Patent Publication Number: US-2017348835-A1

Title: Electric torque tool with ramping effect

Description:
BACKGROUND 
     There are various methods and devices for controlling torque provided by a powered tool for tightening a fastener. 
     SUMMARY 
     Many existing methods and devices for controlling a torque tool to apply a desired amount of torque to a threaded fastener are imprecise. Few if any of such methods and devices reduce the likelihood of applying excessive torque to a threaded fastener. In one embodiment, the invention avoids overshoot of torque when a fastener completes threading and the fastener suddenly contacts the surface of a bolt, flange or other receiving element. If not controlled, such contact causes a sudden spike or increase in torque output by a tool beyond the ratings for the tool and/or the fastener. 
     One embodiment provides a method for applying torque for securing a fastener with a torque tool. The method includes determining an initial command torque value for outputting torque to a fastener engaged by the torque tool that is less than a target command torque value and, in response to actuation of the torque tool, operating the torque tool at the initial command torque value. The method further includes, in response to a spike in torque, increasing from the initial command torque value to a jump command torque value to increase torque output by the torque tool, and ramping from the jump command torque value toward the target command torque value to increase torque output by the torque tool. 
     Another embodiment provides an electric torque fastening system. The system includes a torque tool including an actuator, an electric motor and a motor speed sensor, and a controller for controlling power to the electric motor. The controller is configured to, upon actuation of the torque tool by the actuator, provide an initial command torque value for providing power to the electric motor to apply torque to a fastener engaged with the torque tool. In response to a spike in torque, the controller is configured to provide a jump command torque value that is greater than the initial command torque value to increase electrical power to the electric motor and increase torque output by the torque tool, and to subsequently provide a ramping increase from the jump command torque value toward a target command torque value to increase the electrical power provided to the electric motor and thus the torque output by the torque tool. 
     Another embodiment provides a method for applying torque for securing a fastener with a torque tool. The method includes, in response to a target torque value, determining an initial command torque value, a jump command torque value, and a target command torque value. In response to actuation of the torque tool, the method operates the torque tool at the initial command torque value and, in response to a spike in torque, essentially instantaneously increases from the initial command torque value to the jump command torque value to increase torque output by the torque tool. Thereafter, the method ramps from the jump command torque value toward the target command torque value to increase torque output by the torque tool. 
     Other aspects and embodiments will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a torque tool according to one embodiment. 
         FIG. 2  is a rear view of the torque tool that includes a control panel. 
         FIG. 3  is a perspective view of a torque fastening system that includes the torque tool. 
         FIG. 4  is a block diagram of the torque fastening system. 
         FIG. 5  is a flow chart of a ramping routine for the torque fastening system. 
         FIG. 6  is a graph showing one example of an operation of the ramping routine. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     As should also be apparent to one of ordinary skill in the art, the systems shown in the figures are models of what actual systems might be like. Many of the modules and logical structures described are capable of being implemented in software executed by a microprocessor or a similar device or of being implemented in hardware using a variety of components including, for example, application specific integrated circuits (“ASICs”). Terms like “processor” and “controller” may include or refer to both hardware and/or software. The term “memory” may include or refer to volatile memory, non-volatile memory, or a combination thereof and, in various constructions, may also store operating system software, applications/instructions data, and combinations thereof. 
       FIG. 1  illustrates an example of a torque tool  20 . The torque tool  20  includes a body  22 , a hand grip  24  and an actuator  26 , such as a trigger. The torque tool  20  includes a fastener receiver  30  shaped to receive an adaptor and engage a threaded fastener. The torque tool  20  has a reaction arm  32  disposed at a front end so a user can maintain the position in use. The torque tool  20  includes a planetary torque gearbox disposed within a front housing  34  that provides torque generated by an electric motor disposed within the torque tool to rotate the fastener receiver  30 . 
       FIG. 2  shows a torque tool control panel  40  having a display  42  (for example, an LED display) that is disposed at a rear end of the torque tool  20 . Push buttons  44 - 47  (for example, pressure sensing switches) on the torque tool control panel  40  receive user inputs and provide visual confirmation for the inputs and conditions of the torque tool  20 . The push buttons  44 ,  45  act as up down buttons in some setting operations. In other embodiments, other input devices may be used, for example, icons on a touch screen. The actuator  26  acts as an input for setting a mode or condition in some situations. 
       FIG. 3  shows an electric torque fastening system  50  that includes the torque tool  20 . In the example illustrated, the electric torque fastening system  50  includes a power connecting jack  52  and a communication connecting jack  54 , that are each connected to a lower end of the hand grip  24  of the torque tool  20 . The power connecting jack  52  electrically connects a power connector  56  to the torque tool  20 . The communication connecting jack  54  electrically connects a communication connector  60  to the torque tool  20 . A second end of the power connector  56  includes a power jack  62  and a second end of the communication connector  60  includes a communication jack  66 . A control unit  70  includes ports that receive the power jack  62  and the communication jack  66 . The control unit  70  includes a control unit input interface/display  74  (for example a touchscreen) for receiving inputs from a user and displaying information. A connector sheath  80  protects the power connector  56  and the communication connector  60  by acting as a single cable for the connectors  56 ,  60 . 
       FIG. 4  is a block diagram  84  of the components of the electric torque fastening system  50 . The components of the torque tool  20  include the torque tool control panel  40 , a processor  86  provided with a circuit board, a motor speed sensor  88  (for example an encoder) and an electric motor  90 . The torque tool  20  includes a power port  92  and a communication port  94  disposed in the outer end of the hand grip  24  that receive the power connecting jack  52  and the communication connecting jack  54 , respectively. 
     Components of the control unit  70  shown in  FIG. 4  include the control unit input interface/display  74 , a controller  100  that includes a memory  102 , a servo drive  104 , and an AC/DC power convertor  110 . Further, the control unit  70  includes a power port  112  that receives the power jack  62  and a communication port  116  that receives the communication jack  66 . Further, a port  118  (for example, a USB port) is provided for downloading or uploading data to and from memory  102  to and from external devices. Finally, an outlet connector  120  is provided for connecting the AC/DC power convertor  110  of the control unit  70  to a power source, such as a wall outlet. The AC/DC power convertor  110  converts AC power to DC power. 
     Set-Up 
     In the example illustrated, depending on the capabilities of a torque tool  20  and a control unit  70 , a gear box selection is made by a user or operator that utilizes the push buttons  44 - 47  to select between 1000, 2000, 3000 and 6000 maximum foot-pounds for the torque tool. Further, a user also selects between a 115 volt and a 230 volt external power supply for the electric torque fastening system  50 . The controller  100  of the control unit  70  is programmable and configured to store the inputs in memory  102  and utilize the inputs to prepare the electric torque fastening system  50  for operation. Thus, the capabilities or operating values for the specific torque tool  20  and the corresponding control unit  70  are set. The capabilities are set forth in a table of values for a specific torque tool having the selected gear box and the specific power supply. For example, a program or routine for providing look up tables of the specific torques, power supply values, and gear boxes is downloaded to memory  102  of the electric torque fastening system  50 . The selections of the gear box and the external power supply value result in a selection of specific tables for the specific torque tool  20 . Upon this programming, the torque tool  20  is now configured to operate with the maximum torque value and the power supply voltage as selected. Thus, inputs selecting the gearbox or the power supply no longer occur as the electric torque fastening system  50  has been set. 
     Initially a user inputs a target torque value and angle of rotation or turn for one or a group of fasteners using one of the torque tool control panel  40  and the control unit input interface/display  74 . For instance, a user may enter or select a desired target torque value, angle of rotation, and number of fasteners to be secured into the torque tool control panel  40  of the torque tool  20 . Alternatively, the information is entered into the control unit input interface/display  74  of the control unit  70 . The controller  100  of the control unit  70  processes the inputs. The target torque value corresponds to a target command torque value determined by the controller  100  to provide to the servo drive  104 . The controller  100  also is configured to store in memory  102  various percentages of the command target torque value to apply at start-up of the torque fastening system. Further, values for a jump or increase in torque in response to a torque spike are calculated, predetermined and/or pre-stored for a given target torque value. Further, the amount of increase in ramping over time from the jump command torque value to obtain the target command torque value is also stored. Thus, for various torque tools, fasteners and usage, values for a selected target torque applied to a fastener are preset or otherwise stored. 
     More specifically, a target command torque value, a jump command torque value, an initial command torque value, and a ramp speed are determined based on gearbox size, the target torque value input by an operator, and the power supply value (115 or 230 volts) for the electric torque fastening system  50 . The selected lookup table is used to define the ramp speed and other values. The lookup tables have five torque set-points (20%, 40%, 60%, 80% and 100% of full load) The ramping rate or ramping speed is determined from interpolation. The initial command torque value is not less than a minimum value regardless of the inputs. 
     The torque tool control panel  40  and the control unit input interface/display  74  also are also both operable to selectively change the direction of rotation of the fastener receiver  30  and perform other operations, such as downloading information from the port  118 . 
     After, the electric torque fastening system  50  is programmed or otherwise set-up to operate, when the actuator  26  of the torque tool  20  is actuated to tighten a fastener, operation of a routine or program for securing a fastener begins. 
     Operation 
       FIG. 5  is a flowchart of an exemplary routine  200  or program for the controller  100  to execute a power ramping algorithm to secure a fastener upon actuation of the actuator  26 . Upon actuation, the communication connector  60  transmits an actuation signal, and in some instances other communication signals, between the processor  86  of the torque tool  20  and the controller  100  of the control unit  70 . 
     Initially, the controller  100  is configured to provide an initial command torque value to the servo drive  104 , which provides electrical power to the electric motor  90  to provide a corresponding torque value to a fastener (step  202 ) shown in  FIG. 5 . The initial command torque value (for example 20% of full load) is preselected or determined to achieve a maximum speed of rotation for the fastener receiver  30  under low torque/load conditions and to avoid an output of excessive torque when the load provided by the fastener increases. The controller  100  of the control unit  70  is configured to receive a motor speed value from the motor speed sensor  88  of the torque tool  20  (step  204 ) transmitted via the processor  86  and the communication connector  60 . 
     More specifically, in the example illustrated (step  204 ), the motor speed sensor  88  is an encoder. The motor speed is provided by the rate over time of output pulses from the encoder. The controller  100  is configured to analyze the pulses output by the encoder (processor  86  in an alternative arrangement). Every time a pulse is detected the time difference from the previous pulse (microseconds) is stored in an array in the memory  102 . One hundred time values are stored. When a new pulse is received and stored, the oldest stored time value is erased. The controller saves the last four encoder readings and evaluates the difference in time between the current pulse and the prior pulse. The controller  100  calculates the average of the last four differences. Thus, the arrangement requires at least seven encoder readings after an actuation of the actuator  26  to have a stable output. Successive time differences are compared. As long as the time differences are decreasing, increasing speed is determined. Once at least five consecutive new time readings (for example, ten new time readings) are greater than the previous readings, a slowing speed is determined. Thereafter two additional options are determined as follows to result in a slowing speed. If at least one from the group consisting of 1) the speed difference or decrement is equal to more than 1 second, and 2) the speed decrement detected is 50% or less from the maximum speed recorded (minimum time between pulses), the controller  100  advances to increase the torque output (step  212 ). 
     So long as the speed does not decrease, the routine maintains the supply of electrical power and again determines the motor speed (step  204 ). When the controller  100  determines the decrease in motor speed (step  208 ), the routine increases the output of the controller  100  to provide a jump command torque value (step  212 ) to the servo drive  104 , which provides a corresponding electrical power value (for example 50% of full load) to the electric motor  90 . 
     As shown in  FIG. 5 , subsequent to the increase to the jump command torque value, the controller  100  is configured to increase the command torque value from the jump command torque value by incrementally increasing or ramping the command torque value toward the target command torque value over time (step  216 ) as shown in  FIG. 5 . The controller  100  is configured to then compare the increased command torque value with the target command torque value (step  218 ). If the target command torque value is not met, the routine returns and increases the command torque value (step  216 ). When the target command torque value is met (step  218 ), the routine advances and the controller  100  is configured to maintain the target command torque value to the servo drive  104  for a predetermined time when no rotational movement of the fastener receiver  30  is detected (step  220 ). Thereafter, the controller  100  discontinues an output to the servo drive  104 , which ends the supply of power to the electric motor  90  (step  224 ), and thus ends operation of the torque tool  20 . 
     In one embodiment, the controller  100  is configured to then indicate a status of the fastener (step  228 ). The status of a fastener includes whether the proper torque value was applied to the fastener for the proper time without movement of the fastener receiver  30 . Thus, a pass/fail indication is provided and stored for the condition of a mounted fastener. 
     In an instance wherein the actuator  26  is actuated, but the tool does not move enough to detect a speed decrement or decrease (fastener already tightened), after a predetermined time the controller  100  will advance the routine to the jump command torque value and ramp the command torque value. 
     Example 
       FIG. 6  is a graph with three graph sections that illustrate an example of one method of applying torque with the torque tool  20  to a fastener in accordance with the embodiment of  FIG. 5 . As shown in  FIG. 6 , the lowest graph section shows motor speed (revolutions per minute RPMs) over time for the torque tool  20 . The middle graph section shows a command torque value in millivolts (mV) over time provided to a servo drive  104 . The upper graph section shows torque (ft-lbs) over time for the torque tool  20 . 
     As shown in  FIG. 6 , at time A (0.0 seconds), the electric torque fastening system  50  is powered up. At time B, the actuator  26  is triggered by a user and an initial command torque value (mV) is provided by the controller  100  to the servo drive  104  as shown in the middle graph section of  FIG. 6 . Based on the start-up command torque value, the servo drive  104  controls the electrical power received from the AC/DC power convertor  110 , that is provided to the electric motor  90 . In  FIG. 6 , during most of the time period B-C, motor speed increases rapidly as, for instance, the torque tool  20  rotatably advances a threaded fastener onto a bolt or the like. 
     At time C shown in  FIG. 6 , the threaded fastener begins seating on the face of a bolt. As the fastener seats onto the bolt, further rotation is very limited. Thus, the motor speed falls rapidly at or about the time C as shown in the lower graph section of  FIG. 6 . The decrease in motor speed (step  208  in  FIG. 5 ) corresponds with an increase in output torque as shown by a spike or large increase in torque as shown in the upper graph section, that occurs concurrently with the decrease in motor speed as shown in the lower graph section of  FIG. 6 . Thus, the motor speed decrease is a different variable that corresponds with the torque increase. Therefore, sensing the motor speed decrease replaces the need for a torque sensor. 
     As shown in  FIG. 6  at time C, in response to the decrease in motor speed, and thus the concurrent increase in torque, the controller  100  provides a jump command torque value (mV) to the servo drive  104 . The jump command torque value is much greater than the initial command torque value. As shown in the middle graph section of  FIG. 6 , the increase from the initial command torque value to the jump command torque value is an essentially instantaneous increase in the command torque value provided by the controller  100  to the servo drive  104 . Thus, the servo drive  104  is configured to receive the jump command torque value from the controller  100  and provide corresponding increased electrical power to the electric motor  90 . 
     Thereafter, as shown in the middle graph of  FIG. 6 , the command torque value provided to the servo drive  104  is ramped. Consequently, the electrical power provided to the electric motor  90  is increased over time. Ramping of the command torque value generally corresponds to ramping of the torque value provided to a fastener as shown in the upper graph of  FIG. 6 . 
     As shown at time D in  FIG. 6 , the ramped command torque value equals the target command torque value for the particular torque tool  20  and corresponds to the particular torque desired for the particular fastener being mounted. Thus, at time D, the ramping of the command torque value ends, and the target command torque value is applied to the servo drive  104  until a predetermined or preselected time E, with no movement of the fastener receiver  30  of the torque tool  20  occurring. At time E, the target command torque value is deselected by the controller  100 , and thus electrical power is no longer output to the electric motor  90  by the servo drive  104 . The time segment D-E is determined or preselected to obtain a particular resultant torque value for a set time or portion of a set time, to obtain a properly secured fastener. 
     By applying an initial command torque value that is less than the target command torque value, a severe spike in torque output by the torque tool  20  onto a fastener that is greater than the target torque value for the system is avoided at time C as shown in  FIG. 6 . Instead, the spike in torque value remains less than the target torque value for the fastener. Further, the initial command torque value limits operation of the electric motor  90  to a maximum speed that is appropriate for the electric motor. This arrangement is an advantage over other fastening systems, wherein the torque value spikes to a magnitude that may cause damage to a fastener or even to the torque tool  20 . Further, such a spike in torque may result in a poorly joined fastener. Jumping to a jump command torque value, that is less than the target command torque value, also ensures that the torque applied by the torque tool  20  does not exceed the desired torque value for the particular fastener. 
     In one embodiment, the controller  100  is configured for discontinuing the target command torque value so long as rotation of a threaded fastener or movement of the drive of the electric motor  90  does not occur during at least a portion of a set amount of time. 
     In one embodiment, the ramping from the jump command torque value and toward the target command torque value includes increasing a voltage from the controller  100  to the servo drive  104 , such that the servo drive provides electrical power to the electric motor  90  to increase the torque at a rate of between about 100 foot-pounds/second and about 1000 foot-pounds/second. 
     In one embodiment, the controller  100  is a servo controller for an open-loop servo-control system. In another embodiment, the controller  100  is a servo controller for a closed-loop servo-control system. In another embodiment, the controller  100  is a servo controller for a cascaded servo-control system, which uses velocity as an inner loop control and torque as an outer loop control. 
     In one embodiment, the servo drive  104  provides pulse width modulation (PWM) to the electric motor  90 . The servo drive  104  increases pulse width to increase the electrical power provided to the electric motor  90 . Other arrangements are contemplated. 
     In one embodiment, the initial command torque value is ramped or changes in power value, such as by increasing in magnitude over time. The torque tool  20  operates as a torque wrench in one embodiment. 
     In one embodiment, the power connecting jack  52 , the power jack  62  and the power connector  56 , along with the communication connecting jack  54 , the communication jack  66  and the communication connector  60 , are replaced by a single coaxial cable having individual connecting jacks on respective ends thereof. The coaxial cable provides power and communication signals from the control unit  70  to the torque tool  20 . 
     In another embodiment, the elements of the control unit  70 , including the AC/DC power convertor  110 , are integrated into the body  22  of the torque tool  20 . Thus, the separate control unit  70  is eliminated. 
     In one embodiment, the electric torque fastening system  50  is free from a torque sensor for directly sensing or directly measuring torque output by the torque tool  20 . Thus, a measured torque value is not necessary or provided to control the torque for the electric torque fastening system  50 . 
     In another embodiment, the torque tool  20  of the electric torque fastening system  50  includes a torque sensor (not shown). The torque sensor is a strain-gauge or other sensor provided with the torque tool  20 . Turning to the flow chart of  FIG. 5 , in this embodiment, torque is determined by a torque sensor (step  204  modification), instead of motor speed. A torque spike is determined (step  208  modification) based on the spike in directly measured torque value. Further, in this embodiment, a target torque value is compared with the actual measured torque value (step  218  modification) and the target torque value is maintained by direct measurement of the torque value and control of power to the electric motor  90 . Thus, direct measurement of torque ensures accurate operation of the electric torque fastening system  50 . In this embodiment, the target command torque value is adjustable based on the measured torque value. 
     In another example, the motor speed sensor  88  is a Hall effect sensor. 
     Thus, embodiments provide, among other things, an arrangement for controlling a torque tool  20  to apply a preset value of torque to a fastener by limiting electrical power applied to an electric motor of the torque tool initially, and eventually ramping the electrical power and thus ramping or increasing the torque applied by the torque tool. Various features and advantages of the invention are set forth in the following claims.