shutoff chamber  66  allows for the decompression of the chamber  66 , thus allowing the supply valve  56  to be turned on again.  
         [0040]     A further significant feature of a preferred embodiment of the invention is that the cycle counter  106  is pneumatically connected to the coupling chamber  82 . This has the advantage that a driving cycle is only counted once the spindle has completed a feed phase, marked by the advance of the control valve  85  to its second position, upon the drive mechanism entering the retraction phase. Accordingly, if the emergency shutoff valve  110  is activated by pressing emergency button  112  in the middle of a feeding phase, an additional cycle will not necessarily be added to the counter when the motor is turned on again. Only upon the commencement of a retraction phase will the counter add one cycle to the total. It will be appreciated that this feature has an advantage over systems that add one cycle to the total every time the motor is switched on. In such machines, interrupted but recommenced drive cycles count as a full cycle upon each recommencement, thus biasing the total count to a higher level than actually carried out by the drilling machine, and leading to uneconomical servicing of the machine or replacing its accessories such as drill bits.  
         [0041]     Thus, the preferred embodiments of the invention provide for an inexpensive and reliable device and method for automatically controlling a drilling machine. The use of a pneumatic control over the supply valve  56 , which controls the supply of compressed air to the drive mechanism, eliminates the dangers present in the use of mechanical parts which tend to wear down during the lifetime of a drilling machine. Moreover, a pneumatic control system is typically easier to assemble than a mechanical control system, and eliminates much of the labor intensive operation of assembling the small mechanical pieces of a mechanical control system.  
         [0042]     While a particular form of the invention has been illustrated and described, it will also be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.