Abstract:
A control system for a paintball marker having a breach, the control system comprising a contact sensor, a controller, and a paintball firing mechanism, the sensor being arranged to be located within the paintball marker, to sense a paintball being in contact therewith and to produce a signal indicative of the presence of the paintball within the breech, and the controller being arranged to receive the signal and to control the actuation of the firing mechanism in response to the signal.

Description:
BACKGROUND OF INVENTION 
   This invention relates to a paintball marker control system. More particularly, but not exclusively, it relates to a control system for regulating the rate of fire of a marker. 
   The control of paintball markers is of great importance both from a safety viewpoint and also with regard to preventing blockages due to paintballs rupturing within the marker. Safety is a major issue due to the ejection of high velocity projectiles, paintballs, from markers and the possibility of the accidental discharge of paintballs in areas where protective clothing is not mandatory leading to injuries. 
   Automatic and semi-automatic paintball markers use a compressed gas that is released in order to fire a paintball, to move a bolt that loads the next paintball ready for firing. The bolt is driven back by the gas in order to allow the next paintball to enter the marker&#39;s breech. When the marker is fired the bolt moves forward, typically under spring action, partially sealing the breech, and a hammer strikes a gas entry valve to open it. The open valve allows the compressed gas to enter the breech and force the paintball out of the marker. Some of the gas is used to move the bolt back to its loading position and the valve closes. 
   For a “perfect” paintball it is possible to fire one paintball every 7 ms. A “perfect” paintball is assumed to be perfectly spherical and to fit exactly in the breech and barrel of the marker. Clearly this is not always the case as paintballs can be filled to varying degrees, deformed and have variable diameters. Thus a timing cycle for firing of 14 ms is typically used in order to allow for imperfections in paintballs. This is a compromise between an efficient use of the compressed gas, which decreases with increased firing cycle time, and allowing for variations in the paintballs to provide a substantially uniform firing characteristic for a marker. 
   The rupturing of paintballs within a marker, either by being “chopped” by the marker&#39;s bolt as they fall into the marker&#39;s breech, or simply by overpressurizing the breech when firing, can result in internal surfaces of the marker becoming coated with paint. Ruptured paintballs can, eventually, result in the marker not firing properly or indeed jamming. 
   Current systems for controlling paintball markers typically employ optical sensors to sense the presence of a paintball in the breech of the marker. These systems seek to prevent the accidental rupturing and/or discharge of paintballs by preventing firing of the marker, for example, when a paintball is not wholly within the marker&#39;s breech. These systems rely on either sensing reflected light from a paintball in the breech or the interruption of a beam of light as a paintball falls into the breech. 
   All such optical control systems have a problem, in that, should a paintball rupture in the breech, the optics of the system can become fouled, rendering the system unreliable or possibly even inoperable. Also optical systems must have their sensors screened from stray light sources in order to prevent spurious output signals. 
   Additionally, reflected light systems have the attendant problem that paintballs typically have multicoloured casings, for example yellow and black, and each colour will have a different reflectivity, thus causing difficulties in measuring the reflected light. 
   Optical beam interruption systems suffer from the disadvantage that as a paintball enters the breech a lower surface of it will break the beam. This allows the marker&#39;s bolt to be thrown forward before the paintball has fully entered the breech and chop the paintball. 
   One particular control system as disclosed in U.S. Pat. No. 5,727,538 utilizes position sensors to monitor the location of the bolt in conjunction with an electronic sensor to detect the presence of a paintball in order to limit the opportunities for chopping of paintballs. The use of a number of sensors is complicated and can lead to difficulties in implementation. This document also discloses the use of a single optical sensor but states that such a sensor is unreliable because the sensor can readily become clogged with dirt or paint from ruptured paintballs. 
   SUMMARY OF INVENTION 
   According to a first aspect of the present invention there is provided a control system for a paintball marker having a breech, the control system comprising a contact sensor, a controller, and a paintball firing mechanism, the sensor being arranged to be located within the paintball marker, to sense a paintball being in contact therewith, and to produce a signal indicative of the presence of said paintball within said breech, and the controller being arranged to receive said signal and to control the actuation of said firing mechanism in response to said signal. 
   It will be appreciated that the term “contact” as used herein is taken to mean a force exerted upon, or movement or deflection of the sensing means. 
   Preferably the contact sensor is a differential sensor, and more preferably, a piezoelectric sensor. Even more preferably the contact sensor is arranged to be located opposite a point of entry of a paintball into the breech. 
   The controller may be arranged to be operable by a user to control said rate of actuation of the firing mechanism in the absence of a signal indicative of the presence of a paintball. The controller may be arranged to be operable by a user to adjust a sensitivity level of the control system to the arrival of a paintball in the breech. The controller may be arranged to threshold the signal to discriminate between the arrival of a paintball in the breech and other vibrations. 
   The system may include a visual status indicator arranged to indicate whether the control system is activated. 
   The controller may be arranged to prevent the actuation of the firing mechanism in the absence of a signal indicative of the presence of a paintball. Alternatively, the control means may be arranged to limit the rate of actuation of the firing mechanism. The controller may in other cases be arranged to define a trigger pull time and to cause firing of a shot at a firing time after said trigger pull time, and to provide a delay period between the trigger pull time and the firing time in the absence of said signal. 
   The control system may include analogue to digital converter for digitising the signal. The control system may be arranged to threshold the signal following its conversion to a digital form. 
   According to a second aspect of the present invention there is provided a paintball marker control system comprising vibration sensor, a controller and an alarm, the sensor being arranged to be located within a paintball marker, and to sense movement of the marker, the controller being arranged to receive a signal from the sensor indicative of the movement of the marker and to control the actuation of the alarm in response to said signal. 
   The alarm may be an audible alarm. Alternatively, or additionally, the alarm may include a visual indicator. 
   The invention will now be described, by way of example only, with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a schematic diagram of a paintball marker including a control system according to a first embodiment of the present invention; 
       FIG. 2  is a block diagram of a control system according to the present invention; 
       FIG. 3  is a schematic representation of an output signal from a sensor of a control system according to the present invention; 
       FIG. 4  is a schematic representation of a series of threshold signals from a sensor of a control system according to the present invention; 
       FIG. 5  is a schematic representation of a grip of a paintball marker including a control system according to the present invention; and 
       FIG. 6  is a schematic diagram of a paintball marker including a control system according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring now to  FIG. 1 , a paintball marker  10  according to a first embodiment of the invention comprises a body  12  having a breech  14  and a barrel  16 , a paintball hopper  18  containing paintballs  19 , a bolt  20 , a compressed gas consister  22 , a firing mechanism typically in the form of an electronically actuated valve  24 , and a trigger  26 . 
   The hopper  18  opens into the breech  14  at a point of entry  15  adjacent the bolt  20  such that paintballs  19  can fall from the hopper  18  into the breech  14 , with the bolt  20  in its retracted position. A pressure sensor  30 , typically a piezo-electric pressure sensor or a strain gauge, is mounted in the breech  14  under the opening from the hopper  18  to the breech  14  and detects the presence of a paintball  19  in the breech  14 . The output from the sensor  30  is passed to a control unit  32 , typically a microprocessor, that is powered by a battery  34 . 
   The sensor  30  generates a differential output signal, i.e. a signal which varies with the rate of change of pressure on the sensor  30 . As shown in  FIG. 2 , an output  36  of the sensor  30  is connected to an analogue amplifier  38  that amplifies the output signal from the sensor  30 . The amplified signal is then passed to an analogue to digital converter (ADC)  40 . The ADC  40  is typically an 8-bit ADC giving 256 levels of digitisation. The digitised signal passes to the control unit  32 . 
   A user pulls the trigger  26 , effectively closing a switch  42  and sending an input to the control unit  32 . The control unit  32  monitors a timing cycle associated with the action of the bolt  20 , typically 14 ms per cycle of the bolt  20  and unless the control unit  32  has received an input signal corresponding to a paintball striking the sensor  30  prior to the trigger  26  being pulled, typically 0.05 s before, the timing cycle is interrupted and the control unit  32  limits the rate of actuation of the valve  24 . When the marker  10  is in an automatic or semi-automatic mode the control unit  32  monitors the output of the sensor  30  before each timing cycle whilst the trigger  26  is pulled. If the control unit  32  has not received an input signal corresponding to a paintball striking the sensor  30  prior to the start of the timing cycle the timing cycle is interrupted and the control unit  32  limits the rate of actuation of the valve  24 . 
   The rate of actuation of the valve  24  at a limited rate is set by the user, typically entering a value on a control panel  33 , typically using buttons  33   a,b , of the marker  10 . Typical limited rates of actuation of the valve  24  will be either zero, two or four shots per second. This reduces the chances of a paintball falling into the breech  14  and being chopped by the bolt  20  compared to the normal rate of actuation of the valve  24 , typically twenty times per second, by allowing more time for the paintball to fully enter the breech between shots. This reduced rate of fire of the marker  10  will continue until the sensor  30  is struck by a paintball whereupon the normal rate of fire is resumed. 
   Although shown in  FIG. 2  as being controlled by a solenoids  44  it will be appreciated that the valve  24  may be controlled by any suitable means, for example servo-motors or piezo-electric drivers. 
   As stated above the usual rate of fire of a paintball marker  10  when in automatic mode is typically twenty paintballs per second. However, the vibration signature of a paintball striking the sensor  30  and the action of the bolt  20  that are detected by the sensor  30  typically lasts for 0.09 seconds, almost twice the firing time of a paintball. 
   Referring now to  FIG. 3 , a portion of the signal corresponding to a paintball striking the sensor  30  has a very sharp peak region (A) that falls away rapidly to a second region (B) corresponding to the action of the bolt  20  and vibrations of the marker  10 . The peak region (A) has a magnitude that is typically twice that of the second region (B). A threshold (C) is set so as to exclude the second region (B) and a significant proportion of the peak region (A) from further signal processing. Although this thresholding can be carried out upon the analogue signal it is usual, and more convenient, to threshold the digitised signal as shown in FIG.  4 . This thresholding effectively reduces the lengths of the signal associated with a paintball striking the sensor so that only the first peak is detected and thus only a single peak per ball is registered by the control unit  32 . This therefore allows a rate of detection of up to twenty paintballs per second, this being the normal rate of fire of the marker  10 . 
   By setting the sensitivity threshold very low using the buttons  33   a,b  on the control panel  33 , it is possible to use the sensor  30  as a vibration sensor. This allows the sensor  30  to actuate an alarm  35  if the marker is moved by an unauthorised user, thus acting as a deterrent to theft. The alarm  35  may be an audible alarm. Alternatively, or additionally, the alarm may be a visual alarm, for example the LED  47  of FIG.  5 . Referring to  FIG. 5 , the marker  10  has a grip  45 , that incorporates the trigger  26 , upon which is located an LED  47  and a switch  49 . A user can toggle the control unit  32  off and on by using the switch  49 . Thus, the user can choose whether to reduce the risk of chopping of paintballs by having the control unit switched on, or not. The LED  47  is a visual indicator of whether the control unit  32  is activated. The LED  47  will typically be in a steady “on” state when the marker  10  is armed and the firing rate limiting function of the control unit  32  is not active and will flash when the firing rate limiting function of the control unit  32  is active. 
   Referring to  FIG. 6 , in a paintball marker according to a second embodiment of the invention many features correspond to those in the first embodiment, and are indicated by the same reference numeral increased by 100. The only significant difference is that the piezoelectric sensor  130  is not located in the breech  114 , but is located a short distance below it. A sensor rod  131  is supported in a vertical position with its upper end  131   a  projecting into the bottom of the breech  114  opposite the point of entry  115  of the paintballs  119  from the hopper  118 . The lower end  131   b  of the sensor rod  131  is in contact with a piezoelectric sensor  130 . The sensor rod  131  is supported so that it can move vertically to transmit forces, applied to its upper end  131   a  by the paintballs  119  entering the breech, to the sensor  130 . 
   It is possible to modify the operation of either of the embodiments described above, and one modification will now be described with reference to  FIGS. 1  to  5 . In this modification, if a trigger pull is registered by the control unit  32  it still checks whether a signal from the sensor  30 , indicative of the arrival of a paintball in the breach  114 , has been received since the last shot was fired. If it has, then the shot is fired immediately. If not, instead of varying the firing rate, the control unit  32  starts a delay for the one shot that has been requested by the trigger pull. Typically the delay might be for 35 ms. If within that 35 ms delay a signal is received from the sensor  30  indicating the arrival of a paintball  19  in the breech  14 , then the shot is immediately fired. If the delay period expires without the arrival of a paintball  19  in the breech  14  being detected, then the shot is fired anyway. There is therefore a maximum delay between the trigger pull and the firing of the shot, in this case of 35 ms, which will occur if no paintballs are sensed in the breech at all. 
   The advantage of this arrangement is that the marker will respond to each normal pull of the trigger by firing a shot within, at most, the delay period. This ensures that the player feels that the marker is responding to his pulling of the trigger. 
   The delay period can be adjusted using the buttons  33   a ,  33   b  on the marker grip. Decreasing the delay period will ensure that the marker fires more quickly for each trigger pull, but can increase the likelihood of chopping paintballs. Increasing the delay period reduces the likelihood of chopping paintballs, but can make the marker feel more as if it is not responding as quicker as the player might want. The delay period can be adjusted from 10 ms to 90 ms in 5 ms intervals. 
   It will be appreciated that the contact sensor can take a number of different forms, and can essentially comprise any sensor which senses contact with a paintball. As well as piezoelectric sensors or strain gauges, vibration sensors could be used, for example.