Electromagnetic actuator for power tool

An actuator assembly for a power tool includes an actuator with a permanent magnet. The actuator is moveable between a first position for a first mode of operation, and a second position for a second mode of operation. A first positioning member is adjacent the first position composed of a ferromagnetic material to attract the permanent magnet. A second positioning member is adjacent the second position and composed of a ferromagnetic material to attract the permanent magnet. An electromagnet may be energized to move the actuator between the first position and the second position. When the electromagnet is not energized and the actuator is in the first position, the actuator is retained in the first position. When the electromagnet is not energized and the actuator is in the second position, the actuator is retained in the second position. When the electromagnet is energized, the actuator moves between the first and second positions.

TECHNICAL FIELD

This application relates to an electromagnetic actuator assembly for changing a mode of operation of a power tool.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art. There are various examples of power, tools that include a mode change mechanism that is selectively movable to change a mode of operation of the power tool. Many such power tools include a user actuated mechanical button or switch positioned on the housing to selectively move the mode change mechanism. In other of these power tools, the mode change mechanism may be selectively moveable by another mechanical device in response to a tool condition, e.g., a spring that moves an actuator in response to an output torque.

U.S. Pat. No. 7,452,304, which is incorporated by reference, discloses a power tool with a multi-speed transmission that includes a plurality of planetary gear stages. One or more of the ring gears of the planetary gear transmission are selectively moveable by actuation of a mechanical switch on the housing to selectively engage different sets of planet gears and change the overall speed reduction ratio of the transmission.

U.S. Pat. No. 7,717,192, which is incorporated by reference, discloses a power tool with a selectively moveable collar that changes the mode of operation of the tool between a low speed mode, a high speed mode, and a hammer mode. Rotation of the collar causes movement of a shift pin to change the mode of operation.

U.S. Patent App. Pub. No. 2011/0152029, which is incorporated by reference, discloses a hybrid impact driver and drill with a selector that is selectively moveable to change between an impact mode and a drilling mode, as well as to change a speed setting of the transmission.

U.S. Patent App. Pub. No. 2012/0074658, which is incorporated by reference, discloses a power tool with a tool bit holder integrated into the power tool housing. The housing includes a button or rotational switch that is moveable to move a shifter between a first position that locks a tool bit in the holder and a second position that enables release of the tool bit from the holder.

U.S. Pat. App. Pub. No. 2012/0325509 (to which this application claims priority), which is incorporated by reference, discloses an impact wrench with a socket drive for receiving a socket wrench accessory. The socket drive includes a moveable retaining pin for selectively retaining and releasing the socket wrench accessory from the socket drive. The power tool includes a button or switch for selectively moving the retaining pin to retain the socket wrench accessory on the socket drive or to release the socket wrench accessory from the socket drive.

U.S. Pat. No. 8,347,750, which is incorporated by reference, discloses a power tool with a transmission that includes a radially expanding clutch assembly. The clutch assembly includes a shaft member that can receive an input torque and a gear member that can provide an output torque. The radially expanding clutch assembly also includes a clutch spring that selectively contains rolling members within longitudinal grooves in the shaft member. In the drive condition the rolling members are held in the grooves by the spring, and torque is transmitted from the shaft member to the gear member. In the clutch out condition, the spring expands, allowing the rolling members to move out of the grooves, which interrupts torque transmission from the shaft member to the gear member.

U.S. Pat. No. 7,452,304, which is incorporated by reference, discloses a power tool with a torque clutch having a clutch member that presses a spring against a pin that engages ramps on a face of one of the ring gears. When the output torque overcomes the spring force, the pin rides over the ramps,enabling the ring gear to, rotate, which interrupts torque transmission from the transmission to the output shaft.

SUMMARY

In an aspect, a power tool includes a housing coupleble to a source of electric power, a motor disposed in the housing, an output shaft received at least partially in the housing, and a transmission in the housing and coupled to the motor and the output shaft for transmitting torque from the motor to the output shaft. A mode change mechanism has an actuator, a positioning member, and an electromagnet. The actuator includes a permanent magnet and is moveable between a first position for a first mode of operation of the power tool, and a second position a second, different mode of operation of the power tool. The positioning member and the electromagnet are configured to (i) retain the actuator in the first position when the electromagnet assembly is not energized and the actuator is in the first position, (ii) retain the actuator in the second position when the electromagnet assembly is not energized and the actuator is in the second position, and (iii) move the actuator from one of the first position and the second position to the other of the first position and the second position when the electromagnetic assembly is momentarily energized.

Implementations of this aspect may include one or more of the following features. The positioning member may include a second permanent magnet adjacent to the first position, and stationary relative to the actuator, wherein the actuator permanent magnet and the second permanent magnet are configured to attract when the actuator is in the first position and repel when the actuator is in the second position. The actuator permanent magnet and the second permanent magnet may each include an array of permanent magnets, with a portion of each array arranged to exert an attractive force between actuator permanent magnet and the second permanent magnet, and a remaining portion of each array of the permanent magnets arranged to exert a repulsive force between actuator permanent magnet and the second permanent magnet. The electromagnet may be momentarily energized by current flowing in a first direction to move the actuator from the first position to the second position, and can be momentarily energized by current flowing in a second opposite direction to move the actuator from the second position to the first position. A stop may prevent contact between the actuator and the positioning member when the actuator is in the first position.

The positioning member may include a first positioning member adjacent the first position and composed of a ferromagnetic material to attract the permanent magnet when the actuator is in the first position, and a second positioning member adjacent the second position and composed of a ferromagnetic material to attract the permanent magnet when the actuator is in the second position. The electromagnet may include a first electromagnet adjacent to the first position and a second electromagnet adjacent to the second position, such that when one of the first electromagnet and the second electromagnet is energized, the actuator moves from the first position to the second position, and when the other of the first electromagnet and the second electromagnet is energized, the actuator moves from the second position to the first position. A control circuit may be configured to control energization of the first and second electromagnets in response to an input condition, the input condition comprising one of a user selection of a desired power tool operating condition and a sensed power tool operating condition.

The actuator, the positioning member, and the electromagnet may comprise a portion of a clutch. The clutch may have an input member coupled to the transmission, an output member coupled to the output shaft, and a coupling device movable between a driving position in which torque is transmitted from the input member to the output member and a clutching position in which torque transmission from the input member to the output member is interrupted, and wherein when the actuator is in the first position. The actuator may retain the coupling member in the driving position, and when then actuator is in the second position, the actuator may allow the coupling member to move to the clutching position. The input member may have an input sleeve defining a radial bores, the output member may have an output cylinder received in the input sleeve defining a groove, the coupling member may have a drive ball received in the bore. The actuator may include a actuation sleeve received over the input sleeve, wherein when the actuation sleeve is in the first position, the ball is retained in the groove to transmit torque from the input sleeve to the output cylinder, and when the actuation sleeve is in the second position, the ball is permitted to escape the groove to interrupt torque transmission, from the input sleeve to the output cylinder. The input member may include a ring gear of the transmission having a recess, the output member may have a portion of the output shaft, the actuator may have a sleeve, and the coupling member may have a leg extending from the sleeve. When the sleeve is in the first, position, the leg may engage the recess, to inhibit rotation of the ring gear, which enables torque transmission to the output member, and when the sleeve is in the second position, the leg, does not engage the recess to allow rotation of the ring gear, which, interrupts torque transmission to the output member.

The actuator, the positioning member and the electromagnet comprise a portion of a tool holder. The tool holder may be coupled to the output shaft for releasably retaining a power tool accessory. When the actuator is in the first position, the accessory is retained by the tool holder. When the actuator is in the second position the accessory is releasable from the tool holder. The tool holder may include a socket drive having a retractable retention pin and a linkage coupled to the retention pin for selectively retracting the retention pin. The actuator may include a ring configured to move the linkage and the retention pin between a retention position and a release position when the actuator is in the first position and the second position, respectively.

In another aspect, a mode change mechanism for a power tool includes an actuator that includes a permanent magnet and that is moveable between a first position for a first mode of operation of the power tool, and a second position a second, different mode of operation of the power tool. A first positioning member adjacent, the first position is composed of a ferromagnetic material to attract the permanent magnet when the actuator is in the first position. A second positioning member adjacent the second position is composed of a ferromagnetic material to attract, the permanent magnet when the actuator is in the second position. An electromagnet is configured to be energized to move the actuator between the first position and the second position, wherein (i) when the electromagnet is not energized and the actuator is in the first position, the actuator is retained in the first position, (ii) when the electromagnet is not energized and the actuator is in the second position, the actuator is retained in the second position, and (iii) when the electromagnet is energized, the actuator moves from one of the first and second positions to the other of the first and second positions.

Implementations of this aspect may include one or more of the following features. The electromagnet may include a first electromagnetic coil adjacent the first position, and a second electromagnetic coil adjacent the second position. The first electromagnetic coil may be energized to create a magnetic force to move the permanent magnet and the actuator away from the first positioning member to the second position, and the second electromagnetic coil may be energized to create a magnetic force to move the permanent magnet and the actuator away from second positioning member and to the first position. The electromagnet may be energized to cause current to flow in a first direction creating a magnetic force to move the permanent magnet and the actuator away from the first positioning member and to the second position, and the electromagnet may be energized to cause current to flow in a second opposite direction creating a magnetic force to move the permanent magnet and the actuator away from the second positioning member and to the first position. A first stop may prevent contact between the actuator and the first positioning member when in the first position, and a second stop may prevent contact between the actuator and the second positioning member when in the second position.

In another aspect, a method of operating a mode change mechanism of a power tool includes the following. It is determined whether the power tool should be operating in a first mode of operation or a second mode of operation. It is determined whether an actuator that includes a permanent magnet is in a first position that causes the power tool to operate in the first mode of operation or a second position that causes the power tool to operation in the second mode of operation. An electromagnet is energized to cause the actuator and the permanent magnet to move between the first position and the second position if the actuator is in the first position and the power tool should be operating in the second mode of operation, or if the actuator is in the second position and the power tool should be operating in the first mode of operation. The actuator is retained, without energizing the electromagnet, in the first position if the actuator is in the first position and the power tool should be operating in the first mode of operation, or in the second position if the actuator is in the second position and the power tool should be operating in the second mode of operation.

Implementations of this aspect may include one or more of the following features. Retaining the actuator may include providing a first ferromagnetic positioning member adjacent the first position to attract the permanent magnet when the actuator is in the first position, and providing a second ferromagnetic positioning member adjacent the second position to attract the permanent magnet when the actuator is in the second position. Energizing the electromagnet may include energizing a first electromagnetic coil adjacent the first position to create a magnetic force that moves the permanent magnet and the actuator away from the first position to the second position when the actuator is in the first position and should be in the second position, and energizing a second electromagnetic coil adjacent the second position to create a magnetic force that moves the permanent magnet and the actuator away from the second position to the first position when the actuator is in the second position and should be in the first position. Energizing the electromagnet may include causing current to flow through the electromagnet in a first direction to create a magnetic force that moves the permanent magnet and the actuator away from the first position to the second position when the actuator is in the first position and should be in the second position, and causing current to flow through the electromagnet in a second opposite direction to create a magnetic force that moves the permanent magnet and the actuator away from the second position to the first position when the actuator is in the second position and should be in the first position.

Advantages may include one or more of the following. The mode change mechanism can he moved by applying a brief impulse of electrical energy. In this way, the user actuated switch or button may be replaced with an electronic switch and may be positioned on the tool housing at virtually any location. Alternatively, the user actuated switch could be replaced with an automated circuit for determining when to move the actuator based on one or more input conditions (e.g., proximity to workpiece, output torque, current delivered to motor, etc.). Also, heavy mechanical switches can be eliminated which may reduce the overall size, weight, and complexity of the power tool. These and other advantages and features will be apparent from the description, the drawings and the claims.

DETAILED DESCRIPTION

Referring toFIGS. 1-3, in an embodiment, a mode change mechanism in the form of an electromagnetic clutch assembly100may replace the radially expanding clutch assembly in the power tool disclosed in the above-referenced U.S. Pat. No. 8,347,750. The clutch assembly100includes an input shaft102and an output shaft104. The input shaft102is fixedly attached to a positioning member in the form of a hollow input sleeve106. The output shaft104is fixedly attached to an output cylinder108that is received inside the input sleeve106. The input sleeve includes a plurality of radial bores110that receive a plurality of drive balls112. The output cylinder108have a plurality of longitudinal grooves113that receive the drive balls114. The input sleeve106has a reduced diameter portion111with a rear shoulder103and a front shoulder105. Received over the reduced diameter portion111of the input shaft102and over the input sleeve106is an actuator in the form of an actuation sleeve114. The actuation sleeve114has a base wall119and a cylindrical wall115with an internal surface having a first substantially flat portion116and a second ramped portion118.

The actuation sleeve114is selectively moveable between a first position for a first mode of operation (FIG. 2) where the base wall119abuts the front shoulder105and the flat portion116engages the balls112to retain the balls in the grooves113of the output cylinder108, and a second position for a second mode of operation (FIG. 3) where the base wall119abuts the rear shoulder103and the ramped portion118engages the balls112to allow the balls to escape the grooves113of the output cylinder108. In the first mode of operation, when the balls112are retained in the grooves113, torque is transmitted from the input shaft102to the output shaft104. In the second mode of operation, when the balls112escape the grooves113, torque transmission from the input shaft102to the output shaft104is interrupted.

To facilitate moving the actuation sleeve114between the first position and the second position, the actuation sleeve114has a base wall119that includes a first plurality of magnets120arranged in a first array126. The input sleeve106also has a base wall122with a second plurality of magnets124arranged in a second array128. Some opposing pairs of magnets from the first array126and the second array128are arranged with opposite poles facing one another (i.e., north facing south or south facing north) so that they are configured to attract one another. Other opposing pairs of magnets from the first array126and the second array128are arranged with the same poles facing one another (i.e., north facing north or south facing south) so that they are configured to repel one another. Such magnet arrays enable the magnet arrays to have varying attractive and repulsive properties depending on the relative distance and positions of the magnet arrays. Similar magnet arrays may also be known as coded patterns of magnetic elements or correlated magnets. Similar magnet, arrays, are described, e.g., in U.S. Pat. No. 7,750,778, which is incorporated by reference, and are sold by Correlated Magnetics Research, located in New Hope, Ala.

Referring also toFIG. 4, the first magnet array126and the second magnet array128are configured so that the sum of the attractive force of the magnets arranged to attract one another and the repulsive force of the magnets arranged to repel one another varies according to the separation distance between the first array126and the second array128.FIG. 4illustrates the attractive force vs. separation distance for the magnets arranged to attract (curve A), the repulsive force vs. separation, distance for the magnets arranged to repel (curve R), and the net attractive or repulsive force of all of the magnets vs. distance (curve T). The net force is strongly positive (attractive) when the separation distance is less than a predetermined threshold (e.g., 1 mm), and the net force is weakly negative (repulsive) when the separation distance is greater than the predetermined threshold.

The clutch assembly100also has an electromagnet130in the form of a coil of wire132wrapped around a portion of the input shaft102adjacent to the actuation sleeve114. When the actuation sleeve is in the second position (FIG. 3), the electromagnet130can be energized by driving current in a first direction, which generates a magnetic field that repels the first array126of magnets with a force greater than the repulsive force between the first array126and second array128of magnets. This tends to push the actuation sleeve114to the first position (FIG. 2). When the actuation sleeve is in the first position (FIG. 2), the electromagnet130can be energized by driving current in a second opposite direction. Which generates a magnetic field that attracts the first array of magnets126with a force greater than the attractive force between the first array126and the second array128. This tends to pull the actuation sleeve to the second position (FIG. 3).

Referring, also toFIG. 5, the electromagnet130may be coupled to an electronics module138that includes a driver circuit140(e.g., an H-bridge circuit) configured to drive the electromagnet130. The driver circuit140may be connected to the output of a control circuit142(e.g., a microprocessor or controller). The control circuit142may receive an input from a torque setting circuit144(e.g., from a user input and/or from a pre-programmed memory device)) that generates a signal corresponding to a desired torque setting. The control circuit142may also receive an input from a torque sensing circuit146that generates a signal that corresponds to the amount of output torque on the tool. The torque sensing circuit may include one or more of a current sensor, a position sensor, a torque transducer, a force sensor, etc. In one possible embodiment, the torque sensing circuit is similar to the electronic clutch circuit described in commonly owned U.S. patent application Ser. No. 13/798,210, filed Mar. 13, 2013, which is incorporated by reference. In addition, the control circuit may receive an input signal from a position sensing circuit148, which corresponds, the current position of the actuation sleeve118(e.g., via a Hall effect sensor or a membrane potentiometer). The controller processes the torque setting input signal, the torque sensing input signal, and the position sensing input signal to determine when and, in which direction to cause the drive circuit to energize the electromagnet to change the position of the actuation sleeve118.

Referring also toFIG. 6, in use, first, at step150, the control circuit receives an input signal from the torque setting circuit that corresponds to the desired torque setting. At step152, the control circuit receives an input signal from the torque sensing circuit that indicates the output torque. At step154, the control circuit receives an input signal from the position sensing circuit that indicates whether the actuation sleeve118is in the first position or the second position. At step156, the control circuit determines whether the sensed torque has exceeded the desired threshold torque, which indicates that torque transmission should be interrupted. If YES, then at step158, the control circuit determines whether the actuator is already in the second position (FIG. 3), in which torque transmission is interrupted. If YES, then control circuit returns to step150. If NO, then the control circuit causes the drive circuit to momentarily drive the electromagnet to attract the actuator from the first position to the second position to interrupt torque transmission. Once the actuator is in the second position, current need not be delivered to the electromagnetic coil to keep the actuator in the second position, as the repulsive force between the first and second magnet arrays will keep the actuator in the second position. By requiring only a momentary burst of current, this saves energy and drain on a battery (if a cordless tool).

If at step156, the control circuit determines that the sensed torque does not exceed the torque setting, this indicates that torque transmission should be permitted. Next, at step158, the control circuit determines whether the actuator is already in the first position (FIG. 2), in which torque transmission is permitted. If YES, then control circuit returns to step150. If NO, then the control circuit causes the drive circuit to momentarily drive the electromagnet to repel the actuator away from the second position to the first position to allow torque transmission. Once the actuator is in the first position, current need not be delivered to the electromagnetic coil to keep the in the second position, as the attractive force between the first and second magnet arrays will keep the actuator in the second position. By requiring only a momentary burst of current, this saves energy and drain on a battery (if a cordless tool).

Referring toFIGS. 7-9, in another embodiment, a mode change mechanism in the form of an electromagnetic clutch assembly700may replace the torque clutch assembly in the power tool disclosed in the above-referenced U.S. Pat. No. 7,452,304. The clutch assembly700includes a ring gear702of the planetary transmission, and a positioning member in the form of a generally cylindrical transmission housing704. The transmission housing704receives the ring gear702and other gears of the planetary gear transmission (not shown), and is fixedly received in a tool housing706. The transmission housing704includes a plurality of radial bores710that receive a plurality of drive balls712. The ring gear702has a plurality of longitudinal grooves713that receive the drive balls712. Received at least partially over the ring gear702is an actuator in the form of an actuation sleeve714. The actuation sleeve714has a base wall719and a cylindrical wall715with an internal surface having a first substantially flat portion716and a second ramped portion718. The tool housing706has a rear internal shoulder703. The transmission housing704has a front internal shoulder705.

The actuation sleeve714is selectively moveable between a first position (FIG. 8) where the base wall719abuts the front shoulder705and the flat portion716engages the bails712to retain the balls in the grooves714of the ring gear702, and a second position (FIG. 9) where the base wall719abuts the rear shoulder703and the ramped portion718engages the balls712to allow the balls to escape the grooves714of the ring gear702. In the first position (FIG. 8), when the balls712are retained in the grooves714, the ring gear702is not permitted to rotate relative to the transmission housing704, which allows torque to be transmitted from the transmission to an output shaft (not shown), as will be understood to those of ordinary skill in the art. In the second position (FIG. 9), when the balls712escape the grooves714, and the ring gear702is permitted to rotate freely relative to the transmission housing704, which interrupts torque transmission from the transmission to the output shaft, as will be understood to those of ordinary skill in the art.

To facilitate moving the actuation sleeve714between, the first position and the second position, the actuation sleeve714has a base wall719that includes a first array of magnets726, and the transmission housing704has a second array of magnets728that are arranged similarly to the first array of magnets126and the second array of magnets128described above with respect toFIGS. 1-4. Therefore, the first magnet array726and the second magnet array728are configured so that the net magnetic force is strongly positive (attractive) when the separation distance is less than a predetermined threshold (e.g., 1 mm), and the net magnetic force is weakly negative (repulsive) when the separation distance is greater than the predetermined threshold.

The clutch assembly700also has an electromagnet730in the form of a coil of wire732adjacent to the actuation sleeve714, similar to the electromagnet130described above with respect toFIGS. 1-4. Thus, when the actuation sleeve is in the second position (FIG. 9), the electromagnet730can he momentarily energized by driving current in a first direction, to push the actuation sleeve714to the first position (FIG. 8). When the actuation sleeve is in the first position (FIG. 8), the electromagnet730can be momentarily energized by driving current in a second opposite direction, to pull the actuation sleeve714to the second position (FIG. 9). The electromagnet730may be coupled to a similar electronics module as the electronics module138illustrated inFIG. 5and described above. The clutch assembly700may be operated according to the method illustrated inFIG. 6and described above.

Alternatively, it is known, e.g. from the aforementioned U.S. Pat. No. 7,452,304 and related art, that the speed reduction ratio of a multi-speed planetary transmission may be changed by selectively preventing rotation of one or more of the ring gears (which results in a greater speed reduction) or allowing rotation of one or more of the ring gears (which results in a lesser speed reduction). Therefore, the clutch assembly700could instead be connected to a controller that receives an input of a speed setting signal that corresponds to a desired speed setting of the tool. When the speed setting signal changes, indicating that the desired speed reduction ratio has changed, the electromagnet730can be driven to move the actuation sleeve714to either the first or second position to change the speed reduction ratio of the transmission accordingly.

Referring toFIG. 10, in the above mode change mechanisms100,700, or in any other power tool mode change mechanisms, an actuator1020may be moveable between first and second positions and a positioning member1022may remain stationary relative to the actuation1020. The, actuator1020may have a first magnet array1026(which is a substitute for the above-described magnet arrays126,726) and the positioning member1022may have a second magnet array1028(which is a substitute for the above-described magnet arrays128,728). The first magnet array1026includes a first inner ring magnet1032and a first outer ring magnet1030concentrically mounted on a first non-magnetic hacker plate1034. Both the first inner and first outer ring magnets1032,1030are arranged with their north poles facing toward the second magnet array1028. The second magnet array1028includes a second inner ring magnet1038and a second outer ring magnet1036concentrically mounted on a second non-magnetic backer plate1040. The second outer ring magnet1036is arranged with its south pole facing the north pole of the first outer ring magnet1030so as to provide an attractive force. The second inner ring magnet1038is arranged with its north pole facing the north pole of the first inner ring magnet1032so as to provide a repulsive force. The first and second ring magnet arrays1026,1028together provide a net force vs. separation distance profile as the profile shown inFIG. 4. Thus, the actuator1020and the positioning member1022may be used in conjunction with an electromagnet (not shown) in the manner discussed above with respect toFIGS. 1-9to enable movement of the actuator between the first and second positions for first and second modes of operation when the electromagnet is energized, and allows the actuator to be retained in one of the first and second positions when the electromagnet is not energized.

Referring toFIGS. 11-14, in another embodiment, a power tool such as a drill/driver1180includes a mode change mechanism in the form of an electromagnetic clutch assembly1100. The power tool1180includes a housing1182having a motor housing1181, a handle1182extending downward from the motor housing1181, and a transmission housing1184coupled to a front end of the motor housing1181. The handle1182is coupleable to a removable battery pack1186, although it should be understood that the battery could be integral, or the housing could be coupled to an alternative source of electrical power such as an AC power source. Disposed in the motor housing1181is a motor1186and a control circuit1188, which in turn is coupled to the battery pack1186and to a trigger switch1190disposed on the housing1182. The motor1186is coupled to a transmission1192, which transmits torque from the motor1186to a spindle1194. The spindle1194is coupled to a tool bit holder1196extending from the housing for removably retaining a tool bit such as a screwdriver bit. In use, actuation of the trigger switch1190causes the controller to deliver electrical power to the motor1186, which in turn drives the transmission1192, the spindle1104, and the tool bit holder1196.

Referring toFIGS. 12-14, the electromagnetic clutch assembly1100includes an output stage ring gear1102of the transmission1192, the output spindle1104, and an axially moveable actuator in the form of an actuator sleeve1106. The ring gear meshes with a plurality of planet gears (not shown) which arc carried by an'output stage planet carrier1108. The carrier1108is non-rotationally coupled with the output spindle1104. The planet gears also mesh with an input sun gear (not shown) that extends from the motor or from a previous stage of the transmission. When the ring gear1102is held stationary or grounded relative to the transmission housing1184, rotation of the sun gear causes the planet gears to orbit the sun gear, which causes the planet carrier1108to rotate and drive the output spindle1104in rotation. When the ring gear1102is not grounded or allowed to rotate relative to the housing, rotation of the sun gear causes the planet gears to spin on their axis but not to orbit the sun gear, so that the carrier1108, and thus, the spindle1104do not rotate. Therefore, selectively grounding the ring gear1102acts as a clutch which prevents torque transmission when the ring gear1102is not grounded, and allows torque transmission when the ring gear1102is grounded.

The ring gear1102includes a plurality of axial slots1110facing the actuator sleeve1106. The actuator sleeve1106has a ring portion1112and a plurality of legs1114extending axially from the actuator sleeve1106toward the ring gear1102. Each leg1114terminates in a tooth1116configured to engage one of the slots1110in the ring gear1102. The actuator sleeve is rotationally fixed relative to the housing, and is moveable axially between a first position for a first mode of operation (FIG. 1) and a second position for a second mode of operation (FIG. 14). In the first mode of operation (FIG. 13), the teeth1116of the actuator1106engage the slots1110in the ring gear1102, preventing rotation of the ring gear, which allows torque to be transmitted from the transmission to the output spindle1104. In the second mode of operation (FIG. 14), the teeth1116of the actuator1106do not engage the slots1110in the ring gear1102, which allows the ring gear1102to rotate, thus interrupting torque transmission to the output spindle1104.

To facilitate moving the actuation sleeve1106between the first position and the second position, the actuation sleeve1106includes a ring-shaped permanent magnet1118coupled to the ring portion1112of the actuation sleeve1106. In addition, received in a rear portion1124of the transmission housing1184is a first positioning member1125having a first ferromagnetic ring1126and a first ring-shaped electromagnet1128. Received in the front portion1120of the transmission housing1184is a second positioning member1127having a second ferromagnetic ring1120and a second ring-shaped electromagnet1122. When the actuation sleeve1106is in the first position (FIG. 13) and neither electromagnet1122,1128is actuated, the actuation sleeve1106tends to stay in the first position due to the attractive force between the ring magnet1118and the first ferromagnetic ring1126being greater than the attractive force between the ring magnet1118and the second ferromagnetic ring1120(due to the closer proximity to the first ferromagnetic ring1120).

To move the actuation sleeve1106to the second position (FIG. 14), the first electromagnet1128can be momentarily energized to create a repulsive force against the ring magnet1118and/or the second electromagnet1120can be momentarily energized to generate an attractive force with the ring magnet1118, with the sum of these forces being greater than the attractive force between the ring magnet1118and the first ferromagnetic ring1126. Once these forces cause the actuator sleeve1106to move to the second position (FIG. 14), the electromagnets1122,1128can be de-energized, and the actuator sleeve1106will remain in the second position due to the attractive force between the ring magnet1118with the second ferromagnetic ring1120being greater than the attractive force between the ring magnet1118and the first ferromagnetic ring (due to closer proximity to the second ferromagnetic ring1120).

To return the actuation sleeve1106to the first position (FIG. 13), the first electromagnet1128can be momentarily energized to create an attractive force with the ring magnet1118and/or the second electromagnet1120can he momentarily energized to generate a repulsive force against the ring magnet1118, with the sum of these forces being great than the attractive force between the ring magnet1118and the second ferromagnetic ring1120. Once these forces cause the actuator sleeve1106to move to the first position (FIG. 13), the electromagnets1122,1128can be de-energized, and the actuator sleeve1106will remain in the first position, as discussed above. The transmission housing may also include mechanical stops1130and1132in front of each of the ferromagnetic rings1120,1126to prevent complete contact between the ring magnet1118and the ferromagnetic rings1120,1126, in order to require less force to move the actuator sleeve1106between the first and second positions.

Referring also toFIG. 15, the electromagnets1122,1128each may be coupled to an electronics module1150that includes a driver circuit1152(e.g., an H-bridge circuit) configured to drive the electromagnets1122,1128. The driver circuit1158may be connected to the output of the control circuit1188(e.g., a microprocessor or controller). The control circuit1188may receive an input from a torque setting circuit1154that generates a signal corresponding to a desired torque setting. The desired torque setting may be input from a user interface1148(e.g., buttons or electronic controls) coupled to the housing. The control circuit1188may also receive an input from a torque sensing circuit1156that generates a signal that corresponds to the amount of output torque on the tool. The torque sensing circuit1156may include one or more of a current sensor, a position sensor, a torque transducer, a force sensor, etc. In one possible embodiment, the torque sensing circuit is similar to the electronic clutch circuit described in the aforementioned commonly owned U.S. patent application Ser. No. 13/798,210, filed Mar. 13, 2013, which is incorporated by reference.

The control circuit1188may also receive an input from a distance setting circuit1160. The distance setting circuit1160that generates a signal corresponding to a desired distance from the workpiece at which the electromagnetic clutch should interrupt torque transmission. The desired distance setting may be input from the user interface1148. The control circuit1188also receives an input from a distance sensing circuit1146that generates a signal that corresponds to a sensed distance between the tool and the workpiece. The distance sensing circuit is coupled to a proximity sensor system1140that includes a optical generator (e.g., an LED, light or laser generator)1142and an optical, detector1144. Based on input from the optical detector1144corresponding to the intensity of light reflected from the workpiece, the distance sensing, circuit1146generates a signal that corresponds to the sensed distance from the workpiece. Other optical and non-contact devices may be used to sense distance from a workpiece.

The user interface may also enable the user to select between a distance sensing mode of operation and a torque sensing mode of operation. In addition, the control circuit may receive an input signal from a position sensing circuit1158, which corresponds the current position of the actuation sleeve1106(e.g., via a Hall effect sensor or a membrane potentiometer). The controller processes the torque setting input signal, the torque sensing input signal, the distance setting input signal, the distance sensing input signal, and the position sensing input signal to determine when and in which direction to cause the drive circuit to energize the electromagnets to change the position of the actuation sleeve1106.

Referring toFIG. 16A, in use, at step1200, the control circuit first receives a user input of whether to use the distance sensing mode or the torque sensing mode. If the distance sensing mode is selected, the control circuit performs the steps illustrated inFIG. 16B, as described below. If the torque sensing mode is selected, then at step1201, the control circuit receives the input signal from the torque setting circuit that corresponds to the desired torque setting. At step1202, the control circuit receives the input signal from the torque sensing circuit that indicates the output torque. At step1204, the control circuit receives the input signal from the position sensing circuit that indicates whether the actuator is in the first position or the second position. At step1206, the control circuit determines whether the sensed torque has exceeded the desired threshold torque, which indicates that torque transmission should be interrupted. If YES, then at step1208, the control circuit determines whether the actuator is already in the second position (FIG. 14), in which torque transmission is interrupted. If YES, then control circuit returns to step1201. If NO, then at step1210, the control circuit causes the drive circuit to momentarily drive the electromagnets to move the actuator sleeve from the first position to the second position to interrupt torque transmission. Once the actuator sleeve is in the second position, current need not be delivered to the electromagnets to keep the actuator sleeve in the second position, as the attractive force between the permanent magnet ring and the second ferromagnetic ring will do this. By requiring only a momentary burst of current, this saves energy and drain on a battery (if a cordless tool).

If, at step1206, the control circuit determines that the sensed torque does not exceed the torque setting, this indicates that torque transmission should be permitted. Next, at step1212, the control circuit determines whether the actuator is already in the first position (FIG. 13), in which torque transmission is permitted. If YES, then control circuit returns to step1201. If NO, then, at step1214, the control circuit causes the drive circuit to momentarily drive the electromagnets to move the actuator sleeve away from the second position to the first position to allow torque transmission. Once the actuator sleeve is in the first position, current need not be delivered to the electromagnets to keep the sleeve in the first position, as the attractive force between the permanent ring magnet and the first ferromagnetic ring will keep the sleeve in the first position. By requiring only a momentary burst of current, this saves energy and drain on a battery (if a cordless tool).

Referring toFIG. 16B, if, at step1200inFIG. 16A, the distance sensing mode is selected, then at step1301, the control circuit receives the input signal from the distance setting circuit that corresponds to the desired distance setting for when to interrupt torque transmission. At step1302, the control circuit receives the input signal from the distance sensing circuit that indicates the sensed distance of the tool holder from the workpiece. At step1304, the control circuit receives the input signal from the position sensing circuit that indicates whether the actuator sleeve is in the first position or the second position. At step1306, the control circuit determines whether the sensed distance is less than the desired threshold distance, which indicates that torque transmission should be interrupted. If YES, then at step1308, the control circuit determines whether the actuator is already in the second position (FIG. 14), in which torque transmission is interrupted. If YES, then control circuit returns to step1301. If NO, then at step1310, the control circuit causes the drive circuit to momentarily drive the electromagnets to move the actuator sleeve from the first position to the second position to interrupt torque transmission. Once the actuator sleeve is in the second position, current need not be delivered to the electromagnets to keep the actuator sleeve in the second position, as the attractive force permanent magnet ring and the second ferromagnetic ring will do this. By requiring only a momentary burst of current, this saves energy and drain on a battery (if a cordless tool).

If, at step1306, the control circuit determines that the sensed distance is not less than the distance setting, this indicates that torque transmission should be permitted. Next, at step1312, the control circuit determines whether the actuator is already in the first position (FIG. 13), in which torque transmission is permitted. If YES, then control circuit returns to step1301. If NO, then, at step1314, the control circuit causes the drive circuit to momentarily drive the electromagnets to move the actuator sleeve away from the second position to the first position to allow torque transmission. Once the actuator sleeve is in the first position, current need not be delivered to the electromagnets to keep the sleeve in the first position, as the attractive force between the permanent ring magnet and the first ferromagnetic ring will keep the sleeve in the first position. By requiring only a momentary burst of current, this saves energy and drain on a battery (if a cordless tool).

Referring toFIGS. 17-20, in another embodiment, a power tool such as an impact wrench1710includes an electromagnetic mode change mechanism in the form of an electromagnetically actuatable, socket holder1720. The impact wrench1710includes a housing1712having a handle1714, a trigger mechanism1716for activating the impact wrench1710, and a cover1760at a front of the housing1712. A base1715of the handle1714is adapted to receive a battery pack (not shown) for use as a cordless impact wrench. It should be understood that the present disclosure can also be applied to pneumatic, hydraulic and corded electrical impact wrench devices. The impact wrench includes a motor1711disposed within the housing1712that drives a transmission and impact mechanism1713, which in turn drives an anvil1718extending from the front end of the housing1712, as is generally known in the art, and as described in the aforementioned U.S. patent application Ser. No. 13/494,325. The anvil1718includes a square socket drive1718athat is designed to drive a socket wrench (not shown).

The mode change mechanism in the form of the electromagnetically actuatable socket holder1720is configured to selectively retain a socket wrench on the square drive1718a.The socket holder1720includes a radially extending and retractable retainer pin1724configured to engage the socket wrench when it is coupled to the square socket drive1718a.The retainer pin1724is received in a radial aperture1723in a distal end of the square socket drive1718a.A lever pin1730is received in an axially extending bore1732provided in the anvil1718. The lever pin1730has a rear end portion with a partially spherical pivot end1750received in a concave partially conical bore portion1732aof the bore1732. The lever pin1730also has a front end portion that engages a transverse aperture1734provided in the retention pin1724. In addition, the lever pin1730has a mid portion that engages a transverse aperture in art actuator pin1748. The actuator pin1748is received in a transverse bore1727in a proximal portion of the anvil1718. The actuator pin1748is biased to a radially outward direction by a spring1726that is received in the transverse bore1727.

Disposed inside of the cover1760is an actuator in the form of an axially moveable cam ring1740, a first positioning member in the form of an axially stationary forward ring1762, and a second positioning member in the form of an axially stationary rearward ring1764. The cam ring1740has an inner ear surface1746disposed against an outer earn surface1744of the actuator pin1748The cam ring is moveable between a forward position for a first mode of operation (FIG. 18A) and a rearward position for a second mode of operation (FIG. 18B). The forward ring1762includes a forward electromagnetic <coil1766disposed in a first annular ferromagnetic (e.g., steel) cup1768. The rearward ring1764includes a rearward electromagnetic coil1770disposed in a second annular ferromagnetic (e.g., steel) cup1772. The cam ring1740is disposed between the for card and rearward rings1762,1764and includes an integral permanent magnet ring1742.

The forward and rearward electromagnetic coils1766,1770may be selectively energized to move the cam ring1740between its forward or rearward position. To move the cam ring1740to its rearward position (FIG. 18B), the front electromagnet1766can be momentarily energized to create a repulsive force against the ring magnet1742and/or the rear electromagnet1770can be momentarily energized to generate an attractive force with the ring magnet1742, with the sum of these forces being greater than the attractive force between the ring magnet1742and the first ferromagnetic cup1768. Once these forces cause the cam ring1742to move to the rearward position (FIG. 18B), the electromagnets1766,1770can be de-energized, and the cam ring1742will remain in the rearward position due to the attractive force between the ring magnet1742with the second ferromagnetic cup1772being greater than the attractive force between the ring magnet1742and the first ferromagnetic cup1768(due to closer proximity to the second ferromagnetic cup1772).

To return the cam ring1740to the first position (FIG. 18A), the forward electromagnet1766can be momentarily energized to create an attractive force with the ring magnet1742and/or the rearward electromagnet1770can be momentarily energized to generate a repulsive force against the ring magnet1742, with the sum of these forces being greater than the attractive force between the ring magnet1742and the rearward ferromagnetic, cup1772. Once these forces cause the cam ring1742to move to the first position (FIG. 18A), the electromagnets1766,1770can be de-energized, and the cam ring1740will remain in the forward position due to the attractive force between the ring magnet1742and the first ferromagnetic cup1768being greater than the attractive force between the ring magnet1742and the second ferromagnetic cup1772(due to the closer proximity to the first ferromagnetic cup1768).

Once in the forward or rearward positions the permanent magnet1742is attracted to the first annular cup1768if in the forward position, or the second annular cup1772if in the second position. Thus only a pulse of energy is required to change the position of the cam ring1740and thus the mode of operation. Continuous power is not required to hold the cam ring in either the forward or rearward position and this is advantageous for energy conservation on a cordless tool. Further, it should be understood that the electromagnetically actuatable socket holder1720can be operated using a single coil and a spring for biasing the earn ring away from the coil during a non-activated state. The cover1760may also include mechanical stops (not shown) between each of the ferromagnetic cups1768,1772and the ring magnet1742to prevent complete contact between the ring magnet1742and the ferromagnetic cups1768,1768, in order to require less force to move the cam ring1740between the forward and rearward positions.

When the electromagnets cause the cam ring1746to move to its rearward position in the second mode of operation (FIG. 18B), the cam surface1746of the cam ring1724engages the cam surface1744of the actuator pin1748, causing the actuator pin1748to move downward in the bore1727in the anvil1718against the biasing force of the spring1726. As the actuator pin1748is moved downward, the lever pin1732pivots in a counter clockwise direction CCW about pivot end1750, causing the retainer pin1724to be moved radially inward to a retracted or release position. Once the retainer pin1724is in the release position, the socket wrench can he removed from the square socket drive1718a.When cam ring1724moves to its forward axial position in the first mode of operation (FIG. 18A), the spring1726causes the actuator pin1748to move upward, causing the lever pin1730to rotate in a clockwise direction CW so that the retainer pin1724extends in an engaged position.

The first and second electromagnetic coils1766,1770can be electrically connected to the tool battery or an alternative power source such as an A/C power source by a control circuit, such as one of the control circuits described above. A user-actuatable switch for controlling movement of the cam ring1740by the electromagnets can be placed at one or more of multiple different locations on the power tool1710, as indicated by the X's inFIG. 17. Thus, the socket release mechanism can be controlled from virtually any location on the tool. It should be understood that this type of electromechanical socket release mechanism can be used with any of the other disclosed embodiments for a socket release mechanism described in U.S. patent application Ser. No. 13/494,325.

Numerous other modifications may be made to the exemplary implementations described above. For example, any of the above-described combinations of permanent magnet and electromagnetic assemblies may he exchanged from any of the other combinations. The above-described electromagnetic assemblies for moving actuators can be used for any other applications or designs of power tools that require movement of actuators among two or more positions. These and other implementations are within the scope of the following claims.