Patent Publication Number: US-2017370526-A1

Title: Device and a Method for Improving Safety in a Cutting Saw Apparatus

Description:
FIELD OF THE INVENTION 
     This invention relates to a device and a method for improving safety in a cutting saw apparatus. 
     BACKGROUND OF THE INVENTION 
     Cutting saw systems are commonly used for cutting materials like wood etc., Cutting saw systems usually comprise a saw or a cutting element in the form of a wheel which is held rotatably in the cutting saw system. The user moves the material to be cut towards the saw for the purposes of cutting. In doing so, there are chances of the user&#39;s hands coming into contact with the saw, which can prove to be disastrous and dangerous for the user. U.S. Pat. No. 5,510,685 discloses a safety mechanism for the user, integrated with the cutting saw system, which, upon detection of the user coming into contact with the saw, stops and retracts the saw into a cavity in the system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiments of this disclosure is explained in principle below with reference to the drawings. The drawings are: 
         FIG. 1  illustrates a schematic of a system for improving safety in a cutting saw apparatus; and 
         FIG. 2  illustrates a method for improving safety in a cutting saw apparatus 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a schematic of a system  5  for improving safety for a cutting saw apparatus. The system  5  comprises a device  10  for improving safety in a cutting saw apparatus. The system  5  is a part of the cutting saw apparatus, wherein the cutting saw apparatus comprises other components as well. The device  10  comprises a RC oscillation circuit  105  connected to a cutting saw  110 . The device  10  also comprises a detection module  115  connected to the RC oscillation circuit  105  to detect a change in an electrical output of the RC oscillation circuit  105  upon creation of a conductive path between the cutting saw  110  and a user  120 . The device  10  further comprises a control module  125  connected to the detection module  115  and a drive  130  of the cutting saw  110  for stopping the cutting saw, upon the detection module  115  detecting the change in the electrical output of the RC oscillation circuit  105 . The working of the device  10  will be described hereinafter. 
     The RC oscillation circuit  105  comprises a set of resistors, capacitors and an op-amp. In the RC oscillation circuit  105 , typical exemplary values of the bridge resistors can be 10 kΩ, the capacitors can be 1 nF and the voltage limiting resistor in the amplifier feedback loop can be 290 kΩ. As indicated, these are just exemplary values and the resistors and capacitors in the RC oscillation circuit  105  can take on different values as well. Different values of the resistors and capacitors provide different characteristics for the RC oscillation circuit  105 . The RC oscillation circuit  105  is an RC phase shift oscillator whose output frequency depends on the resistance connected in the feedback circuit and ground. 
     The detection module  115  comprises a signal processing circuitry, which processes and compares the input waveforms of the detection module  115  to detect any changes. 
     The system  5  further comprises a conductive layer  135  for supporting the user and basing a ground of the RC oscillation circuit  105 . In order to establish a conductive path between the cutting saw  110  and the user  120 , the user  120  has to wear a conductive footwear (not shown in Figures). The conductive footwear can be in the form of a conductive shoe or a removable base for the feet that is conductive. Similarly, a pair of hand gloves (not shown in Figures) with an internal metallic mesh lining, has to be worn by the user  120 . The purpose and working of the gloves will be described hereinafter. 
     The system  5  further comprises an insulator (not shown in Figures) disposed between the conductive layer  135  and earth, the purpose of which will be described hereinafter. 
       FIG. 2  illustrates a method  20  for improving safety in a cutting saw apparatus. The method  20  is carried out by the device  10  and comprises a first step  205  of detecting a change in an electrical output of the RC oscillation circuit  105 , by the detection module  115 , upon creation of a conductive path between the cutting saw  110  and the user  120 . The method  20  comprises a second step  210  of stopping the cutting saw  110  by controlling the drive  130  of the cutting saw  110  by the control module  125 . The working of the method  20  will be described hereinafter. 
     The purpose of the conductive footwear arranged to be worn by the user  120  is to form a conductive path between the user  120  and the conductive layer  135 . The conductive layer  135  connects the ground of the RC oscillation circuit  105  and the conductive footwear, thereby forming a conductive path between the RC oscillation circuit  105  and the user  120 , when wearing the conductive footwear. The purpose of the insulator is to insulate the conductive layer  135 , and more specifically the system  5  and the user  120 , from earth to improve the safety during any case of electrical leakage accidents, etc. 
     The purpose of the pair of hand gloves, if worn by the user, is to insulate and also protect the user from the cutting saw  110 . Usually, when the user  120  is cutting non-conducting materials like wood etc., the user  120  is naturally insulated from the cutting saw  110 . However, when the user  120  is cutting conducting or semi-conducting materials, the pair of hand gloves worn by the user  120  help in insulating the user  120  from the cutting saw  110 . But, by wearing the hand gloves when cutting conducting, non-conducting or semi-conducting materials, the user  120  is insulated from the cutting saw  110 . Hence, the technical advantage of using the pair of hand gloves is that it allows usage of the system  5  for conducting, semi-conducting and non-conducting materials. 
     The purpose of the internal metallic mesh lining of the pair of hand gloves is to physically protect the fingers or palm of the user when the cutting saw  110  accidentally comes into contact with an outer surface of the hand gloves and cuts the outer surface of the hand gloves. The other advantage of the metallic mesh lining is to include the user  120  in the RC oscillation circuit  105  to change the output characteristics of the circuit  105  to enable detection and stop the cutting saw  110  before the cutting saw  110  touches the fingers and palm of the user  120 , which will be explained hereinafter. 
     When the user  120  is cutting any type of material with the pair of hand gloves on, the user  120  will be insulated from the circuit  105  and the output of the RC oscillation circuit  105  as detected by the detection module  115  will be in line with the designed output characteristics of the circuit  105  in terms of the output signal waveform. This is because the user  120  is not included in the circuit  105 . When the cutting saw apparatus is being used, the detection module  115  will be constantly receiving the output from the circuit  105  and checking if the received waveform conforms to the designed output waveform within a specified tolerance level. Now, if the user  120  accidentally moves his hands close to the cutting saw  110  during cutting, the cutting saw  110  can abrade or cut the outer surface of the hand glove and make contact with either the internal metallic mesh liming, or in case the metallic lining is absent, the fingers or palm of the user  120  directly. Either of the above two cases can bring the user  120  in contact with the cutting saw  110 . The user  120  being a human and being conductive, therefore forms a conductive path between the cutting saw  110  and the conductive layer  135 . The user  120  is therefore included in the circuit  105  and the resistance characteristics of the circuit  105  changes, thereby consequently changing the electrical output and more specifically, the output signal waveform of the circuit  105 . To elaborate, inclusion of the human resistance of the user  120  can cause a change in the attenuation provided by a feedback circuit of the RC oscillation circuit  105 , resulting in a change in an amplitude of the electrical output of the RC oscillation circuit  105 . Examples of other changes of the electrical output of the RC oscillation circuit  105  can be a clipped sine wave of the output signal waveform, increased amplitude of the sine wave of the output signal waveform or a died out signal. 
     The detection module  115  which is continuously receiving the electrical output from the RC oscillation circuit  105  detects a change in the above mentioned electrical output, upon creation of the conductive path between the cutting saw  110  and the user  120 . In other words, the detection module  115  detects a change in the above mentioned electrical output, upon inclusion of the user  120  in the RC oscillation circuit  105 . To elaborate on the above, the signal processing circuitry of the detection module  115  receives, processes the electrical output or the output signal waveform of the RC oscillation circuit  105  and compares the same with a predefined or control signal waveform to detect the creation of the conductive path between the cutting  110  and the user  120  or the inclusion of the user  120  in the RC oscillation circuit  105 . 
     The above describes the step  205  of the method  20 . 
     The system  5  also comprises a power control module  140  for providing power to the RC oscillation circuit  105  and the cutting saw  110 . 
     Upon detection of the change in the electrical output of the RC oscillation circuit  105  by the detection module  115 , the detection module  115  communicates with the control module  125  or commands the control module  125  to stop the cutting saw  110 . Subsequently, the control module  125  controls the drive  130  of the cutting saw  110  to stop the cutting saw  110 . Additionally, the drive  130  can also retract the cutting saw  110  from a cutting position to provide improved protection to the user  120 . This is understood by the person of ordinary skill in the art. This describes the step  210  of the method  20 . 
     Large current and voltage levels cannot be used in the detection circuitry, due to the presence of the human as a user, due to obvious reasons. With the omnipresent nature of electrical noise in circuits and with low intensity current and voltage levels, detection of change in the signal output becomes less accurate, if there is a saw-human contact, thereby leading to disastrous effects for the user. The RC oscillation circuit  105  with reduced noise output characteristics is advantageous because it allows improved accuracy of detection with low intensity current and voltage levels in the circuit. 
     The system  5  can also learn the difference between ‘normal condition’ and ‘accident condition’ before the user  120  starts using the system  5 , which can be referred to as a learning routine. The ‘accident condition’ is a simulation of a saw-human contact scenario, wherein the cutting saw  110  comes into contact with the fingers of the palm of the user  120  or the internal metallic mesh lining of the hand gloves. To simulate the ‘normal condition’, the user  120  makes contact with a metallic element connected to the saw with the pair of hand gloves and the detection module  115  receives the output signal from the RC oscillation circuit  105 , the characteristics of which will be more or less the same as the designed characteristics of the output signal. To simulate the ‘accident condition’, the user  120  makes contact with a metallic element connected to the saw without the hand gloves and the detection module  115  receives the output signal from the RC oscillation circuit  105 , the characteristics of which will be quite different from the output signal in the ‘normal condition’. This information is saved in a suitable memory device in the system  5  and used under real-time conditions when actual detection is required. This enables the detection module  115  to learn the difference in the characteristics of the output signal waveform between ‘normal condition’ and ‘accident condition’. The resistance values of different human beings are different and therefore the bodies of different users can cause different changes in the output signal waveform. Hence, before a user starts using the cutting saw apparatus in which the system  5  is embodied, a learning routine as described above can be run to store the values. 
     It is to be understood that the foregoing description is intended to be purely illustrative of the principles of the disclosed techniques, rather than exhaustive thereof, and that changes and variations will be apparent to those skilled in the art, and that the present invention is not intended to be limited other than as expressly set forth in the following claims.