Patent Publication Number: US-11638989-B2

Title: Active safety sensing device and method for a fastner tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 119(e) of the filing date of U.S. Patent Application No. 62/908,261, which was filed on Sep. 30, 2019 and which is incorporated here by reference. 
    
    
     BACKGROUND 
     This specification relates to active safety devices and methods for fastening devices, such as nail guns. 
     According to the National Institute for Occupational Safety and Health (NIOSH), nail guns are responsible for about 37,000 emergency room visits each year. Various safety features exist such as interlocking pressure plates on the nose of the nail gun and sequential triggers. The plate restricts the user from firing into open air by requiring that contact is made with the workpiece. Unfortunately, both features are often misused or disabled. The pressure plate may be circumvented by holding down the trigger and allowing the nail gun to fire each time contact is made. This is sometimes referred to as “bump firing.” Sequential triggers restrict firing to a single nail for each pull of the trigger, but can also be disabled at the user&#39;s option. According to the Occupational Safety and Health Administration (OSHA), “2 out of 5 residential carpenter apprentices experienced a nail gun injury over a four-year period . . . . The risk of a nail gun injury is twice as high when using a multi-shot contact trigger as when using a single-shot sequential trigger nailer.” 
     SUMMARY 
     Embodiments of the present invention relates to the automatic detection of hazardous targets to inhibit the firing, or actively catch a fastener, such as a nail or screw, as it is exiting from a fastener driving tool. A two-part sensor system as well as a two-stage fastener driving system is utilized. The first part of the sensor system (part 1) may include a capacitive touch sensor on the nose guard of the driving tool. This sensor discriminates skin from wood, roofing material, etc., and locks out all driving functions while the hazard is detected. However, if the user accidentally makes contact with an area of the body that is covered by clothing (a glove for example), a second sensor (second part of the sensor system, part 2), which may also include a capacitive sensor, makes contact with the fastener and works in conjunction with stage 1) of the driving system to limit contact of the fastener with any area of the human body. 
     The two-part sensor system may be optimized by use of a neural network that has been trained on sensor data from the contact detection system to classify various types of materials including skin of a user. The two-part sensor system can thus distinguish more accurately skin from various materials and thereby provide more reliable system in distinguishing an active safety concern from proper use of the nail gun. 
     The driving system includes two stages, stage 1 and stage 2. Stage 1 of the driving system may be comprised of a continuously variable driver for testing the hardness and composition of the target material which also provides data to the pre-trained neural network to aide in classification of the material. 
     Stage 2 of the driving system may include a high-power driver for finishing the fastener into the material. During stage 1 of the driving operation, if a target is classified as hazardous, such as “no resistance” (driving into free air) is determined, stage 2 is locked out, the trigger is rendered inoperable, and the fastener is released from a firing readiness state. Similarly, if a hazardous target such as “human contact” is determined (via capacitive, ultrasonic, or RF sensing), stage 2 is locked out, the trigger is rendered inoperable, and the fastener is released from a firing readiness state. If, however, neither of the aforementioned hazardous targets are determined, the driving resistance is measured, the material is classified, and the finishing driving power for stage 2 is calculated based on the determined classification. Stage 2 of the driving operation is then allowed to continue and, by using the calculated driving power, accurately drives the fastener flush with the target material surface. During the driving operation of stage 2, if part 2 of the sensing system detects a hazardous target, a final high-speed catch system may be engaged. The high-speed catch system, in fractions of a millisecond, catches the nail as it is exiting the tool. 
     Therefore, safety is improved by avoiding hazardous unintentional firings. Additionally, performance is improved by more accurately driving the fastener. This also avoids fasteners being ejected through the target material and injuring others on the opposite side of the material. 
     The details of one or more embodiments of the subject matter of this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example of the two-part sensor system. 
         FIG.  2    illustrates an exemplary high-speed catch device. 
         FIG.  3    is an exemplary flow chart of the sensing, lockout and drive method 
         FIG.  4 A  illustrates an exemplary indicator. 
         FIG.  4 B  illustrates an exemplary indicator. 
         FIG.  5    is a flow chart illustrating the implementation of a processor. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The specification describes embodiments of the present invention of adaptive, active sensors and drivers for a fastener apparatus such as a nail gun. 
     Embodiments of the present invention are discussed in relation to a nail gun but may be utilized in any fastener device that includes projecting a fastener into material. The embodiments of the present invention include a two-part sensor system and a two-stage driving system. 
       FIG.  1    illustrates a two-part sensor system of the present invention. The two-part sensor system includes a direct contact sensor  110  that is placed external to the nail gun, such as a conductive plate or wire connected to the bumper plate, nose guard, or safety contact pressure plate on the nose of the tool. The direct contact sensor  110  may be a capacitive touch sensor or other equivalent technology which detects skin contact. The fastener  130  (nail, screw, etc.) itself may be conductive and may be used as a contact probe. This is accomplished with a secondary contact sensor  120 , which makes electrical contact with the fastener driver  160 , allowing electrical signals to flow from the fastener  130  through the fastener driver  160  and be measured by the processor  150 . When the fastener  130  is used as a probe, it is initially driven a short distance into the target material  140 , the cumulative force required to drive the given distance, the rate at which the drive was able to occur, and the change to the waveform of the electrical signal applied to the fastener are measured. This procedure constitutes stage 1. This measured information is provided to a processor  150  (later discussed) which performs calculations and controls the operation of the fastener driver  160  and safety mechanisms such as trigger Interlock  170  and any additional external processes such as user notifications. The distance that the probe should be driven in stage 1 may be predetermined and can be any distance that allows for the above measurements to be made. Some embodiments of the invention may utilize distances in the range of 1/10″-¼″. The drive pressure to drive the fastener  130  in stage 1 may be a constant drive pressure or pulse-width-modulated or any combination that allows for movement of the fastener  130  by the predetermined distance. For example, the fastener  130  may be percussively driven at a constant frequency with very low duty-cycle (pulse width) initially, then the duty-cycle (pulse width) is gradually increased until the fastener  130 , for example the nail head, has moved the predetermined distance. The method for this stage 1 driving procedure is described in more detail below. 
     Alternatively, an independent density/hardness sensor may be used separately and thus avoid direct contact with the fastener  130 . The independent density/hardness sensor may be located adjacent where the fastener  130  exits the fastener apparatus. The independent density/hardness sensor (not shown) may be comprised of a non-contact sensor such as an ultrasonic sensor, an RF sensor such as low-power radar, or a secondary physical contact sensor such as a dedicated probe or vibrometer. A classification of the composition of the target material including density, thickness, and hardness may be determined from the measurements obtained from the sensors in stage 1. Thus, from the classification of the composition of the target material, a determination is made of whether or not a hazardous condition exists—such as skin determined to be in the direct path of the fastener  130 —and action is taken to either stop the fastener movement or allow it to proceed. Traditional safety features remain in place, such as the mechanical safety catch, as well as the optional sequential trigger feature that only allows the nail gun to fire once for each pull of the trigger. 
       FIG.  1    further illustrates a two-stage driving system. Stage 1 is used in conjunction with a probe as discussed above. In stage 1 of the driving system, if the direct contact sensor  110  of the nail gun does not detect a hazardous target, such as skin, the fastener  130  is driven a short distance such as 1/10″-¼″ into the material. The stage 1 driver may be comprised of an electrical solenoid, electrical stepper or servo motor, or mechanical system such as a spring and plunger system, or pneumatic system comprised of a storage plenum  180  with rapid solenoid valve  185  as shown in  FIG.  1   . In stage 1 the composition of the target material is tested. This testing is a rapid operation, but slower than the stage 2 operation. 
     The stage 1 drive pressure may be linearly increased, or a given drive pressure may be pulsed at a variable duty-cycle (pulse width) in order to increase the drive pressure from zero to a predetermined value and measure the distance that the fastener  130  moved given the predetermined pressure. Alternatively, a predetermined drive distance may be set and the drive pressure is increased (up to the maximum pressure available) until the predetermined drive distance is achieved. The drive distance is measured by an encoder  190  placed adjacent to the secondary contact sensor  120 . Once the predetermined drive distance is achieved, the drive pressure is released. Depending on the given scenario, the peak drive pressure, pressure profile, drive distance, and/or time required to translate the fastener  130  a predetermined distance are stored in memory located in the processor  150 . An electrical signal (waveform) is induced onto the fastener  130  and the change in this signal over the drive distance is recorded in the memory. The signal provides information as to the electrical conductivity and change in capacitance as the fastener  130  travels into the material. This sensor data is retrieved from memory by a processor  150  and classification algorithms are performed to provide a determination of the composition of the target material  140 . The target material  140  may be determined to be skin, skin under clothing, wood, drywall, electrical wires, pipes, etc. A target is considered hazardous if its composition is determined to be any material or substance which, when driven in stage 2, would cause harm or would create an unsafe condition. Hazardous targets include but are not limited to: skin, free air (lack of target), target too soft, target too hard, electrical wire, conductive pipe, water, etc. 
     For a more precise classification of the target material  140 , the previously mentioned sensor data may be passed through a pre-trained neural network. A detailed description of the method of training, testing, and deploying the neural network is described later. The pre-trained neural network is trained with sensor data from fasteners  130  being driven into a variety of target materials  140 , both homogenous and inhomogeneous, including the aforementioned hazardous targets as well as standard targets such as wood, drywall, roofing material, etc. This training allows the neural network to differentiate between hazardous and non-hazardous targets, thus mitigating false alarms and misidentifications. 
     Based on the classification of stage 1 as well as the known properties of the fastener  130 , the finishing force required to drive the fastener  130  through completion of stage 2 is calculated. The calculated finishing force is then supplied by the stage 2 driving mechanism (described below) which then drives the fastener  130  through the target material  140 . 
     For example, if the force required in stage 1 to drive the fastener  130  over a given distance is measured to be below a predetermined safe threshold and also no change to the waveform on the fastener  130  is detected, it is assumed that the fastener  130  is being driven into open air and therefore stage 2 procedures are locked out. This prevents any energy (finishing force) which would have been supplied by the stage 2 driving mechanism from being released. Similarly, if the force required in stage 1 to drive the fastener  130  over a given distance is measured to be within predetermined safe thresholds but the waveform is perturbed in such a way as to indicate contact with a hazardous target such as skin, the trigger Interlock  170  are engaged and the trigger cannot be activated. However, if neither of these and/or other hazardous targets are determined, the finishing force required to drive the fastener  130  through completion of stage 2 is calculated and stage 2 is allowed to proceed. 
     Stage 2 of the driving system is comprised of a high-energy reservoir as well as an energy transfer instrument and a controller to drive the fastener  130  to its final position. The high-energy reservoir may be comprised of a pneumatic plenum  180  as shown in  FIG.  1    with compressed air. The energy transfer instrument for the stored compressed air energy may be comprised of a mechanically or electrically actuated solenoid valve  185  and the controller may be comprised of an electrical circuit which controls current to the electrically actuated valve and is enabled by a processor  150 . The high-energy reservoir may also include an electrical battery with a high-energy capacitor for rapid release of the battery&#39;s stored energy. The energy transfer instrument for the battery&#39;s and/or capacitor&#39;s energy may be comprised of a solenoid actuator and the controller may be comprised of an electrical circuit which controls current to the capacitor and/or solenoid and is enabled and/or modulated by a processor  150 . The high-energy reservoir may also be comprised of a large spring and plunger system that is coiled mechanically through an electric motor or other actuator. The energy transfer instrument for the spring&#39;s energy may be comprised of a mechanically or electrically actuated latch and the controller may be comprised of an electrical circuit which controls current to the latch and is enabled by a processor  150 . Alternatively, the high-energy reservoir may be comprised of a combustion chamber and a mixer such as a fan. The energy transfer instrument may be comprised of an ignition source such as a spark plug and the controller may be comprised of an electrical circuit controlling current to the ignition source and enabled by a processor  150 . 
     The necessary driving energy required to be transferred from the high-energy reservoir is calculated based on the finishing force which was calculated in stage 1. Assuming all safe conditions are met, a controlled release of the necessary driving energy is rapidly released via the energy transfer instrument, resulting in the fastener  130  being driven to the desired depth. Because the driving energy is calculated, the driving of the fastener  130  can be controlled to an intended depth. This allows for precision setting of the fastener  130 . Thus, if the fastener  130  is desired to be flush with the material, the required portion of the energy stored in the high-energy reservoir can be transferred such that the fastener  130  is driven flush with the target material  140 . Further, by using the calculated energy to control the firing, it eliminates any unintended firing of the fastener  130 . This includes firing the fastener  130  all the way through the material or setting the fastener  130  too far into the material where it may protrude partially through the material in an unintended manner. 
     During operation of the fastening apparatus, the sensing devices are being continuously monitored by the processor  150  for possible contact with skin or other hazardous target determination. In some circumstances a fastening apparatus may not initially be in contact with a hazardous target and ready to perform a stage 2 driving of the fastener  130 , however, one or more of the sensing devices discussed above may sense contact with a hazardous target during stage 2 operations. In an embodiment of the invention as disclosed in  FIG.  2   , a high-speed catch device  200  may be used to capture the fastener  130  should a hazardous target be determined during stage 2 of the driving procedure. The high-speed catch device  200  is located near the exit of the fastening apparatus as a last line of defense in preparation to apply an emergency-stop operation. The high-speed catch device is comprised of an electronic firing pin  240  which may be used to trigger the propellant  230  immediately upon hazardous target determination, which drives the impingement device  220  forward. The impingement device  220  then accelerates toward the smash plate  240  on the opposite side of the firing cavity, impacting the fastener  130  from the side and capturing the fastener  130 , halting its forward motion. Not shown is a release valve for removing the drive pressure on the fastener  130 , which may be triggered by the motion of the impingement device  220 . The chamber  260  for the firing cap can then be opened, for example opening the bolt  250 , to remove the spent cap and replace it with a new one. The system is reset by the opening of the chamber  260 . 
       FIG.  3    describes the hazardous target determination procedure. In step 1 ( 310 ), the direct contact sensor (part 1 of the sensor system) is continually measured to detect direct skin contact. If direct skin contact is detected, by the part 1 sensor then a hazardous target is immediately determined and the nail gun&#39;s safety features such as a trigger Interlock  350  are activated. If direct contact is not detected by the part 1 sensor, the system proceeds to step 2 ( 320 ). In step 2 ( 320 ), the variable drive process (stage 1 of the two-stage driving system) is initiated and variable drive pressure is utilized, along with the fastener  130  acting as a probe (part 2 of the two-part sensor). As previously described, if a hazardous target is determined, such as but not limited to open air or skin contact, then the nail gun&#39;s safety features/disabling device, such as a trigger Interlock  350  are activated and the system must be reset by releasing the trigger, which also removes pressure from the fastener  130  where the fastener  130  is in a non-firing state. 
     If no skin contact is detected, then the system proceeds to step 3 ( 330 ) which is stage 2 in the two-part driving system. In step 3 ( 330 ) the required energy to drive the fastener  130  to the desired depth is calculated by a processor and delivered via the energy transfer instrument such that the appropriate finishing force may be transferred to the fastener  130  to complete stage 2 for the given fastener  130  in the given target material  140 . 
     In step 4, if the appropriate target material  140  composition is determined and no hazardous targets are determined, then the calculated stage 2 finishing force is used to drive the fastener  130  into the material  140 . If during any part of step 4, a hazardous target is determined, then in an embodiment of the invention a high-speed catch device  200  may be employed such as discussed above with regard to  FIG.  2    to stop the forward motion of the fastener  130  or portions thereof. 
     Embodiments of the invention may include one or more user notification indicator features that indicate when a hazardous target is determined. For example,  FIG.  4 A  illustrates a capacitive sensor in the pressure plate of an electric nail gun. When this sensor is tripped by direct skin contact, firing is inhibited by electrically interrupting the signal from the trigger. Additionally, the hazardous situation (direct contact with skin in this case) is identified to a user by a red indicator LED  410  which is illuminated to warn the user. The nail gun cannot fire in this situation. In  FIG.  4 B , no hazardous target is determined (no direct skin contact) and the LED  410  is off. The nail gun functions as normal in this state. Any type of indicator that identifies when a hazardous target is determined may be used such as visual, acoustic, haptic, etc. 
       FIG.  5    describes the sensing, processing, and control system internal to the fastener apparatus for making all required calculations and generating the energy required to perform all operations. The input from all sensors is captured by the internal processor  150 . All data is stored in a memory device and processed by the internal processor  150  locally and in real-time. The interface to external components such as the control circuit for the electro-mechanical or pneumatic actuators is also controlled and monitored by the processor  150 . Safety critical actuators, such as any driving energy, are locked out by traditional mechanical systems such as the mechanical safety catch. The direct contact sensor  110  may also include a direct electrical lockout (not shown, but external to the processor  150 ) for redundancy and safety. 
     In embodiments where a neural network is use, the network must be pre-trained. The process of capturing data, training, and validating the neural network is repeated many times until the acceptable performance is obtained. Following validation, the network is optimized to fit and perform within the constraints of a small processor  150  located directly on or within the fastening apparatus. The optimized network is deployed to that device where real-time performance may be measured. 
     The purpose of the training data is to provide the neural network a very diverse set of data that is representative of a plurality of actual use scenarios. The network requires both the sensor input (each timestamp of sensor input) as well as annotation files with the correct classification which will become the network output. Having accurate annotations is crucial to a high-performing network as the difference between predicted network output and the values found in the annotation files determines the error function that is calculated and back-propagated through the network during training. Any error in the annotation file will adversely affect the performance of the network. 
     In embodiments of the present invention, the sensor input to the network may be comprised of time-series data, such as the electrical waveform induced onto the actual fastener  130  during stage 1 and stage 2 of the driving procedure, measured driving force over time, measured ultra-sonic sensor data, measured RF data, measured capacitive sensor data, temperature, humidity, inertial data, etc. For each timestamp in the sensor data stream, the appropriate material classification is recorded. 
     Data is collected while driving various fasteners  130  into a plurality of materials with different thickness, hardness, and density. Non-invasive testing, such as contact testing with a capacitive sensor may be performed on human test subjects, but tests which would perforate the skin in stage 1 or stage 2 will be performed on common human analog test subjects. 
     Once sufficient data has been captured and annotated, network training begins. The data is consolidated into a training set and test set. The training files are repeatedly fed to the neural network during training routines, while the test set is used exclusively for evaluating the performance of each training cycle. In this manner, the network is always evaluated using test data that it has never seen before. 
     During the training cycle, hyper-parameters are optimized such as learning rate, batch size, momentum, and weight decay. Additionally, several optimization methods may be explored to improve the accuracy of the network such as Stochastic Gradient Descent or Adam and/or other variants as best practices in training methods evolve. 
     Once satisfactory network performance has been achieved, a final evaluation step on real-world data is necessary to determine how well the network generalizes to new data, including new users and new user actions for the fastener driver. During this validation process, data is again collected and annotated for future training cycles to remove outliers in performance. 
     This training sequence is iteratively repeated to continually improve performance and add new test conditions and scenarios. 
     After training is complete, the network is frozen and optimized for efficient performance on an embedded device. This process may include quantizing the network, removing floating point operations and extraneous test and debug nodes. This improves performance on a resource-constrained device, such as a micro-controller, FPGA, or neural network accelerator. The frozen neural network is included when compiling the run-time executable, machine instructions, etc. Real-time data, as captured by the device, is then passed through the network during live operation of the tool, and real-time classifications of the material are made. 
     Although the present invention largely describes the implementation in a nail gun, the methods described could apply to drills and other cutting tools in a manner directed to their specific design. For example, the drill bit, rivet gun, die cutter, sewing needle or other perforating implements may act similarly as the fastener  130  and thus the embodiments of the invention implemented based on the specific design of each tool. 
     Embodiments of the subject matter and the functional operations described in this specification can be implemented in digital electronic circuitry, in tangibly-embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Embodiments of the subject matter described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible non transitory storage medium for execution by, or to control the operation of, data processing apparatus. The computer storage medium can be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of one or more of them. Alternatively, or in addition, the program instructions can be encoded on an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. 
     The term “data processing apparatus” refers to data processing hardware and encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can also be, or further include, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit). The apparatus can optionally include, in addition to hardware, code that creates an execution environment for computer programs, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. 
     Computers suitable for the execution of a computer program can be based on general or special purpose microprocessors or both, or any other kind of central processing unit. Generally, a central processing unit will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a central processing unit for performing or executing instructions and one or more memory devices for storing instructions and data. The central processing unit and the memory can be supplemented by, or incorporated in, special purpose logic circuitry. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more memory devices for storing data. However, a computer need not have such devices. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially be claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.