Powered screwdriver including clutch setting sensor

Abstract

To solve problems with the prior art.SOLUTION: A rotary power tool includes a gear case, an output shaft extending from the gear case, and a drive mechanism configured to provide torque to the output shaft to rotate the output shaft. The rotary power tool further includes a clutch mechanism between the output shaft and the drive mechanism. The clutch mechanism includes a compression spring and is configured to limit the amount of torque provided by the output shaft. The rotary power tool further includes a sensor positioned on a neck portion of the gear case subject to strain imparted by the compression spring, and an electronic control unit configured to receive an output signal from the strain gauge and determine a torque setting of the clutch mechanism based on the output signal.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to co-pending U.S. Provisional Patent Application No. 63 / 063,737, filed August 10, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates generally to power tools, and more particularly to power drivers. [Background technology]

[0003] Power drivers are used to tighten and torque fasteners, etc. Some power drivers include a clutch mechanism that allows the user to limit the torque applied to a fastener. Summary of the Invention [Means for solving the problem]

[0004] In one aspect, the present invention provides a rotary power tool comprising a gear case, an output shaft extending from the gear case, and a drive mechanism configured to provide torque to the output shaft to rotate the output shaft. The rotary power tool further comprises a clutch mechanism between the output shaft and the drive mechanism. The clutch mechanism comprises a compression spring and is configured to limit the amount of torque provided by the output shaft. The rotary power tool further comprises a sensor disposed in a neck portion of the gear case that is subjected to strain imparted by the compression spring, and an electronic control unit configured to receive an output signal from the strain gauge and determine a torque setting for the clutch mechanism based on the output signal.

[0005] In another aspect, the present invention provides a rotary power tool comprising a gear case, an output shaft extending from the gear case, and a drive mechanism configured to provide torque to the output shaft to rotate the output shaft. The rotary power tool further comprises a clutch mechanism between the output shaft and the drive mechanism. The clutch mechanism comprises a compression spring and is configured to limit the amount of torque provided by the output shaft. The rotary power tool further comprises an inductive sensor proximate to the compression spring such that a voltage is induced in the inductive sensor in response to relative motion between the compression spring and a magnetic field emitted by the inductive sensor. The rotary power tool further comprises an electronic control unit configured to receive an output signal from the inductive sensor indicative of a change in inductance in the inductive sensor and determine a torque setting for the clutch mechanism based on the output signal.

[0006] In another aspect, the present invention provides a rotary power tool comprising a gear case, an output shaft extending from the gear case, and a drive mechanism configured to provide torque to the output shaft to rotate the output shaft. The rotary power tool further comprises a clutch mechanism between the output shaft and the drive mechanism. The clutch mechanism comprises a compression spring and is configured to limit the amount of torque provided by the output shaft. The rotary power tool further comprises a clutch adjustment assembly configured to adjust a compressed length of the compression spring. The rotary power tool further comprises a lockout mechanism adjustable between a locked state in which the clutch adjustment assembly is prevented from adjusting the compressed length of the compression spring, and a released state in which the clutch adjustment assembly is allowed to adjust the compressed length of the compression spring.

[0007] Other features and aspects of the present invention will become apparent from consideration of the following detailed description and accompanying drawings. [Brief description of the drawings]

[0008] [Figure 1] 1 is a front perspective view of a power screwdriver according to an embodiment of the present invention; [Diagram 2]2 is a cross-sectional view of the power screwdriver of FIG. 1 taken along line 2-2, showing the clutch mechanism in a low torque setting. [Diagram 3] 2 is a cross-sectional view of the power screwdriver of FIG. 1 taken along line 2-2, showing the clutch mechanism in a high torque setting. [Figure 4] FIG. 2 is a detailed view of the power screwdriver with a portion of the housing removed, showing a partially exploded view of the clutch mechanism. [Diagram 5] 1 is an exploded perspective view of a portion of a power screwdriver showing a drive mechanism and a clutch mechanism. [Figure 6] 6 is a cross-sectional view of the power screwdriver of FIG. 4 taken along line 6-6, showing a portion of the clutch mechanism. [Figure 7] 1 is a detailed view of the power screwdriver with a portion of the housing removed, showing a portion of the clutch mechanism. FIG. [Figure 8] FIG. 2 is an exploded perspective view of the electric screwdriver, showing a main clutch sensor of the clutch mechanism. [Figure 9] 4 is a graph showing a signal output from a main clutch sensor of the amount of strain applied to a gear case as the clutch mechanism transitions between various torque settings. [Figure 10] FIG. 13 is a plan view of an alternative embodiment of the main clutch sensor showing the clutch spring of the clutch mechanism at a low torque setting. [Figure 11] FIG. 11 is a plan view of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism at a variable torque setting between a low torque setting and a high torque setting. [Figure 12] FIG. 11 is a top view of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism in a high torque setting. [Figure 13] 4 is a graph showing the ratio of coil density to length of the clutch spring as the clutch mechanism transitions between low and high torque settings. [Figure 14] FIG. 11 is a plan view of the alternative embodiment of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism at a low torque setting. [Figure 15]FIG. 11 is a plan view of another alternative embodiment of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism at a low torque setting. [Figure 16] FIG. 11 is a plan view of yet another alternative embodiment of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism at a low torque setting. [Figure 17] FIG. 11 is a plan view of yet another alternative embodiment of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism at a low torque setting. [Figure 18] FIG. 11 is a plan view of yet another alternative embodiment of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism at a low torque setting. [Figure 19] FIG. 11 is a plan view of yet another alternative embodiment of the main clutch sensor of FIG. 10 showing the clutch spring of the clutch mechanism at a low torque setting. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Before describing any embodiment of the invention 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 carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0010] FIG. 1 illustrates a power tool 10 (e.g., a power screwdriver) that includes a housing 14, an electric motor (e.g., a brushless electric motor 18, FIG. 2) disposed within the housing 14, and an output shaft 22 that performs work directly or indirectly on a workpiece during operation of the tool 10. The power tool 10 applies a precise amount of torque to a workpiece without over-clamping (i.e., over-torquing) the workpiece. The power tool 10 is powered by a battery pack 26. In other embodiments, the power tool 10 is powered using a power cord that is connected to a power source (e.g., a wall outlet). Additionally, while the power tool 10 in the illustrated embodiment is a non-impact rotary tool, in other embodiments, the power tool may alternatively be an impact rotary tool.

[0011] With continued reference to FIG. 1 , the output shaft 22 includes a hex socket 30 for receiving a tool bit (not shown) that can engage with a workpiece (e.g., a fastener). In other embodiments, the output shaft 22 may include a different configuration, and the power tool 10 may include a conventional chuck for receiving any number of different tools. The power tool 10 further includes a handle 34 and a gear case 38 coupled to the housing 14. The output shaft 22 extends beyond the gear case 38. The handle 34 is shaped to allow a user to easily grasp and operate the tool 10 via a trigger switch 40. A battery pack 26 connects to the handle 34 and selectively provides power to the motor 18 to drive a drive mechanism 42 of the power tool 10. In the illustrated embodiment, the battery pack 26 is partially insertable into the handle 34.

[0012] 2 and 3, the torque applied by the power tool 10 is adjustable. Depending on the application, a user can adjust the torque setting of the power tool 10 to apply different and precise amounts of torque. In the illustrated embodiment, the user selects either a first (or low) torque setting as shown in FIG 2, a second (or high) torque setting as shown in FIG 3, or any level of torque between the low and high torque settings.

[0013] 2 and 3, the drive mechanism 42 includes a transmission 44 that is at least partially disposed within the gear case 38. The transmission 44 includes a first stage gearset 50, a second stage gearset 52, and a third stage gearset 54. In the illustrated embodiment, the third stage gearset 54 includes an output carrier 56 that rotates relative to the gear case 38 and planetary gears 58 rotatably supported on the output carrier 56. The output carrier 56 is driven or rotated by the motor 18 of the power tool 10 via the first stage gearset 50 and the second stage gearset 52.

[0014] The output shaft 22 is coupled to the output carrier 56 and rotates in response to rotation of the output carrier 56. In the illustrated embodiment, a drive bearing 62 is circumferentially disposed about the output shaft 22. The drive bearing 62 is disposed between the output shaft 22 and the gear case 38 to rotatably support the output shaft 22 relative to the gear case 38.

[0015] 2 and 3, the power tool 10 further includes a clutch mechanism 66 and a clutch adjustment assembly 68. The clutch mechanism 66 operates between a first, low torque setting (FIG. 2) and a second, high torque setting (FIG. 3). During the low torque setting, the clutch mechanism 66 delivers a precise, low torque to the output shaft 22. During the high torque setting, the clutch mechanism 66 delivers a precise, high torque to the output shaft 22. The clutch mechanism 66 is also capable of operating at variable torque settings between the low and high torque settings to deliver respective precise torques.

[0016] The clutch adjustment assembly 68 includes a collar 70 and a nut 74 co-rotatably coupled to the collar 70 but not axially fixed thereto, as shown in FIGS. 2 and 3. The clutch mechanism 66 includes a clutch spring 78 and a pair of spring end plates 82, 86 disposed at either end of the clutch spring 78. The illustrated clutch spring 78 is a compression spring, although in other embodiments, different springs may alternatively be used, such as disc springs, conical coil springs, or wave springs. Also, while the illustrated clutch spring 78 coils include a circular cross-sectional shape, in other embodiments, the clutch spring 78 may alternatively have a square cross-sectional shape. The clutch spring 78 is disposed about the output shaft 22 and compressed between the spring end plates 82, 86. Specifically, the clutch spring 78 includes a first end 88 (FIG. 5) that abuts the end plate 82 and a second end 90 that abuts the end plate 86. The clutch spring 78 has a relatively low stiffness to provide fine adjustment of the compression force through the clutch mechanism 66 .

[0017] The collar 70 is circumferentially disposed around the neck portion 91 of the gear case 38. The nut 74 is hexagonal and rotatably coupled to the collar 70. In other embodiments, the nut 74 may be splined to the collar 70. The nut 74 is also threadedly coupled to the neck portion 91 of the gear case 38. Thus, the nut 74 is axially movable relative to the collar 70 and the gear case 38. Specifically, the nut 74 includes internal threads 92 (FIG. 5) that engage with external threads 94 (FIG. 5) on the gear case 38, such that the nut 74 is rotatable relative to the gear case 38 and translatable along the neck portion 91. The nut 74 is axially movable along the neck portion 91 of the gear case 38 between a low torque setting (FIG. 2) and a high torque setting (FIG. 3). In some embodiments, the threads 94 may be of fine helical pitch to allow finer adjustment of the compression force of the clutch mechanism 66. Nut 74 includes a number of detents 95 that interface with ridges 96 on spring end plate 82 (FIG. 4). As nut 74 rotates relative to spring end plate 82, ridges 96 slide and ride up adjacent detents 95, providing tactile feedback as the user rotates collar 70 through discrete torque setting positions.

[0018] 2-6, the clutch mechanism 66 further includes a thrust washer assembly 98 that allows movement (if any) between the clutch spring 78 and the gear case 38. Specifically, the thrust washer assembly 98 includes a first washer 102 (FIG. 4) that is rotationally constrained to the gear case 38, and a second washer 104 that is in sliding contact between the first washer 102 and the spring end plate 86. The second washer 104 includes a plurality of pockets 106 that receive corresponding spherical rollers 110 for rolling along a flat surface 114 of the first washer 102. The clutch spring 78 is compressed between the nut 74 and the thrust washer assembly 98, which places tension on the neck portion 91 of the gear case 38. While the thrust washer assembly 98 is incorporated in this embodiment, the thrust washer assembly 98 may be omitted in other embodiments.

[0019] Once the user has selected the desired torque setting, the clutch adjustment assembly 68 prevents any intentional or inadvertent adjustments by a lockout mechanism 124 (FIG. 5). The lockout mechanism 124 mechanically interferes with the collar 70 to prevent rotational movement thereof. The lockout mechanism 124 may be coupled to, for example, the gear case 38 and selectively interferes with the collar 70 such that the collar 70 cannot rotate relative to the gear case 38. The lockout mechanism 124 may be manually or automatically actuated. That is, a user may manually actuate the lockout mechanism 124 between a locked state, in which the collar 70 is prevented from rotational movement, and a released state, in which the collar 70 may be allowed to rotate. Alternatively, the power tool 10 may automatically actuate the lockout mechanism 124 between the locked and released states. In other embodiments, if the tool 10 does not operate when the user pulls the trigger switch 40, the lockout mechanism 124 may simply provide a visual or audio indication to the user if the torque setting on the tool 10 is different than the specified torque setting in the mobile application (e.g., the OneKey® app). In this case, the power tool 10 or mobile application may have a confirmation button (physical or touch screen) that must be actuated to confirm that the user intended to adjust the clutch adjustment assembly 68. In yet other embodiments, the lockout mechanism 124 may alternatively be an electromechanical lockout where an electronic switch or mobile application can actuate the lockout mechanism 124 between a locked and released state.

[0020] 5-8, the clutch mechanism 66 further includes a washer 134 circumferentially disposed about the neck portion 91 of the gear case 38 and surrounded by the collar 70. The washer 134 interfaces with a series of pins 138 and balls 142 (FIGS. 5 and 6) disposed within corresponding openings 144 in the gear case 38 (FIG. 9). The series of pins 138 and the series of balls 142 are axially aligned within the openings 144. A compressive force from the clutch spring 78 is imparted to the washer 134 via the thrust washer assembly 98. The washer 134 then transfers the compressive force of the clutch spring 78 to the series of pins 138 and the series of balls 142 during a clutch event, as will be described in more detail below. Outside of a clutch event, the washer 134 simply presses against a front face 146 of the gear case 38 (FIGS. 6 and 8).

[0021] 5-8, the washer 134 includes an L-shaped tab or arm 136 extending from an outer periphery of the washer 134. The arm 136 is received within a slot 148 in a front face 146 of the gear case 38. The arm 136 may contact a switch 149 (FIG. 7) when the washer 134 is displaced from the front face 146 of the gear case 38 during a clutch event, as will be described in more detail below.

[0022] 5-8, the clutch mechanism 66 further includes a ring gear 150 having a series of projections 154 extending axially from the ring gear 150 toward the series of balls 142. The ring gear 150 of the third stage gear set 54 includes teeth 158 (FIG. 5) that mesh with the output carrier 56 and the planetary gears 58 that drive the output shaft 22. The ring gear 150 is rotatable relative to the gear case 38. In normal operation, the series of balls 142 engage a flat rim 162 of the ring gear 150 and pack against the projections 154, locking the ring gear 150 against rotation so that torque can be transferred from the motor 18 to the output shaft 22. However, during a clutch event, the ring gear 150 rotates (or slips) relative to the gear case 38 causing the projection 154 to slide past the set of balls 142, thereby imparting axial displacement to the set of pins 138 and washers 134 against the bias of the clutch spring 78. This occurs when the reaction torque on the workpiece exceeds the compression force of the clutch spring 78. The projection 154 continues to slide past the set of balls 142 for as long as the reaction torque of the output shaft 22 exceeds the compression force of the clutch spring 78. If the operator of the power tool 10 decides to adjust the tool 10 to a higher or lower torque setting, the operator need only adjust the collar 70 to increase or decrease the compression force (i.e., preload) applied by the clutch spring 78.

[0023] 8, the power tool 10 includes a main clutch sensor 166 disposed within a cavity 170 of the gear case 38. Specifically, the main clutch sensor 166 is disposed at the base of the neck portion 91, an area that is resistant to bending but susceptible to strain when under tension. The sensor 166 may be configured as one or more strain gauges. For example, if multiple strain gauges are used, the multiple strain gauges may be configured in a Wheatstone bridge. The sensor 166 detects the strain applied to the neck portion 91 of the gear case 38, which is proportional to the preload of the clutch spring 78. Thus, as the preload of the clutch spring 78 (via the nut 74 and its threaded connection to the neck portion 91) increases, the amount of strain applied to the neck portion 91 increases. This relationship may be used to determine the torque setting without relying on predefined discrete torque settings for the collar 70, which may become inaccurate over time of the tool due to wear on the clutch mechanism 66. In some embodiments, there may be multiple sensors 166 to provide robustness to detection of other deformations caused by, for example, bending stresses, shear stresses, and temperature expansion / contraction stresses.

[0024] 8 and 9, the power tool 10 includes a user interface 178 for providing real-time feedback indicative of the torque setting at which the power tool 10 is set. The torque settings displayed to the user via the user interface 178 are based on mapping the strain signals generated by the sensor 166 when the clutch spring 78 is set at various preloads between (and including) low and high torque settings. As shown in FIG. 9, the main clutch sensor 166 detects the amount of strain applied to the neck portion 91 when the clutch mechanism 66 is at various torque settings and outputs corresponding signals (e.g., levels A, B, C, D). That is, each level A, B, C, D represents a discrete position of the clutch mechanism 66 that generates a different strain signal at the main clutch sensor 166. While the strain signals generated in the illustrated embodiment are discrete, in other embodiments the force signal generated may be continuous where the clutch mechanism 66 provides the user with infinite levels of torque settings between the high and low torque settings. The user interface 178 may be provided on an external device such as a smartphone. In addition to, or instead of, the user interface 178, the power tool 10 may include one or more user feedback LEDs (light emitting diodes) or LCDs (liquid crystal displays) 179 (FIG. 1) located on the top of the tool 10 or elsewhere viewable by a user while the tool 10 is in operation.

[0025] Referring to FIG. 5, the power tool 10 may also include a current sensor 182 that monitors the current drawn by the motor 18, which is also proportional to the torque output of the motor 18. A motor control unit, or MCU 186, located in the handle 34 (FIG. 2), receives and compares the motor current signal from the current sensor 182 and the strain signal from the main clutch sensor 166 to determine the accuracy of the strain signal. The accuracy of the strain signal may change over the life of the tool due to, for example, normal wear of the clutch spring 78 or any other component of the clutch mechanism 66. Thus, the motor current signal provides a first reference signal (or a first default signal) for the MCU 186 to compare with the force signal. In response to a large variance or deviation between the first reference signal (e.g., the motor current signal) and the strain signal, the user interface 178 may prompt the user to adjust the clutch mechanism 66 or recalibrate the power tool 10 to eliminate an overshoot or undershoot in the torque delivered by the tool 10.

[0026] For example, as described in more detail below, the first reference signal may be higher or lower than the strain signal from the main clutch sensor 166, at which point the user may adjust the clutch mechanism 66 or recalibrate the tool. In addition to or instead of the motor current sensor 182, a load cell or transducer 190 (FIG. 5) may be provided on or adjacent to the ring gear 150 to provide a second reference signal (or a second default signal) to the MCU 186. The transducer 190 may be similar to the disclosed transducer assembly identified as 54 in FIG. 4 of U.S. Pat. No. 10,357,871, the entire contents of which are incorporated herein by reference. The second reference signal is in the form of a strain signal indicative of the amount of rotational strain imparted to the ring gear 150, which is proportional to the reaction torque imparted to the tool bit. The first and second reference signals provide real-time feedback of the components undergoing strain. Thus, the MCU 186 may compare the first reference signal to the second reference signal to determine the accuracy of the strain signal generated by the main clutch sensor 166 .

[0027] In the case where the user interface 178 prompts the user to recalibrate the power tool 10, the user may input a calibration setting for the tool 10. In the calibration setting, the user may first calibrate the tool 10 by mechanically adjusting the torque setting of the tool 10 via the clutch adjustment assembly 68. The tool 10 then provides its own estimate of the approximate torque at which the clutch mechanism 66 will undergo a clutch event. The user then operates the tool 10 while being monitored by a test device (not shown) that checks the performance of the tool 10. The test device provides an adjustment factor that accounts for the difference between the original estimate and the actual performance. At this point, the adjustment factor is stored in the MCU 186, so that the original estimate provided by the user interface 178 is accurate to the actual performance.

[0028] In other embodiments, the manufacturer may alternatively calibrate the power tool 10. For example, the manufacturer measures the maximum torque output by the power tool 10 at a high torque setting. When the power tool 10 is at the high torque setting and undergoes a clutch event, the maximum torque output is determined. Similarly, the manufacturer measures the minimum torque output by the power tool 10 at a low torque setting. When the power tool 10 is at the low torque setting and undergoes a clutch event, the minimum torque output is determined. The torque output at each discrete torque setting between the high and low torque settings is also determined, at which point the mapping is stored in the tool 10.

[0029] In yet another embodiment, the power tool 10 need only be calibrated by comparing the force signal generated by the main clutch sensor 166 to the first and second reference signals. Specifically, once the tool 10 is in the calibration setting, the tool 10 is operated to drive a workpiece, at which point the MCU 186 records the signals from the motor current sensor 182 and the transducer 190. Upon detecting a significant difference or deviation between the first reference signal (e.g., the motor current signal) and the force signal, or between the second reference signal (e.g., the strain signal) and the force signal, the MCU 186 records an adjustment factor so that the user interface 178 can display the correct torque setting.

[0030] To operate a torque tool at a low torque setting (FIG. 2), a user engages the output shaft 22 with an object, such as a fastener. When the motor 18 begins to rotate, the third stage gear set 54 transmits torque to the output carrier 56 through the clutch mechanism 66. The output shaft 22, which is coupled to the output carrier 56, rotates and thus exerts a torque on the fastener. When a low torque is reached, the torque imparted through the output shaft 22 overcomes the compressive force of the clutch mechanism 66. This causes the ring gear 150 to slide or slip over the set of balls 142.

[0031] Specifically, as ring gear 150 rotates relative to gear case 38, protrusion 154 slides past set of balls 142, at which point the apex of protrusion 154 axially displaces set of balls 142 and set of pins 138 through opening 144. This displacement also displaces washer 134 such that arm 136 contacts (e.g., directly, electrically, etc.) switch 149. Switch 149 then relays a signal to MCU 186 that a clutch event has occurred.

[0032] When the power tool 10 undergoes this clutch event, the torque that the output shaft 22 was providing to the workpiece is interrupted. That is, the power tool 10 is stopped upon detection of a single clutch event. When a clutch event occurs in the clutch mechanism 66, the motor current signal detected by the motor current sensor 182 changes suddenly. The sudden change in the motor current signal is relayed from the motor current sensor 182 to the MCU 186, at which point the power tool 10 is stopped via the MCU 186. Thus, when the power tool 10 is at a low torque setting, the output shaft 22 can accurately apply a low torque to the fastener, and cannot apply a torque beyond the low torque setting to the fastener due to the power tool 10 being stopped upon detection of a clutch event. In some embodiments, the signal sent by the switch 149 to the MCU 186 can additionally or alternatively stop the power tool 10.

[0033] 3, the clutch mechanism 66 is actuated to the high torque setting by rotating the collar 70, which translates the nut 74 and compresses the clutch spring 78. In the illustrated embodiment, the collar 70 is rotated until the nut 74 translates to the high torque setting. The collar 70 stops rotating when the nut 74 reaches the high torque setting, indicating that the clutch mechanism 66 is set to the high torque setting. The nut 74 compresses the clutch spring 78, which exerts a greater compressive force against the thrust washer assembly 98 and washer 134.

[0034] To operate the power tool 10 in the high torque setting (FIG. 3), a user engages the output shaft 22 with an object, such as a fastener. When the motor 18 begins to rotate, the third stage gear set 54 transmits torque to the output carrier 56 through the clutch mechanism 66. The output shaft 22, which is coupled to the output carrier 56, rotates and thus exerts a torque on the fastener. When high torque is reached, the torque imparted through the output shaft 22 overcomes the compressive force of the clutch mechanism 66. This causes the ring gear 150 to slide or slip over the set of balls 142.

[0035] Specifically, as ring gear 150 rotates relative to gear case 38, protrusion 154 slides past set of balls 142, at which point the apex of protrusion 154 axially displaces set of balls 142 and set of pins 138 through opening 144. This displacement also displaces washer 134 such that arm 136 contacts switch 149. Switch 149 then relays a signal to MCU 186 that a clutch event has occurred.

[0036] When the power tool 10 undergoes this clutch event, the torque that the output shaft 22 was providing to the workpiece is interrupted. That is, the power tool 10 is stopped upon detection of a single clutch event. When a clutch event occurs in the clutch mechanism 66, the motor current signal detected by the motor current sensor 182 changes suddenly. The sudden change in the motor current signal is relayed from the motor current sensor 182 to the MCU 186, at which point the power tool 10 is stopped via the MCU 186. Thus, when the power tool 10 is at the high torque setting, the output shaft 22 can accurately apply high torque to the fastener, but cannot apply torque beyond the high torque setting to the fastener due to the power tool 10 being stopped upon detection of the clutch event. In some embodiments, the signal sent by the switch 149 to the MCU 186 can additionally or alternatively stop the power tool 10.

[0037] To return the power tool 10 to the low torque setting, the user rotates the collar 70 until the nut 74 translates to the low torque setting (FIG. 2). In the low torque setting, the nut 74 is positioned to allow the clutch spring 78 to expand to a length nominally greater than its compressed length in the high torque setting.

[0038] In a further embodiment, the power tool 10 operates at variable torque settings by rotating the collar 70 to translate the nut 74 to specific positions between a low torque setting (FIG. 2) and a high torque setting (FIG. 3). The clutch spring 78 is compressed by different amounts at each of the discrete positions, which creates corresponding compressive forces on the thrust washer assembly 98 and washer 134. This causes the clutch mechanism 66 to produce different and precise torque outputs at each of the torque settings.

[0039] In further embodiments, the power tool 10 operates at variable torque settings by electronically varying the compression of the clutch spring 78 using an electroactive polymer material, a linear actuator, or a hydraulic actuator. The electroactive polymer material may, for example, surround the clutch spring 78 and change size (e.g., deform) when stimulated by an electric field, thereby varying the compression of the clutch spring 78 in response to deformation of the electroactive polymer material. In such embodiments, the clutch spring 78 and collar 70 may be omitted and adjustment of the clutch mechanism 66 may be made electronically (e.g., using the user interface 178).

[0040] In yet another embodiment, the power tool 10 operates at variable torque settings by using the motor 18 to vary the compression of the clutch spring 78. Typically, the motor 18 drives only the output shaft 22, but in such an alternative embodiment, a user may bias the application of torque by the motor 18 from the output shaft 22 to the clutch spring 78. That is, a shifting mechanism may be provided that selectively couples the motor 18 to the clutch spring 78 such that the motor 18 is actuated to vary the compression of the clutch spring 78. Instead of adjusting the collar 70, the user simply actuates the shifting mechanism to a clutch adjustment mode and then depresses the trigger switch 40 to actuate the motor 18 to compress / decompress the clutch spring 78.

[0041] While the switch 149 may send a signal to the MCU 186 to shut down the power tool 10 in response to a clutch event, in other embodiments, similar types of sensors may alternatively be positioned adjacent to and detect axial displacement of the clutch spring 78, the spring end plate 86, the thrust washer assembly 98, the set of pins 138, and / or the set of balls 142. Axial displacement of any component in the clutch mechanism 66 is indicative of the set of balls 142 being displaced by the protrusion 154 of the ring gear 150 during a clutch event.

[0042] The MCU 186 may also be configured to shut down the power tool 10 when the detected torque is a certain percentage greater than the target torque set by the clutch mechanism 66. For example, if a user sets the target torque via the clutch mechanism 66 to 100 ft-lbs and limits the overshoot probability to 10%, the power tool 10 may automatically shut down the power tool 10 when it experiences a reaction torque of 110 ft-lbs. In some embodiments, the user can set an upper limit on the overshoot probability to 5%, 10%, or any value within the clutch capability where the output fluctuation includes the clutch fluctuation.

[0043] Figures 10-13 show a main clutch sensor 466 according to another embodiment of the present invention. The main clutch sensor 466 shown in Figures 10-13 is similar to the main clutch sensor 166 of the power tool 10 shown in Figures 1-9, and like structure is identified with like reference numbers plus 300. The main clutch sensor 466 can detect the compressed length of the spring 378 to determine a preload on the clutch spring 378, which is then transmitted to the user in the form of a torque setting for the clutch mechanism 366.

[0044] 10, the main clutch sensor 466 includes an inductive sensor 474 and a conductor or target 376. In this embodiment, the conductor 376 is a clutch spring 378, which is positioned adjacent to and offset from the inductive sensor 474. In another embodiment, as shown in FIG. 14, the main clutch sensor 766 includes a conductor or target 676 (e.g., spring 678) that is positioned circumferentially around the inductive sensor 774 instead of being positioned parallel to the inductive sensor 774.

[0045] 10, the inductive sensor 474 includes a first end 494 and a second end 498 opposite the first end 494. The inductive sensor 474 can transmit an inductive signal to the MCU 486. The inductive sensor 474 is configured to have a coiled wire. When an AC voltage is applied to the sensor 474, an electromagnetic field is generated. Based on Faraday's law of electromagnetic induction, a voltage is induced in the conductor 376 in response to the relative motion between the conductor 376 and the magnetic field of the inductive sensor 474, which generates an eddy current in the conductor 376 that opposes the electromagnetic field generated by the inductive sensor 474. This causes a change in the inductance of the inductive sensor 474, which can be measured to determine the compressed length L of the spring 378 (i.e., L 0 , L 1 , L 2 10, inductive sensor 474 is configured as an LC tank circuit whose frequency (hereafter referred to as the "inductive signal") changes in response to changes in inductance.

[0046] As shown in FIG. 10, the inductive sensor 474 is a linear inductive sensor having a non-uniform winding density along the length of the inductive sensor 474. In other words, the inductive sensor 474 has a relatively low winding density at a first end 494 of the sensor 474 and a relatively high winding density at a second end 498 of the sensor 474. The change in measured inductance of the sensor 474 in response to movement of the conductor 376 (e.g., clutch spring 378) relative to the inductive sensor 474 may be used to indicate to a user what torque setting the power tool 10 is set to. In other embodiments, as shown in FIG. 15, the main clutch sensor 1066 includes an inductive sensor 1074 that may alternatively have a uniform winding density such that the number or density of windings is the same throughout the length (or diameter) of the sensor.

[0047] 10 to 13, the signal output by the inductive sensor 474 changes when the clutch spring 378 is compressed. For example, when the compressed length L of the clutch spring 378 (or the conductor 376) is L 0 In FIG. 10, the induction sensor 474 is 0 The coil density of the clutch spring 378 is then relayed to the MCU 486. Similarly, when the compressed length L of the clutch spring 378 (or the conductor 376) is 1 (FIG. 11), the induction sensor 474 is L 1 The induction signal corresponding to the coil density of the clutch spring 378 is relayed to the MCU 486. 2 An induction signal corresponding to the coil density for (FIG. 12) or any other length is also sent to the MCU 486. The MCU 486 is pre-programmed to output to the user interface 178 the torque setting for the power tool 10 corresponding to the induction signal generated at each compression length L.

[0048] In operation of the power tool 10 using the embodiment of the main clutch sensor 466, 766, 1066 shown in FIGS. 10-15, a user adjusts a torque setting via the clutch mechanism 366, 666, 966 to compress the conductor 376, 676, 976 (e.g., spring 378, 678, 978). As the compressed length L decreases, the coil density of the conductor 376, 676, 976 increases, which in turn proportionally changes the output (e.g., inductive signal) of the inductive sensor 474, 774, 1074. The inductive signal is relayed to the MCU 486, which processes the signal to determine which compressed length L is associated with the signal. Once the MCU 486 determines the compressed length L via the received inductive signal, a preload (or particular torque setting) is interpolated and displayed to the user via the user interface 178. For example, the inductive sensor 474, 774, 1074 may adjust the torque setting to determine whether the conductor 376, 676, 976 is at or near the length L. 0 10, the first guidance signal is relayed to the MCU 486, which in turn transmits the first guidance signal with a length L 0 , i.e., the clutch mechanism 366, 666, 966 is at a low torque setting. The user interface 178 then notifies the user that the power tool 10 is at the low torque setting. When the operator adjusts the torque setting via the clutch mechanism 366, 666, 966 to a high torque setting (or any incremental torque setting between the low and high torque settings), the conductor 376, 676, 976 (e.g., spring 378, 678, 978) is further compressed. This compression causes a change in the inductive signal generated by the inductive sensor 474, 774, 1074. A second inductive sensor detects whether the conductor 376, 676, 976 has a length L 2 (FIG. 12), the second guidance signal is relayed to the MCU 486, at which point the MCU 486 transmits a second guidance signal of length L 2 That is, the clutch mechanism 366, 666, 966 is at a high torque setting.

[0049] In the calibration setting, a user may first calibrate the tool 10 by mechanically adjusting the torque setting of the tool 10 via the clutch adjustment assembly 68 to, for example, a high torque setting. When the power tool 10 is at the high torque setting and goes through a clutch event, a maximum torque output is determined. The user then mechanically adjusts the torque setting of the tool 10 via the clutch adjustment assembly 68 to a low torque setting. When the power tool 10 is at the low torque setting and goes through a clutch event, a minimum torque output is determined. The tool 10 now has two points stored (e.g., a low point and a high point), at which point linear interpolation may be used to self-calibrate the tool 10 using inductive based measurements via the inductive sensors 474, 774, 1074.

[0050] Figure 16 illustrates a main clutch sensor 1366 according to another embodiment of the present invention. The main clutch sensor 1366 illustrated in Figure 16 is similar to the main clutch sensor 466 of the power tool 10 illustrated in Figures 10-13, and like structure is identified by like reference numerals plus "900."

[0051] 16, the main clutch sensor 1366 includes an inductive sensor 1374 and a conductor or target 1276. In this embodiment, the conductor 1276 is coupled to the clutch spring 1278 and cantilevers away from the clutch spring 1278, overlapping the inductive sensor 1374. That is, the clutch spring 1278 is adjacent to and offset from the main clutch sensor 1366, and the conductor 1276 is aligned with and overlaps the main clutch sensor 1366. The inductive sensor 1374 includes a first end 1394 and a second end 1398 opposite the first end 1394. The conductor 1276 is relatively narrow relative to the inductive sensor 1374, allowing accurate detection of where exactly the conductor 1276 is located relative to the inductive sensor 1374. Specifically, the inductive sensor 1374 can detect whether the conductor 1276 is located adjacent the first end 1394, adjacent the second end 1398, or somewhere between the first end 1394 and the second end 1398. In some embodiments, the conductor 1276 is a nut 74, such that movement of the nut 74 causes a change in inductance of the sensor 474, and the change in inductance can be measured to indicate to a user whether the power tool 10 is set to its torque setting.

[0052] As shown in FIG. 16, the inductive sensor 1374 is a linear inductive sensor having a non-uniform winding density along the length of the inductive sensor 1374. In other words, the inductive sensor 1374 has a relatively low winding density at a first end 1394 of the sensor 1374 and a relatively high winding density at a second end 1398 of the sensor 1374. In other embodiments, as shown in FIG. 17, the main clutch sensor 1666 includes an inductive sensor 1674 that may alternatively have a uniform winding density such that the number or density of windings is the same throughout the length (or diameter) of the sensor. And in other embodiments, as shown in FIG. 18, the main clutch sensor 1766 includes an inductive sensor 1774 that may alternatively have sine and cosine geometries. In this embodiment of the main clutch sensor 1366, the change in measured inductance of the sensor 1374 in response to movement of the conductor 1276 relative to the sensor 1374 can be used to indicate to a user which torque setting the power tool 10 is set to.

[0053] Figure 19 illustrates a main clutch sensor 1966 according to another embodiment of the present invention. The main clutch sensor 1966 illustrated in Figure 19 is similar to the main clutch sensor 466 of the power tool 10 illustrated in Figures 10-13, and like structure is identified by like reference numerals plus the addition of "1500."

[0054] 19, the main clutch sensor 1966 includes a first inductive sensor 1974a, a second inductive sensor 1974b, and a conductor or target 1876. In this embodiment, the conductor 1876 is a clutch spring 1878, and the conductor 1876 is circumferentially disposed around the inductive sensors 1974a, 1974b. In other embodiments, the conductor 1876 (e.g., the spring 1878 or a cantilever arm) may alternatively be adjacent to and offset from the first and second inductive sensors 1974a, 1974b. As shown in FIG. 19, the inductive sensors 1974a, 1974b are circular inductive sensors with uniform winding density along the diameter of the inductive sensors 1974a, 1974b. In other embodiments, the inductive sensors 1974a, 1974b may alternatively have a non-uniform winding density such that the number of windings or winding density varies throughout the length of the sensor. In this embodiment of the main clutch sensor 1966, the change in measured inductance of the sensors 1974a, 1974b in response to movement of the conductor 1876 relative to the sensors 1974a, 1974b can be compared to a constant reference signal from the reference clock 1972 to indicate to a user what torque setting the power tool 10 is set to.

[0055] The first inductive sensor 1974a is disposed adjacent a first end 1888 of the clutch spring 1878, and the second inductive sensor 1974b is disposed adjacent a second end 1890 of the clutch spring 1878. The first inductive sensor 1974a and the second inductive sensor 1974b are stationary such that the inductive sensors 1974a, 1974b do not move when the torque mechanism 1866 is adjusted between low and high torque settings. The inductive sensors 1974a, 1974b may transmit an inductive signal to the MCU 1986 corresponding to the relative motion between the conductor 1876 and the magnetic fields of the inductive sensors 1974a, 1974b. As described above, this generates eddy currents in the conductor 1876 that oppose the electromagnetic fields created by the inductive sensors 1974a, 1974b. This causes a change in inductance of the inductive sensors 1974a, 1974b, and the change in inductance is proportional to the length L of the conductor 1876 (e.g., L 0 , L 1 , L 2 ), and thus is used in part to determine the amount of torque.

[0056] 19, the reference clock 1972 is isolated from the conductor 1876 so that the reference clock 1972 is not affected by eddy currents in the conductor 1876. The reference clock 1972 is therefore operable to output a constant reference signal, the purpose of which will be described in more detail below. The MCU 1986 and the main clutch sensor 1366 receive the outputs of the inductive sensors 1974a, 1974b and the reference clock 1972, and are electrically connected to the user interface 178. The MCU 1986 continuously receives a first inductive signal indicative of a change in position of the conductor 1876 from the first inductive sensor 1974a, a second inductive signal indicative of a change in position of the conductor 1876 from the second inductive sensor 1974b, and the constant reference signal from the reference clock 1972.

[0057] Using the first and second induction signals and a constant reference signal as inputs, the MCU 1986 is operable to calculate a frequency ratio, which is the ratio of the induction signal to the constant reference signal. Specifically, the MCU 1986 calculates a first frequency ratio and a second frequency ratio and digitally outputs to the MCU 1986 a first ratio signal indicative of the first frequency ratio and a second ratio signal indicative of the second frequency ratio. The MCU 1986 is operable to interpolate the first ratio signal and the second ratio signal to determine what torque setting the tool 10 is set to. Once the torque setting is determined, the MCU 1986 outputs the torque setting to the user interface 178.

[0058] Various features of the invention are set forth in the following claims.

Claims

1. Gear case and an output shaft extending from the gear case; a drive mechanism configured to provide a torque to the output shaft to rotate the output shaft; a clutch mechanism between the output shaft and the drive mechanism, the clutch mechanism being configured to limit an amount of torque provided by the output shaft, the clutch mechanism including a compression spring; a clutch adjustment assembly configured to adjust a compression length of the compression spring; a lockout mechanism that is adjustable between a locked state in which the clutch adjustment assembly is prevented from adjusting the compressed length of the compression spring and a released state in which the clutch adjustment assembly is allowed to adjust the compressed length of the compression spring. Rotary power tools.

2. 2. The rotary power tool of claim 1, wherein the clutch adjustment assembly includes a collar circumferentially disposed about a neck portion of the gear case and a nut threadedly engaged with the neck portion of the gear case, the nut co-rotating with the collar to adjust the compressed length of the compression spring.

3. The rotary power tool of claim 2 , wherein the lockout mechanism mechanically interferes with the collar such that the collar cannot rotate relative to the gear case.

4. 2. The rotary power tool of claim 1, further comprising an electronic control unit configured to receive an output signal from a sensor indicative of the compressed length of the compression spring, the electronic control unit configured to determine a torque setting for the clutch mechanism based on the output signal.

5. The rotary power tool of claim 4 , wherein the lockout mechanism sends another output signal to the electronic control unit to alert a user when the torque setting of the clutch mechanism is adjusted by the clutch adjustment assembly.

6. Gear case and an output shaft extending from the gear case; a drive mechanism configured to provide a torque to the output shaft to rotate the output shaft; a clutch mechanism between the output shaft and the drive mechanism, the clutch mechanism being configured to limit an amount of torque provided by the output shaft and including a compression spring positioned about the output shaft; a clutch adjustment assembly having a collar circumferentially disposed about the gear case and rotatable to adjust a length of the compression spring; the inductive sensor disposed within the collar proximate to the compression spring such that a voltage is induced in the inductive sensor in response to relative motion between the compression spring and a magnetic field emitted by the inductive sensor; an electronic control unit configured to receive an output signal from the inductive sensor indicative of a change in inductance in the inductive sensor and to determine a parameter of the clutch mechanism based on the output signal; the compression spring is disposed adjacent to and offset from the inductive sensor; Rotary power tools.

7. The rotary power tool of claim 6 , wherein the electronic control unit is configured to correlate the output signal of the inductive sensor with a length of the compression spring.

8. 7. The rotary power tool of claim 6, wherein the clutch mechanism is adjustable via the clutch adjustment assembly between a first torque setting, a second torque setting, and a plurality of discrete torque settings between the first torque setting and the second torque setting.

9. 7. The rotary power tool of claim 6, wherein the collar is circumferentially disposed around a neck portion of the gear case, and a nut is threadedly engaged with the neck portion of the gear case, the nut co-rotating with the collar to adjust a length of the compression spring.

10. 7. The rotary power tool of claim 6, further comprising a motor operably coupled to the drive mechanism and a motor sensor that detects an amount of current drawn by the motor, the electronic control unit configured to identify a clutch event based on feedback from the motor sensor, and the electronic control unit configured to stop the motor when the clutch event occurs.

11. 7. The rotary power tool of claim 6, further comprising a switch interfaced with the clutch mechanism, the electronic control unit configured to identify a clutch event based on feedback from the switch, and the electronic control unit configured to stop the motor when the clutch event occurs.

12. The rotary power tool of claim 6, further comprising a user interface, wherein the electronic control unit sends a signal to cause the user interface to display discrete torque settings based on the determined torque setting of the clutch mechanism.

13. Gear case and an output shaft extending from the gear case; a drive mechanism that provides torque to the output shaft to rotate the output shaft; a clutch mechanism configured to limit an amount of torque provided by the output shaft, the clutch mechanism including a first plate, a second plate, and a compression spring disposed between the first plate and the second plate, the first plate moving in response to a clutch event to momentarily change a length of the compression spring; a clutch adjustment assembly configured to change the length of the compression spring by moving the second plate relative to the compression spring; an inductive sensor adjacent to the compression spring such that a voltage is induced in the inductive sensor in response to a change in the length of the compression spring relative to a magnetic field emitted by the inductive sensor; the compression spring is circumferentially disposed about the inductive sensor; Rotary power tools.

14. The rotary power tool of claim 13, further comprising an electronic control unit configured to receive an output signal from the inductive sensor indicative of a change in inductance in the inductive sensor, and to determine a parameter of the clutch mechanism based on the output signal.

15. The rotary power tool of claim 14, further comprising a user interface, wherein the electronic control unit sends a signal to cause the user interface to display discrete torque settings based on the determined torque setting of the clutch mechanism.

16. 14. The rotary power tool of claim 13, wherein the clutch mechanism is adjustable via the clutch adjustment assembly between a first torque setting, a second torque setting, and at least one discrete torque setting between the first and second torque settings.

17. 14. The rotary power tool of claim 13, wherein the clutch adjustment assembly includes a collar circumferentially disposed about a neck portion of the gear case, a nut threadedly engaged with the neck portion of the gear case, the nut co-rotating with the collar to move the second plate and adjust the length of the compression spring.

18. 14. The rotary power tool of claim 13, wherein the clutch mechanism further includes a series of balls that interface with and slide over a series of protrusions during a clutch event, displacing the series of balls axially toward the first plate and causing the series of balls to move the first plate against the bias of the compression spring.

19. The rotary power tool of claim 13 further comprising a switch that is actuated when the first plate moves, such that the motor is stopped when the clutch event occurs.

20. The rotary power tool of claim 13 , wherein the output shaft extends beyond the gear case.

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