Power tool and two-speed gear assembly for a power tool

Abstract

This specification relates to a power tool including an input shaft, an output shaft, and a two-speed power transmission (T), the two-speed power transmission including planetary gears (4) and a gear shift assembly for directing torque through or past the planetary gears, the gear shift assembly including a drive member (2), a driven member (1), and an axially movable coupling sleeve (6) arranged to interconnect the drive member (2) and the driven member (1) in a first position and to interconnect the planetary gears (4) and the drive member (1) in a second position. A linear actuator (13, 14) includes a linearly movable push bar (13) arranged to displace the coupling sleeve between the first and second positions. This specification also relates to a method in and to a two-speed power transmission for such a power tool.

Description

[Technical field]

[0001] The present invention relates generally to power tools, and more particularly to power tools having a two speed gear assembly. [Background technology]

[0002] Various types of power tools are known to be used in various industrial sectors, a common one being a fastening tool used for fastening screws or bolts.

[0003] One issue that is known to cause various design challenges in the field is that the working conditions and the demands on expected power output tend to vary greatly during use, for example with regard to the speed and torque required in different parts of a typical work process. This is for example the case of the above mentioned fastening tools where in the initial stage of fastening a screw or a nut, i.e. the so-called run-down, the torque required is low but the rotational speed should ideally be high to reduce the time required for the operation, whereas in the actual fastening stage, i.e. the actual tightening of the joint, the torque required is high.

[0004] However, power tools subject to these types of varying requirements are known to include one or more power transmissions, such as one or more planetary gear stages connected in series, to provide the desired torque levels.

[0005] However, the use of such power transmissions to achieve the high torque levels required for actual tightening leads to undesirably low rotational speeds during rundown, as the rotational speed provided is correspondingly reduced. This is particularly a significant problem in the field of power tools adapted to tighten large screws at very high torque values, where providing the desired high torque typically results in very low rotational speeds, which usually results in an unreasonably slow rundown phase.

[0006] Therefore, to alleviate some of these problems, attempts have been made to use two-speed power transmissions, i.e., power transmissions which can modify the flow of force through the gear unit to use the higher rotational speed during rundown and only use the high torque / low speed mode when necessary during actual engagement.

[0007] However, there remain many problems associated with such power transmissions. For example, one known problem is the lack of control over the actual progress of the shifting operation, i.e., not knowing whether the shifting has actually been performed correctly or not. This lack of precise control over the actual current positions of the gear elements can lead to the destruction of gears and couplings.

[0008] Solutions proposed involve complex mechanisms including synchronizing rings or bulky sensors, which are therefore complex to design and generally require a large amount of space.Therefore, there is a need for improvements in the field of two-speed gear units for power tools. Summary of the Invention [Means for solving the problem]

[0009] It would therefore be desirable to provide a power tool with an improved two-speed transmission. In particular, it would be desirable to provide a transmission that offers improved possibilities for controlling the speed changes. In order to better solve one or more of these problems, a gear unit for a fastening tool, a power tool comprising such a gear unit and a method for controlling such a power tool are provided, as defined in the independent claims. Preferred embodiments are defined in the dependent claims.

[0010] According to a first aspect of the present invention there is provided a power tool with a two speed power transmission comprising a housing, an input shaft, an output shaft and a two speed power transmission comprising planetary gears and a two speed gear shift assembly for directing torque through the planetary gears in a high torque / low drive speed mode or past the planetary gears in a low torque / high drive speed mode. The gear shift assembly comprises a drive member drivingly connected to the input shaft, a driven member drivingly connected to the output shaft, an axially movable coupling sleeve arranged to interconnect the drive member and the driven member at a first position and to interconnect the planetary gears and the driven member at a second position, and a linear actuator arranged to displace the axially movable coupling sleeve between the first and second positions, the linear actuator comprising a linearly movable push bar arranged to displace the coupling sleeve between the first and second positions.

[0011] According to a first aspect, a two-speed transmission provides an inventive solution to the above mentioned problems by its design incorporating a gear shifting mechanism which directs torque through a planetary gear stage in high torque / low speed drive mode or past the planetary gears in low torque / high speed drive mode, with improved possibilities for precisely controlling the speed change being provided by the use of a coupling sleeve displaced by a linear actuator.

[0012] In particular, a linear actuator is positioned to displace the coupling sleeve so that engagement (or lack thereof) in each mode of operation can be determined based on the position of the linear actuator. Thus, this design cleverly provides a two-speed power transmission that can provide precise and accurate control of gear shifting.

[0013] According to one embodiment, the power tool further comprises a motor and means for monitoring the torque delivered by the tool. The means for monitoring the torque delivered by the tool may comprise a sensor, such as a torque transducer, for example. Other examples include circuitry adapted to monitor the motor current or other internally provided data relating to the performance of the motor. The power tool may also form part of a system including the power tool and an external controller operative to control the power tool.

[0014] Regarding such power tools, according to one embodiment, the motor is an electric motor. The tool can be, for example, a hand-held power tool selected from the group consisting of a screwdriver, a nut runner, a drill and a grinder. However, a person skilled in the art will understand that only minor modifications of the structure will be necessary for use with fixed tools or fixed tools. In some embodiments, the power tool can be a battery-powered power tool. In one embodiment, the power tool is a tool that provides a higher fastening torque, for example in the range of 2400 to 8000 Nm.

[0015] According to one embodiment, the gear shift assembly further comprises a coupling assembly arranged between the coupling sleeve and the linear actuator, the coupling assembly comprising a first element rotatably coupled to the sleeve and a second element translatably coupled to the push bar, the rotation of the first element being independent of the rotation of the second element, the second element being arranged to push the first element axially, such that rotation of the sleeve, and therefore the motor, does not affect the linear actuator, and adjustment of the axial position of the sleeve can be made independent of the rotation. The second element can form part of the push bar.

[0016] In one embodiment, the gear shift assembly further comprises a coupling assembly arranged to couple (i.e. link or connect) the coupling sleeve and the linear actuator, the coupling assembly comprising a first element rotatably coupled to the sleeve and a second element translatably coupled to the push bar, wherein rotation of the first element is independent of rotation of the second element, the second element being arranged to push the first element axially, such that rotation of the sleeve, and therefore the motor, does not affect the linear actuator and adjustment of the axial position of the sleeve can be made independent of the rotation. The second element may form part of and / or be formed by the push bar.

[0017] According to one embodiment, the coupling sleeve is arranged concentrically with respect to the planetary gear, with the second element engaging the first element at a location in the center of the sleeve. This arrangement provides a compact and space-saving design. Moreover, such a design further simplifies the arrangement of the required bearings.

[0018] According to one embodiment, the first element is a ball at least partially arranged in the sleeve, and the second element arranged to push the ball is formed by a push bar, whereby an end of the push bar can abut against the rotation bar to displace the sleeve. The ball can be arranged, for example, by press-fitting, at the end of the sleeve facing the linear actuator.

[0019] According to one embodiment, the gear shift assembly further comprises a coupling assembly arranged between the coupling sleeve and the linear actuator, the coupling assembly comprising a first element rotatably coupled to the sleeve, the rotation of the first element being independent of the rotation of the push bar, the push bar being arranged to push the first element axially. This ensures that the rotation of the sleeve, and therefore the motor, does not affect the linear actuator, and adjustment of the axial position of the sleeve can be made independent of the rotation. In one embodiment, the coupling sleeve is arranged concentrically with respect to the planetary gears, the push bar being adapted to engage the first element at a position central to the sleeve. In one embodiment, the first element is a ball at least partially disposed within the sleeve.

[0020] In one embodiment, the joint assembly further comprises a second element translationally coupled to the push bar and adapted to engage the first element, wherein rotation of the first element is independent of rotation of the push bar, and the push bar is arranged to axially push the first element by pushing the second element.

[0021] According to one embodiment, a first axially acting spring means is arranged for biasing the coupling sleeve towards its first position, for example a compression spring arranged to abut against a suitable part of the housing and acting on the second end of the sleeve.

[0022] According to one embodiment, the first and second positions are respectively a first end position and a second end position, between which the coupling sleeve is continuously movable and can be positioned at any position between the first and second end positions. In other words, the push bar of the linear actuator can be positioned at any position between the first and second end positions. Preferably, the position of the push bar can be monitored over the entire range.

[0023] According to one embodiment, the driven member comprises a first engagement portion adapted to engage with a corresponding congruent first portion of the coupling sleeve, and the planetary gear comprises a planetary gear carrier including a second engagement portion adapted to engage with a corresponding congruent second portion of the coupling sleeve. For example, according to one embodiment, at least one of the first and second engagement portions has a polygonal shape, for example including a square or hexagonal cross section.

[0024] According to one embodiment, the planetary gear is the first planetary gear stage. According to one embodiment, the power tool further comprises a front stage gear unit or a second stage gear unit. In such an embodiment, the inventive transmission can be arranged between the motor and the front stage gear unit or the second stage gear unit such that the driven member of the transmission engages with the front stage gear, i.e. is drivingly coupled to the output shaft via the front stage gear. This is advantageous in that the front stage gear unit for such a tool can be an exchangeable front stage gear unit, allowing the front stage gear unit to be exchanged depending on the desired torque while the two-speed transmission remains in or on the tool.

[0025] According to one embodiment, the power tool further comprises a bevel gear arranged between the input shaft and the drive member, the drive member being coupled to the input shaft via the bevel gear, which is advantageous in that due to the change of direction of the transmission mechanism at the bevel gear, a design can be achieved in which the above-mentioned centrally located push rod can be more easily realized.

[0026] According to one embodiment, the linear actuator is a linear motor, for example a DC servo motor with a solid stator housing, a coil assembly, and a multi-pole magnetic push rod.

[0027] According to one embodiment, the linear motor includes at least one internal position sensor configured to sense the position of the push bar, such as an internal Hall sensor, such that the position of the push rod can be continuously determined and monitored. In one embodiment, the linear motor further includes a control unit configured to, for example, monitor and control the movement of the push rod and communicate with an external control unit configured to, for example, control a power tool.

[0028] According to a second aspect of the present invention there is provided a two speed power transmission for a power tool according to any of the above described embodiments comprising planetary gears and a two speed gear shift assembly for directing torque through the planetary gears in a high torque / low drive speed mode or past the planetary gears in a low torque / high drive speed mode, the gear shift assembly comprising a drive member drivingly connected to the input shaft, a driven member drivingly connected to the output shaft, a coupling sleeve arranged to interconnect the drive member and the driven member in a first position and to interconnect the planet gear carrier and the driven member in a second position, and a linear actuator arranged to displace the coupling sleeve between the first and second positions, the linear actuator being a linear actuator comprising a linearly movable push bar arranged to bias the coupling sleeve between the first and second positions.

[0029] The objects, advantages and features of the transmission contemplated within the scope of the second aspect of the present invention will be readily understood from the above discussion of the first aspect of the present invention.

[0030] According to a third aspect of the present invention, there is provided a method of controlling a power tool having planetary gears and a two-speed gear shift assembly using a coupling sleeve and a linear actuator arranged to displace the coupling sleeve to direct torque through the planetary gears in a high torque / low speed drive mode or past the planetary gears in a low torque / high speed drive mode, the method comprising the steps of operating the power tool in a low torque / high speed drive mode of operation in which the coupling sleeve is arranged to direct torque through the planetary gears in a first position, determining when a snug fit has been reached, displacing the coupling sleeve forward by axial movement in a first direction using the linear actuator to reach a second position, and operating the power tool in a high torque / low speed drive mode of operation in which the coupling sleeve is arranged in the second position directing torque through the planetary gears.

[0031] According to one embodiment, the method is a method for a power tool having a two-speed transmission according to any of the above-mentioned embodiments, and includes the steps of operating the tool in a low torque / high speed drive mode of operation with the coupling sleeve disposed in a first position interconnecting the drive member and the driven member, determining that a snug fit has been reached, displacing the coupling sleeve forward by axial movement in a first direction using a linear actuator to reach a second position, and operating the power tool in a high torque / low speed drive mode of operation with the coupling sleeve disposed in the second position interconnecting the planetary gear carrier and the driven member.

[0032] That is, in other words, at the start of rundown (i.e. low torque / high speed mode), the push bar and thus the coupling sleeve are in a first or rearward position where the coupling sleeve couples the drive member and the output shaft. Rundown ends when snug fastening is reached, which is identified, for example, by passing a current limiting threshold. For completeness, "snug fastening" is the point at which the rundown phase transitions to the actual fastening phase. These fastening conditions can be monitored, for example, by an external controller. Thereafter, a signal is sent to the linear motor that rundown is complete, and forward displacement of the push bar and thus the coupling sleeve towards the second position is initiated. Once the coupling sleeve is engaged with the planetary gears, i.e. positioned in the second position, a signal can be sent, for example, to an external controller, indicating that the low speed gear is in position. The final actual fastening phase (i.e. high torque / low speed) can now be initiated.

[0033] According to one embodiment, the step of reaching the second position includes displacing the coupling sleeve rearward by axial movement of the linear actuator in a second opposite direction when the coupling sleeve is not engaged with the planetary gear, rotating the planetary gear, and displacing the coupling sleeve forward by axial movement in a first direction to reach the second position.

[0034] According to one embodiment, the method is a method for a power tool having a two-speed transmission according to any of the above-mentioned embodiments, and the step of reaching the second position further includes the steps of displacing the coupling sleeve rearward by axial movement of the linear motor in a second reverse direction when the coupling sleeve is not engaged with the planetary gear carrier, rotating the drive member, and moving the coupling sleeve forward by axial movement in a first direction by the linear motor to reach the second position.

[0035] That is, if the push bar fails to reach the forward or first position, for example due to a rotational mismatch between the cross section of the sleeve and the corresponding surface of the engaging planetary gear, the direction of axial movement is reversed and the push bar retreats a small distance, possibly at the same time the motor rotates the planetary gear carrier to allow a new position for the coupling sleeve to engage, thereby facilitating the change between the drive modes of the transmission.

[0036] In one embodiment, the method may further include determining when the target torque has been reached and displacing the coupling sleeve axially backward in a second direction by the linear motor back to the first position. That is, the torque may be monitored, for example, by a torque transducer, and when the desired torque is reached, the linear motor receives a signal and returns to engaging the high speed / low torque mode again. This coupling sleeve movement may follow or be combined with motor rotation to aid in proper coupling sleeve engagement as described above.

[0037] The objects, advantages and features of the method contemplated within the scope of the third aspect of the present invention will be readily understood from the above discussion of the second aspect of the present invention.

[0038] Further objects, features and advantages of the present invention will become apparent upon review of the following detailed disclosure, drawings and appended claims. Those skilled in the art will appreciate that different features of the present invention can be combined to create embodiments other than those described below.

[0039] The present invention is described in the following illustrative and non-limiting detailed description of exemplary embodiments with reference to the accompanying drawings. [Brief description of the drawings]

[0040] [Figure 1] 1 is a cross-sectional view of an exemplary power tool including a two-speed power transmission according to one embodiment. [Diagram 2]FIG. 1 is a first perspective view of some of the components of an exemplary transmission according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] All figures are schematic, not necessarily to scale, and generally show only those parts necessary to clarify the invention, other parts may be omitted or merely suggested.

[0042] 1 is a cross-sectional view of a portion of an exemplary power tool, in this case a hand-held fastening tool, according to one embodiment. The fastening tool comprises a housing H, an input shaft IS, a motor coupled to a drive member 2 via a bevel gear 20, an output shaft 1, and a two-speed transmission T disposed between the input and output shafts. Additionally, the fastening tool is connected to an external control unit (described in more detail below when describing the function of this tool) that operates to control the rotational speed of the motor.

[0043] The embodiment of the two-speed power transmission 1 shown in Figure 1 includes planetary gears 4 and a gear shift assembly for directing torque from an input shaft IS to an output shaft 1 via the planetary gears 4 in a high torque / low speed drive mode or past the planetary gears 4 in a low torque / high speed drive mode. The low torque / high speed drive mode of the transmission is shown in Figure 1.

[0044] The planetary gear 4 comprises an internal gear (or gear rim) fixed to the housing H and a planetary gear carrier 41. The transmission assembly comprises a drive member 2, which in the illustrated embodiment forms part of the bevel gear 20, and a driven member 1 drivingly connected to the output shaft 1.

[0045] The coupling sleeve 6 is axially movable between a first position in which the sleeve interconnects the driving member 2 and the driven member 1, i.e. the low torque / high speed mode shown in FIG. 1, and a second position in which the sleeve interconnects the planetary gears 4, and more particularly the planetary gear carrier 4a, and the driven member 1.

[0046] Linear Actuator Ta is , is used to displace the coupling sleeve between the first and second positions, and more particularly, in the illustrated embodiment, a linear DC servo motor comprises a solid stator housing 14, a coil assembly, and a linearly movable multi-pole magnetic push rod 13 arranged to push the coupling sleeve from the first position to the second position. The linear motor further comprises an internal Hall sensor configured to sense the position of the bar 13, and an internal control unit or control board 15. A compression spring 3 is arranged to bias the coupling sleeve 6 towards the first position.

[0047] In the illustrated embodiment, the push bar 13 The joint sleeve 6 and the linear motor Ta and The second element 12 of the coupling assembly is disposed between the first element 12 and the second element 12 of the coupling assembly. .child The coupling assembly further comprises a first element 8 in the form of a ball 8 disposed within the sleeve 6 at a first end 6a thereof and therefore rotating together with the coupling sleeve 6. The rotation of the sleeve 6 causes the rotation of a push bar 13 of the linear motor (and thus the Engage The ball 8 is of an appropriate size to fit into the end 6a of the fitting sleeve 6 and the push bar 13 is arranged to engage (i.e. push) the ball at a position centrally in the sleeve (i.e. via the second element 12).

[0048] The engagement between the coupling sleeve 6 and the driven member 1 (in the first mode) and between the coupling sleeve 6 and the planetary gear carrier 41 (in the second mode) will now be described with reference to FIG. 2, which shows a perspective view of the sleeve 6, the planetary gear carrier 41, the driving member 2 and the driven member 1.

[0049] As can be seen from Figures 1 and 2, the driven member 1 is supported at a first end 1a by a bearing 50 and comprises a first engagement portion 1b at a second end 1b. Similarly, the planetary gear carrier 41 comprises a second engagement portion 41b. These engagement portions 1b and 41b are intended to engage with corresponding first and second portions 6a and 6b of the coupling sleeve 6, the respective interacting surfaces having a congruent shape, in the embodiment shown a hexagonal shape.

[0050] In operation, the power tool of the illustrated embodiment forms part of a system that includes an external control unit (not shown) that operates to control the tool.

[0051] The coupling sleeve 6 is initially biased towards a first position to perform the rundown, i.e. low torque / high speed mode, and the push bar 13 is thus also in a rear position where the coupling sleeve 6 couples the drive member with the output shaft 1 (FIG. 1).

[0052] Rundown ends when a tight fit is reached, which in the illustrated embodiment is determined by the external control unit when a current limit threshold is passed. Once the linear motor receives the signal that rundown is complete, forward displacement of the push bar 13, and therefore the coupling sleeve 6, towards the second position is initiated.

[0053] The position of the push bar 13, and therefore of the coupling sleeve 6, is monitored by an internal Hall sensor, making it possible to determine when the coupling sleeve has engaged with the planet gear, i.e. when the second position has been reached. A signal is sent to an external control device to initiate the final actual fastening phase (i.e. high torque / low speed mode). However, if the respective hexagonal congruent cross sections 6a of the coupling sleeve 6 and the planet gear carrier are not correctly aligned and the sleeve 6 does not engage with the planet gear carrier 41, the linear motor produces a linear motion in the opposite direction (i.e. backwards). The forward motion is then repeated, but combined with a simultaneous slow rotation of the motor and thus the carrier 41, to allow a new position to facilitate engagement. Those skilled in the art will appreciate that the forward motion and rotation can be performed as successive steps as well.

[0054] During final tightening, the torque is monitored by a torque transducer (not shown) and when the desired torque is reached, the linear motor Ta is Upon receiving the signal, the push bar 13 moves rearward to allow the sleeve 6 to re-engage in the high speed / low torque mode. This movement of the coupling sleeve 6 may be combined with simultaneous rotation of the motor to facilitate proper engagement of the coupling sleeve as described above.

[0055] While the present invention has been illustrated and described in detail in the drawings and the above description, such illustration and description must be considered as illustrative or exemplary and not restrictive, and the present invention is not limited to the disclosed embodiments. Those skilled in the art will understand that many modifications, variations and changes are possible within the scope defined in the claims. In addition, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope of the claims. [Explanation of symbols]

[0056] 1 Driven member 2 Driving member 4 Planetary Gears 6 Joint sleeve 13 Pushback - T 2-speed power transmission

Claims

1. A housing (H); An input shaft (IS); An output shaft; A two-speed power transmission (T); A power tool comprising: The two-speed power transmission comprises planetary gears (4) and a two-speed gear shift assembly for directing torque through the planetary gears (4) in a high torque / low speed drive mode or past the planetary gears (4) in a low torque / high speed drive mode; The gear shift assembly includes: A drive member (2) drivingly connected to the input shaft; A driven member (1) drivingly connected to the output shaft; an axially movable coupling sleeve (6) arranged to interconnect the driving member (2) and the driven member (1) in a first position and to interconnect the planetary gear (4) and the driven member (1) in a second position; a linear actuator arranged to displace the coupling sleeve between the first position and the second position; Equipped with the linear actuator comprises a linearly movable push bar (13) arranged to displace the coupling sleeve between the first position and the second position; The gear shift assembly further comprises a coupling assembly arranged between the coupling sleeve and the linear actuator, the coupling assembly comprising a first element (8) rotatably coupled to the sleeve, the rotation of the first element being independent of the rotation of the push bar, the push bar being arranged to push the first element axially; The coupling sleeve is concentrically disposed about the planetary gears, and the push bar is adapted to engage the first element at a central location of the sleeve.

2. The power tool of claim 1 , wherein the first element is a ball at least partially disposed within the sleeve.

3. A power tool according to claim 1 or 2, wherein a first axially acting spring means (3) is arranged to bias the coupling sleeve towards its first position.

4. 4. A power tool according to claim 1, wherein the first and second positions are first and second end positions, and the coupling sleeve is continuously movable therebetween and can be positioned at any position between the first and second end positions.

5. the driven member comprises a first engagement portion (1b) adapted to engage with a corresponding congruent first portion of the coupling sleeve; 5. A power tool according to claim 1, wherein the planetary gear comprises a planetary gear carrier (41) including a second engagement portion (41b) adapted to engage with a corresponding congruent second portion of the coupling sleeve.

6. The power tool of claim 5 , wherein at least one of the first engagement portion and the second engagement portion has a polygonal cross-section.

7. 7. The power tool of claim 1, further comprising a bevel gear disposed between the input shaft and the drive member, the drive member being adapted to be coupled to the input shaft via the bevel gear.

8. 8. The power tool of claim 1, wherein the linear actuator is a linear DC servo motor including a solid stator housing, a coil assembly, and a multi-pole magnetic push rod.

9. The power tool of claim 1 , wherein the linear actuator includes at least one internal position sensor configured to sense a position of the push bar.

10. The power tool according to claim 1 , wherein the planetary gear is a first planetary gear stage.

11. 7. A two-speed power transmission for a power tool according to claim 5 or 6, said transmission comprising planetary gears and a two-speed gear shift assembly for directing torque through said planetary gears in a high torque / low speed drive mode or past said planetary gears in a low torque / high speed drive mode, said gear shift assembly comprising: a drive member drivingly connected to the input shaft; a driven member drivingly connected to the output shaft; a coupling sleeve arranged to interconnect the driving member and the driven member in a first position and to interconnect the planet gear carrier and the driven member in a second position; a linear actuator arranged to displace the coupling sleeve between the first position and the second position; Equipped with the linear actuator comprising a linearly movable push bar (13) arranged to displace the coupling sleeve between the first position and the second position; The gear shift assembly further comprises a coupling assembly arranged between the coupling sleeve and the linear actuator, the coupling assembly comprising a first element (8) rotatably coupled to the sleeve, the rotation of the first element being independent of the rotation of the push bar, the push bar being arranged to push the first element axially; 1. A two speed power variable speed transmission, wherein said coupling sleeve is concentrically disposed about said planetary gears and said push bar engages said first element at a location centrally located on said sleeve.

12. A method for a power tool according to any one of claims 1 to 10, comprising the steps of: operating the power tool in a low torque / high speed drive mode of operation with the coupling sleeve positioned to direct torque through the planetary gears in a first position; determining when a tight fit has been achieved; displacing the coupling sleeve forward by axial movement in a first direction using the linear actuator to reach the second position; operating the power tool in a high torque / low speed drive mode of operation with the coupling sleeve disposed in the second position directing torque through the planetary gears; A method comprising:

13. The step of reaching the second position includes, when the coupling sleeve is not engaged with the planetary gear, displacing the coupling sleeve rearwardly by axial movement of the linear actuator in a second opposite direction; rotating the planetary gears; displacing the coupling sleeve forward by axial movement of the linear actuator in the first direction to reach the second position; The method of claim 12 further comprising:

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