ELECTROSTATIC CLUTCH FOR POWER TOOL

A power tool that includes a housing, a motor, an end effector, an electrostatic clutch assembly, and a control circuit is provided. In a first mode of operation, the control circuit causes a first voltage to be applied to a first electrode and a different second voltage to be applied to a second electrode, generating a first attractive force between the first and second electrodes, which causes an output member to rotate together with an input member when a torque on the output member is less than or equal to a first threshold value and which causes the output member to rotationally slip relative to the input member when the torque on the output member exceeds the first threshold value, interrupting torque transmission from the input member to the output member.

FIELD

The present patent application relates to power tools and electrostatic clutches/mechanisms for power tools.

BACKGROUND

Many power tools, such as power drills, power drivers, power fastening tools and/or other power tools, have a mechanical clutch that interrupts power transmission to the output spindle/shaft when the output torque exceeds a threshold value of a maximum torque. U.S. Pat. No. 9,494,200, which is incorporated by reference in the patent application in its entirety, provides an exemplary prior art mechanical clutch. Such a mechanical clutch is a purely mechanical device that breaks a mechanical connection in the transmission to prevent torque from being transmitted from the motor to the output spindle/shaft of the power tool. Clutches or slip clutches are generally used in the power tools to provide torque limited application at the working bit. Traditional slip clutches have been executed mechanically with balls, springs, and clutch plates. In these mechanical clutches, the maximum torque threshold value may be user adjustable, often by a clutch collar that is attached to the power tool between the power tool and the tool holder/chuck. The user may rotate the clutch collar among a plurality of different positions for different maximum torque settings. The components of the mechanical clutches, however, tend to wear over time, and add excessive bulk and weight to a power tool.

In order to save length and cost, some power tools additionally or alternatively include an electronic clutch. Such an electronic clutch electronically senses the output torque (e.g., via a torque transducer) or infers the output torque (e.g., by sensing another parameter such as current drawn by the motor). U.S. Pat. No. 10,220,500, which is incorporated by reference in the present patent application its entirety, provides an exemplary prior art electronic clutch. When the electronic clutch determines that the sensed output torque exceeds a threshold value, it interrupts or reduces power transmission to the output shaft/spindle, either mechanically (e.g., by actuating a solenoid to break a mechanical connection in the transmission) or electrically (e.g., by interrupting or reducing current delivered to the motor, and/or by actively braking the motor). Existing electronic clutches tend to be overly complex and/or inaccurate. For example, electronic clutches suffer in performance in that they sense current at the motor module to estimate the applied torque at the working bit. The intermediary elements (i.e., the motor & transmission) result in latency in applying torque limiting and also introduce inaccuracies.

Other type of clutches, such as electromagnetic clutches feature fast activation and moderate torque density, but require continuous electrical power to stay active. Magnetorheological clutches produce large torques, but are heavy and also require continuous power to remain active. Because of the power requirements, both of these systems require large batteries or tethered electrical connections. Batteries in particular account for a significant portion of the weight of many devices, such as power tools, especially in devices with clutches that require constant power.

FIG.1shows an exemplary prior art saw braking mechanism150. The saw braking mechanism150works by sensing that the saw blade152is in contact with flesh of the user which then activates a compressed gas cartridge156to force a blade stopping element154into the saw blade152to quickly arrest motion of the saw blade152. For example, U.S. Pat. No. 8,011,279, which is incorporated by reference in the present patent application in its entirety provides an exemplary prior art saw braking mechanism. The saw braking mechanism150, when activated, is not recoverable and must be replaced. The saw braking mechanism150is also expensive, time consuming to replace, and results in work stoppage/lost productivity.

SUMMARY

The present patent application provides improvements in the clutches for power tools.

One aspect of the present patent application provides a power tool. The power tool includes a housing, a motor, an end effector, an electrostatic clutch assembly, and a control circuit. The housing is configured to be coupled to an electrical power source. The motor is received in the housing. The end effector is coupled to the housing and is configured to perform an operation on a workpiece. The electrostatic clutch assembly is disposed in the housing between the motor and the end effector. The electrostatic clutch assembly includes an input member configured to be rotationally driven by the motor, an output member configured to rotationally drive the end effector, a first electrode electrically couplable to the electrical power source, a second electrode electrically couplable to the electrical power source, and a dielectric layer separating the first electrode from the second electrode. The control circuit is disposed in the housing and is operatively cooperable with the electrostatic clutch assembly to control electrical power delivery from the electrical power source to the first and second electrodes. In a first mode of operation, the control circuit causes a first voltage to be applied to the first electrode and a different second voltage to be applied to the second electrode, generating a first attractive force between the first and second electrodes, which causes the output member to rotate together with the input member when a torque on the output member is less than or equal to a first threshold value and which causes the output member to rotationally slip or rotate relative to the input member when the torque on the output member exceeds the first threshold value, interrupting torque transmission from the input member to the output member.

In one embodiment, the first threshold corresponds to the first attractive force. In one embodiment, in a second mode of operation, the control circuit causes a third voltage to be applied to the first electrode and a different fourth voltage to be applied to the second electrode, generating a second attractive force between the first and second electrodes, which causes the output member to rotate together with the input member when a torque on the output member is less than or equal to a second threshold value and which causes the output member to rotationally slip or rotate relative to the input member when the torque on the output member exceeds the second threshold value, interrupting torque transmission from the input member to the output member. In one embodiment, a second voltage difference between the third voltage and the fourth voltage is greater than a first voltage difference between the first voltage and the second voltage, the second attractive force is greater than the first attractive force, and the second threshold value is greater than the first threshold value. In one embodiment, the power tool further comprises a selector switch coupled to the housing that is actuatable by a user to select between the first and second modes of operation. In one embodiment, in a third mode of operation, the control circuit causes a zero voltage difference to be applied to the first and second electrodes, allowing the second electrode to rotate relative to the first electrode and preventing torque transmission from the input member to the output member. In one embodiment, the control circuit is configured to automatically switch from the first mode to the third mode upon sensing that the output member has rotationally slipped or rotated relative to the input member. In one embodiment, in a fourth mode of operation, the clutch assembly is configured to prevent interruption of torque transmission from the input member to the output member.

In the fourth mode of operation, the control circuit may cause a fifth voltage to be applied to the first electrode and a different sixth voltage to be applied to the second electrode, generating a third attractive force between the first and second electrodes, the third attractive force exceeding a torque on the output member during operation of the power tool. The second voltage may have a polarity opposite a polarity of the first voltage. The first voltage difference may be user selectable to adjust the first attractive force and the first threshold value. A greater voltage difference may correspond to a greater first attractive force and a greater first threshold value.

Each of the first electrode and the second electrode may include an annular plate member. One of the first electrode and the second electrode may include a cylindrical member and the other of the first electrode and the second electrode includes a different diameter coaxial cylindrical member received within the cylindrical member. Each of the first electrode and the second electrode may include a frictional surface disposed on at least a portion thereof. The electrostatic clutch assembly may include a plurality of clutch settings, each clutch setting corresponds to a desired output operation of the power tool, and each clutch setting has the set torque. Each of the first electrode and the second electrode may include conductive material disposed on at least a portion thereof.

The conductive material may be disposed on surfaces of the first electrode and the second electrode that face each other. Each of the first electrode and the second electrode may include at least one conductive material layer. The at least one conductive material layer may be disposed on surfaces of the first electrode and the second electrode that face each other. The electrostatic clutch assembly may include positive and negative brushes that are stationary relative to the housing and are configured provide the electrical field to the first electrode and the second electrode.

The output shaft may be configured to drive a tool holder that is configured to receive a tool bit portion therein. The output shaft may have a first end portion and an opposing second end portion. One of the first end portion and the opposing second end portion may be operatively connected to the second electrode, and the other of the first end portion and the opposing second end portion may be operatively connected to the tool holder.

The first electrode may be operatively connected to the motor via an input shaft that is driven by a motor and transmission assembly. Each of the first electrode and the second electrode may include an annular member, a thrust bearing, and an electrostatic film member. The thrust bearing of each of the first electrode and the second electrode may be operatively connected to the associated annular member and the associated electrostatic film member. The annular members of the first electrode and the second electrode may be operatively connected to the motor and the output shaft, respectively.

Yet another aspect of the present patent application provides a power tool. The power tool comprises a housing, an output shaft, a motor, an electrostatic clutch assembly, and a controller. The electrostatic clutch assembly is disposed in the housing and includes a first electrode operatively connected to the motor and a second electrode operatively connected to the output shaft. The motor is disposed in the housing and is configured to provide a torque to the output shaft. The controller is disposed in the housing and is operatively cooperable with the electrostatic clutch assembly to operate in a fully disengaged mode wherein an electric field below a second predetermined threshold between the first electrode and the second electrode causes the output shaft to be rotationally decoupled from the motor, and in a clutch mode wherein an electric field between the first predetermined threshold and the second predetermined threshold is applied across the first electrode and the second electrode causing a second electrostatic force between the first electrode and the second electrode to rotationally couple the output shaft with the motor such that the output shaft moves together at the same velocity when the torque therebetween is below a set torque and to permit the motor to rotate at a higher velocity than the output shaft when the torque therebetween is above the set torque.

The controller may be disposed in the housing and is operatively cooperable with the electrostatic clutch assembly to operate in a fully engaged mode wherein an electric field above a first predetermined threshold is applied across the first electrode and the second electrode causing a first electrostatic force between the first electrode and the second electrode to rotationally couple the output shaft with the motor such that the output shaft and the motor move together at the same velocity. In one embodiment, when the electrostatic clutch assembly is in the fully disengaged mode, there is no electrostatic charge present between the first electrode and the second electrode of the electrostatic clutch assembly. In one embodiment, when the electrostatic clutch assembly is in the fully disengaged mode, the first electrode and the second electrode of the electrostatic clutch assembly are not attracted to each other. In one embodiment, when the electrostatic clutch assembly is in the fully disengaged mode, the first electrode and the second electrode of the electrostatic clutch assembly are positioned in such a way that a gap exists between surfaces of the first electrode and the second electrode that face each other. In one embodiment, when the electrostatic clutch assembly is in the clutch mode and when the torque between the output shaft and the motor is above the set torque, the velocity of the output shaft is zero. In one embodiment, when the electrostatic clutch assembly is in the fully engaged mode, the first electrode and the second electrode of the electrostatic clutch assembly are attracted to each other. In one embodiment, when the electrostatic clutch assembly is in the fully engaged mode, the first electrode and the second electrode of the electrostatic clutch assembly are positioned in such a way that no gap exists between surfaces of the first electrode and the second electrode that face each other. In one embodiment, when the electrostatic clutch assembly is in the clutch mode, the first electrode and the second electrode of the electrostatic clutch assembly are variably attracted to each other. In one embodiment, when the electrostatic clutch assembly is in the clutch mode, the first electrode and the second electrode of the electrostatic clutch assembly are positioned in such a way that no gap exists between surfaces of the first electrode and the second electrode that face each other. In one embodiment, the power tool further comprises a sensor configured to sense whether the electrostatic clutch assembly is in the fully engaged mode, the fully disengaged mode, or the clutch mode and output a signal to the controller. In one embodiment, the controller, in response to the received signal from the sensor, is configured to stop the rotation of the motor. The sensor may comprise one or more of a current sensor, a position sensor, and a rotational motion sensor. In one embodiment, each of the first electrode and the second electrode includes an annular plate member. In one embodiment, one of the first electrode and the second electrode includes a cylindrical member and the other of the first electrode and the second electrode includes a different diameter coaxial cylindrical member received within the cylindrical member.

In one embodiment, each of the first electrode and the second electrode includes a brake pad disposed on at least a portion thereof. In one embodiment, the electrostatic clutch assembly includes a plurality of clutch settings, each clutch setting corresponds to a desired output operation of the power tool, and each clutch setting has the set torque. In one embodiment, each of the first electrode and the second electrode includes conductive material disposed on at least a portion thereof. In one embodiment, the conductive material is disposed on surfaces of the first electrode and the second electrode that face each other. In one embodiment, each of the first electrode and the second electrode includes at least one conductive material layer. In one embodiment, the at least one conductive material layer is disposed on surfaces of the first electrode and the second electrode that face each other. In one embodiment, the electrostatic clutch assembly includes positive and negative brushes that are stationary relative to the housing and are configured provide the electrical field to the first electrode and the second electrode when the electrostatic clutch assembly is in either the fully engaged mode or the clutch mode. In one embodiment, the output shaft is configured to drive a tool holder that is configured to receive a tool bit portion therein. In one embodiment, the output shaft has a first end portion and an opposing second end portion. In one embodiment, one of the first end portion and the opposing second end portion is operatively connected to the second electrode, and the other of the first end portion and the opposing second end portion is operatively connected to the tool holder. In one embodiment, the first electrode is operatively connected to the motor via an input shaft that is driven by a motor and transmission assembly. In one embodiment, each of the first electrode and the second electrode includes an annular member, a thrust bearing, and an electrostatic film member. In one embodiment, the thrust bearing of each of the first electrode and the second electrode is operatively connected to the associated annular member and the associated electrostatic film member. In one embodiment, the annular members of the first electrode and the second electrode are operatively connected to the motor and the output shaft, respectively.

Yet another aspect of the present patent application provides an electrostatic clutch assembly for a power tool. The electrostatic clutch assembly may comprise an input member configured to be selectively driven in motion; an output member configured to selectively output a motion; a first electrode electrically couplable to an electrical power source; a second electrode electrically couplable to the electrical power source; a dielectric layer separating the first electrode from the second electrode; and a control circuit operatively cooperable with the first electrode from the second electrode to control electrical power delivery from the electrical power source to the first and second electrodes. In one embodiment, in a first mode of operation, the control circuit may cause a first voltage to be applied to the first electrode and a different second voltage to be applied to the second electrode, generating a first attractive force between the first and second electrodes, which causes the output member to rotate together with the input member when a torque on the output member is less than or equal to a first threshold value and which causes the output member to rotationally slip relative to the input member when the torque on the output member exceeds the first threshold value, interrupting torque transmission from the input member to the output member.

In one embodiment, the first threshold may correspond to the first attractive force. In one embodiment, in a second mode of operation, the control circuit may cause a third voltage to be applied to the first electrode and a different fourth voltage to be applied to the second electrode, generating a second attractive force between the first and second electrodes, which causes the output member to rotate together with the input member when a torque on the output member is less than or equal to a second threshold value and which causes the output member to rotationally slip relative to the input member when the torque on the output member exceeds the second threshold value, interrupting torque transmission from the input member to the output member.

In one embodiment, a second voltage difference between the third voltage and the fourth voltage is greater than a first voltage difference between the first voltage and the second voltage, the second attractive force may be greater than the first attractive force, and the second threshold value may be greater than the first threshold value. In one embodiment, the electrostatic clutch assembly may further comprise a selector switch actuatable by a user to select between the first and second modes of operation. In one embodiment, in a third mode of operation, the control circuit may cause a zero voltage difference to be applied to the first and second electrodes, allowing the second electrode to rotate relative to the first electrode and preventing torque transmission from the input member to the output member. In one embodiment, the control circuit may be configured to automatically switch from the first mode to the third mode upon sensing that the output member has rotationally slipped relative to the input member. In one embodiment, in a fourth mode of operation, the clutch assembly may be configured to prevent interruption of torque transmission from the input member to the output member.

In the fourth mode of operation, the control circuit may cause a fifth voltage to be applied to the first electrode and a different sixth voltage to be applied to the second electrode, generating a third attractive force between the first and second electrodes, the third attractive force exceeding a torque on the output member during operation of the power tool. The second voltage may have a polarity opposite a polarity of the first voltage. The first voltage difference may be user selectable to adjust the first attractive force and the first threshold value, and a greater voltage difference corresponds to a greater first attractive force and a greater first threshold value.

Each of the first electrode and the second electrode may include an annular plate member. One of the first electrode and the second electrode may include a cylindrical member and the other of the first electrode and the second electrode includes a different diameter coaxial cylindrical member received within the cylindrical member. Each of the first electrode and the second electrode may include a frictional surface disposed on at least a portion thereof.

The electrostatic clutch assembly may include a plurality of clutch settings, each clutch setting may correspond to a desired output operation of the power tool, and each clutch setting has the set torque. Each of the first electrode and the second electrode may include conductive material disposed on at least a portion thereof. The conductive material may be disposed on surfaces of the first electrode and the second electrode that face each other. Each of the first electrode and the second electrode may include at least one conductive material layer. The at least one conductive material layer may be disposed on surfaces of the first electrode and the second electrode that face each other. The electrostatic clutch assembly may include positive and negative brushes that are stationary relative to the housing and are configured provide the electrical field to the first electrode and the second electrode. The output member may be configured to drive a tool holder of the power tool that is configured to receive a tool bit portion therein. The output member may be a first end portion and an opposing second end portion. One of the first end portion and the opposing second end portion may be operatively connected to the second electrode. The other of the first end portion and the opposing second end portion may be operatively connected to the tool holder.

The first electrode may be operatively connected to a motor of the power tool via the input member that is driven by a motor and transmission assembly of the power tool. Each of the first electrode and the second electrode may include an annular member, a thrust bearing, and an electrostatic film member. The thrust bearing of each of the first electrode and the second electrode may be operatively connected to the associated annular member and the associated electrostatic film member. The annular members of the first electrode and the second electrode may be operatively connected to a motor of the power tool and the output member, respectively.

Yet another aspect of the present patent application provides an electrostatic clutch assembly for a power tool. The electrostatic clutch may comprise an input member configured to be selectively driven in motion; an output member configured to selectively output a motion; a first electrode electrically couplable to an electrical power source; a second electrode electrically couplable to an electrical power source; and a controller. The controller may be configured to operate: in a fully disengaged mode wherein an electric field below a second predetermined threshold between the first electrode and the second electrode causes the output member to be rotationally decoupled from the input member, and in a clutch mode wherein an electric field between the first predetermined threshold and the second predetermined threshold is applied across the first electrode and the second electrode causing a second electrostatic force between the first electrode and the second electrode to rotationally couple the output member with the input member such that the output member moves together at the same velocity when the torque therebetween is below a set torque and to permit the input member to rotate at a higher velocity than the output member when the torque therebetween is above the set torque.

In one embodiment, the controller may be configured to operate in a fully engaged mode wherein an electric field above a first predetermined threshold is applied across the first electrode and the second electrode causing a first electrostatic force between the first electrode and the second electrode to rotationally couple the output member with the input member such that the output member and the input member move together at the same velocity.

In one embodiment, when the electrostatic clutch assembly is in the fully disengaged mode, there may be no electrostatic charge present between the first electrode and the second electrode of the electrostatic clutch assembly. In one embodiment, when the electrostatic clutch assembly is in the fully disengaged mode, the first electrode and the second electrode of the electrostatic clutch assembly may not be attracted to each other. When the electrostatic clutch assembly is in the fully disengaged mode, the first electrode and the second electrode of the electrostatic clutch assembly may be positioned in such a way that a gap exists between surfaces of the first electrode and the second electrode that face each other. In one embodiment, when the electrostatic clutch assembly is in the clutch mode and when the torque between the output member and the input member is above the set torque, the velocity of the output member may be zero.

In one embodiment, when the electrostatic clutch assembly is in the fully engaged mode, the first electrode and the second electrode of the electrostatic clutch assembly may be attracted to each other. When the electrostatic clutch assembly is in the fully engaged mode, the first electrode and the second electrode of the electrostatic clutch assembly may be positioned in such a way that no gap exists between surfaces of the first electrode and the second electrode that face each other.

In one embodiment, when the electrostatic clutch assembly is in the clutch mode, the first electrode and the second electrode of the electrostatic clutch assembly are variably attracted to each other. In one embodiment, when the electrostatic clutch assembly is in the clutch mode, the first electrode and the second electrode of the electrostatic clutch assembly may be positioned in such a way that no gap exists between surfaces of the first electrode and the second electrode that face each other. In one embodiment, the electrostatic clutch assembly may further comprise a sensor configured to sense whether the electrostatic clutch assembly is in the fully engaged mode, the fully disengaged mode, or the clutch mode and output a signal to the controller. The controller, in response to the received signal from the sensor, may be configured to stop the rotation of a motor. The sensor may comprise one or more of a current sensor, a position sensor, and a rotational motion sensor.

In one embodiment, each of the first electrode and the second electrode may include an annular plate member. In one embodiment, one of the first electrode and the second electrode may include a cylindrical member and the other of the first electrode and the second electrode may include a different diameter coaxial cylindrical member received within the cylindrical member. In one embodiment, each of the first electrode and the second electrode may include a brake pad disposed on at least a portion thereof. In one embodiment, the electrostatic clutch assembly may include a plurality of clutch settings, each clutch setting corresponds to a desired output operation of a power tool, and each clutch setting has the set torque.

In one embodiment, each of the first electrode and the second electrode may include conductive material disposed on at least a portion thereof. In one embodiment, the conductive material may be disposed on surfaces of the first electrode and the second electrode that face each other.

In one embodiment, each of the first electrode and the second electrode may include at least one conductive material layer. In one embodiment, the at least one conductive material layer may be disposed on surfaces of the first electrode and the second electrode that face each other. In one embodiment, the electrostatic clutch assembly may include positive and negative brushes that are stationary relative to the housing and are configured provide the electrical field to the first electrode and the second electrode when the electrostatic clutch assembly is in either the fully engaged mode or the clutch mode.

In one embodiment, the output member may be configured to drive a tool holder of the power tool that is configured to receive a tool bit portion therein. The output member may have a first end portion and an opposing second end portion. The one of the first end portion and the opposing second end portion may be operatively connected to the second electrode. The other of the first end portion and the opposing second end portion may be operatively connected to the tool holder.

In one embodiment, the first electrode may be operatively connected to a motor of the power tool via the input member that is driven by a motor and transmission assembly of the power tool. In one embodiment, each of the first electrode and the second electrode may include an annular member, a thrust bearing, and an electrostatic film member. The thrust bearing of each of the first electrode and the second electrode may be operatively connected to the associated annular member and the associated electrostatic film member. The annular members of the first electrode and the second electrode may be operatively connected to the input member and the output member, respectively.

Yet another aspect of the present patent application provides a power tool. The power tool may comprise a housing configured to be coupled to an electrical power source; a motor received in the housing; an end effector coupled to the housing and configured to perform an operation on a workpiece; an electrostatic clutch assembly disposed in the housing between the motor and the end effector. The electrostatic clutch assembly may include an input member configured to be selectively driven by the motor; an output member configured to selectively output to the end effector; at least one frictional surface; a first electrode electrically couplable to the electrical power source; a second electrode electrically couplable to the electrical power source; and a dielectric layer separating the first electrode from the second electrode. The power tool may further comprise a control circuit operatively cooperable with the first and second electrodes to control electrical power delivery from the electrical power source to the first and second electrodes. In one embodiment, in a first mode of operation, the control circuit may cause a first voltage to be applied across the first electrode and a different second to be applied to the second electrode, generating a first attractive force between the first and second electrodes, which causes the frictional surface to frictionally engage with at least one of the input member and the output member to enable motion to be transmitted from the input member to the output member.

In one embodiment, in the first mode of operation, motion from the input member to the output member may be interrupted when a force applied to the output member is greater than a first threshold value. In one embodiment, the first threshold value may correspond to a frictional force between the frictional surface and at least one of the input member and the output member. In one embodiment, in a second mode of operation, the control circuit may cause a third voltage to be applied to the first electrode and a different fourth voltage to be applied to the second electrode, generating a second attractive force between the first and second electrodes, which causes the frictional surface to frictionally engage with at least one of the input member and the output member to enable motion to be transmitted from the input member to the output member when a force applied to the output member is less than or equal to a second threshold value and to interrupt force transmission from the input member to the output member when the force applied to the output member is greater than the second threshold value.

In one embodiment, the third voltage may be greater than the first voltage, the fourth voltage may be greater than the second voltage, the second attractive force may be greater than the first attractive force, and the second threshold value may be greater than the first threshold value. In one embodiment, the power tool may further comprise a selector switch coupled to the housing that is actuatable by a user to select between the first and second modes of operation. In one embodiment, in a third mode of operation, the control circuit may cause zero voltage to be applied to the first and second electrodes, preventing motion from being transmitted from the input member to the output member. In one embodiment, the control circuit may be configured to automatically switch from the first mode to the third mode upon sensing that the motion transmission from the input member to the output member has been interrupted.

Each of the first electrode and the second electrode may include an annular plate member. One of the first electrode and the second electrode may include a cylindrical member and the other of the first electrode and the second electrode includes a different diameter coaxial cylindrical member received within the cylindrical member.

Each of the first electrode and the second electrode may include a frictional surface disposed on at least a portion thereof. The electrostatic clutch assembly may include a plurality of clutch settings, each clutch setting may correspond to a desired output operation of the power tool, and each clutch setting has the set torque. Each of the first electrode and the second electrode may include conductive material disposed on at least a portion thereof. The conductive material may be disposed on surfaces of the first electrode and the second electrode that face each other.

Each of the first electrode and the second electrode may include at least one conductive material layer. The at least one conductive material layer may be disposed on surfaces of the first electrode and the second electrode that face each other. The electrostatic clutch assembly may include positive and negative brushes that are stationary relative to the housing and are configured provide the electrical field to the first electrode and the second electrode.

The output shaft may be configured to drive a tool holder of the power tool that is configured to receive a tool bit portion therein. The output shaft may have a first end portion and an opposing second end portion. One of the first end portion and the opposing second end portion may be operatively connected to the second electrode. The other of the first end portion and the opposing second end portion may be operatively connected to the tool holder.

The first electrode may be operatively connected to the motor of the power tool via an input shaft that is driven by a motor and transmission assembly of the power tool. Each of the first electrode and the second electrode may include an annular member, a thrust bearing, and an electrostatic film member. The thrust bearing of each of the first electrode and the second electrode may be operatively connected to the associated annular member and the associated electrostatic film member. The annular members of the first electrode and the second electrode may be operatively connected to the motor and the output shaft, respectively.

Another aspect of the present patent application provides an electrostatic clutch assembly for a power tool. The electrostatic clutch assembly includes an input member, an output member, at least one frictional surface, a first electrode, a second electrode, a dielectric layer, and a control circuit. The input member is configured to be selectively driven in motion. The output member is configured to selectively output a motion. The first electrode is electrically couplable to the electrical power source. The second electrode is electrically couplable to the electrical power source. The dielectric layer is separating the first electrode from the second electrode. The control circuit is operatively cooperable with the first and second electrodes to control electrical power delivery from the electrical power source to the first and second electrodes. In a first mode of operation, the control circuit causes a first voltage to be applied to the first electrode and a different second voltage to be applied to the second electrode, generating a first attractive force between the first and second electrodes, which causes the frictional surface to frictionally engage with at least one of the input member and the output member to enable motion to be transmitted from the input member to the output member.

In one embodiment, in the first mode of operation, motion from the input member to the output member is interrupted when a force applied to the output member is greater than a first threshold value. In one embodiment, the first threshold value corresponds to a frictional force between the frictional surface and at least one of the input member and the output member. In one embodiment, in a second mode of operation, the control circuit causes a third voltage to be applied to the first electrode and a different fourth voltage to be applied to the second electrode, generating a second attractive force between the first and second electrodes, which causes the frictional surface to frictionally engage with at least one of the input member and the output member to enable motion to be transmitted from the input member to the output member when a force applied to the output member is less than or equal to a second threshold value and the to interrupt force transmission from the input member to the output member when the force applied to the output member is greater than the second threshold value. In one embodiment, the third voltage is greater than the first voltage, the fourth voltage is greater than the second voltage, the second attractive force is greater than the first attractive force, and the second threshold value is greater than the first threshold value. In one embodiment, the power tool further comprises a selector switch actuatable by a user to select between the first and second modes of operation. In one embodiment, in a third mode of operation, the control circuit causes zero voltage to be applied to the first and second electrodes, preventing motion from being transmitted from the input member to the output member. In one embodiment, the control circuit is configured to automatically switch from the first mode to the third mode upon sensing that the motion transmission from the input member to the output member has been interrupted.

Each of the first electrode and the second electrode may include an annular plate member. One of the first electrode and the second electrode may include a cylindrical member and the other of the first electrode and the second electrode includes a different diameter coaxial cylindrical member received within the cylindrical member. Each of the first electrode and the second electrode may include a frictional surface disposed on at least a portion thereof.

The electrostatic clutch assembly may include a plurality of clutch settings, each clutch setting may correspond to a desired output operation of the power tool, and each clutch setting has the set torque. Each of the first electrode and the second electrode may include conductive material disposed on at least a portion thereof. The conductive material may be disposed on surfaces of the first electrode and the second electrode that face each other. Each of the first electrode and the second electrode may include at least one conductive material layer. The at least one conductive material layer may be disposed on surfaces of the first electrode and the second electrode that face each other.

The electrostatic clutch assembly may include positive and negative brushes that are stationary relative to the housing and are configured provide the electrical field to the first electrode and the second electrode.

The output shaft may be configured to drive a tool holder of the power tool that is configured to receive a tool bit portion therein. The output shaft may have a first end portion and an opposing second end portion. One of the first end portion and the opposing second end portion may be operatively connected to the second electrode, and wherein the other of the first end portion and the opposing second end portion is operatively connected to the tool holder. The first electrode may be operatively connected to the motor of the power tool via an input shaft that is driven by a motor and transmission assembly of the power tool.

Each of the first electrode and the second electrode may include an annular member, a thrust bearing, and an electrostatic film member. The thrust bearing of each of the first electrode and the second electrode may be operatively connected to the associated annular member and the associated electrostatic film member. The annular members of the first electrode and the second electrode may be operatively connected to the motor and the output shaft, respectively.

DETAILED DESCRIPTION

In one embodiment, the present patent application provides electrostatic clutches or electro-mechanical electrostatic clutches for power tools. In one embodiment, the present patent application provides electroadhesive clutches or electro-mechanical electroadhesive clutches for power tools. In one embodiment, the present patent application provides electrostatic clutches, electro-mechanical electrostatic clutches, electroadhesive clutches, or electro-mechanical electroadhesive clutches for other power devices.

In one embodiment, referring toFIGS.2-5and13, the present patent application provides a power tool10. The power tool10includes a housing12, a motor and transmission assembly14, an end effector22, an electrostatic clutch assembly18, and a control circuit50. The housing12is configured to be coupled to an electrical power source102. The motor and transmission assembly14is received in the housing12. The end effector22is coupled to the housing12and is configured to perform an operation on a workpiece (not shown). The electrostatic clutch assembly18is disposed in the housing12between the motor and transmission assembly14and the end effector22. The electrostatic clutch assembly18includes an input member66configured to be rotationally driven by the motor and transmission assembly14, an output member68configured to rotationally drive the end effector22, a first electrode42electrically couplable to the electrical power source102, a second electrode44electrically couplable to the electrical power source102, and a dielectric layer106separating the first electrode42and the second electrode44. In one embodiment, the motor and transmission assembly14may include a motor15and a transmission16. In another embodiment, the motor and transmission assembly14may include the motor15.

In one embodiment, as shown and described in detail below with respect to the embodiments ofFIGS.2-6, the present patent application provides the electrostatic clutch assembly18for the power tool10that is configured to slip or rotate at a torque level while the charge is still applied to the electrostatic film/layers60of the first and second electrodes42,44, especially where there are multiple clutch settings that correspond to different torque levels and charge amounts. In one embodiment, as shown and described in detail below with respect to the embodiments ofFIGS.7-9B and12A-C, the power tool system200or400also uses frictional elements/brake pad(s)262/462along with the electrostatic film/layers260/460of the first and second electrodes242,244or442,444as part of the electrostatic clutch assembly218/418. In one embodiment, as shown and described with respect to the embodiments ofFIGS.10-11, the power tool system300also may use thrust bearing(s)364along with the electrostatic film/layers360of the first and second electrodes342,344as part of the electrostatic clutch assembly318. In one embodiment, as shown and described in detail with respect to the embodiments ofFIGS.14-17, the present patent application further uses this electrostatic technology/mechanism to quickly stop/brake a spinning object upon a detected event.

In the first embodiment ofFIGS.2-5and13, the control circuit50is disposed in the housing12and is operatively cooperable with the motor and transmission assembly14and the electrostatic clutch assembly18to control electrical power delivery from the electrical power source102to the motor and transmission assembly14and to the first and second electrodes42,44. In a first mode of operation, the control circuit50causes a voltage difference to be applied across the first and second electrodes42,44, generating a first attractive force between the first and second electrodes42,44. For example, a first voltage may be applied to the first electrode42and a second voltage with a polarity opposite a polarity the first voltage may be applied to the second electrode44, generating a first attractive force between the first and second electrodes42,44. That is, in the first mode of operation, the control circuit50may cause the first voltage to be applied to the first electrode42and a different second voltage to be applied to the second electrode44. This causes the output member68to rotate together with the input member66when a torque on the output member68is less than or equal to a first threshold value and which allows the output member68to rotationally slip or rotate relative to the input member66when the torque on the output member68exceeds the first threshold value, interrupting torque transmission from the input member66to the output member68.

In one embodiment, the electrostatic clutch18ofFIGS.2-6and13(and also electrostatic clutch218inFIGS.7-9B, electrostatic clutch318inFIGS.10-11, electrostatic clutch418inFIGS.12A-12C, and electrostatic clutch518inFIGS.14-17) of the present patent application may employ the clutches disclosed in U.S. Pat. Nos. 10,355,624; 10,554,154; and 10,749,450. and U.S. Patent Application Publication No. 2020/0177109, each of which is incorporated by reference in their entirety herein. In one embodiment, the electrostatic clutches18,218,318,418, or518of the present patent application employ the clutches described in Stuart B Diller, Steven H Collins, and Carmel Majidi. (2018). The effects of electroadhesive clutch design parameters on performance characteristics.Journal of Intelligent Material Systems and Structures, Vol. 29(19), 3804-3828, which is incorporated by reference in its entirety.

FIG.2illustrates two superimposed versions of the electrostatic clutch assembly18. For ease of understanding and sake of clarity, these two embodiments of the electrostatic clutch assembly18inFIG.2are shown separately inFIGS.2A and2B. Other than these differences noted below, the operation and the configuration of the electrostatic clutch assembly18inFIG.2are same as those of the electrostatic clutch assemblies18inFIGS.2A and2B. Specifically,FIG.2Ashows operational connections between the control circuit50, the electrical power source102and the first and second electrodes42,44in accordance with an embodiment of the present patent application.FIG.2Bshows different operational connections between the control circuit50, the electrical power source102and the first and second electrodes42,44in accordance with another embodiment of the present patent application.

These operational connections ofFIGS.2A and2Bmay be configured to enable the control circuit50, disposed in the housing12and operatively cooperable with the electrostatic clutch assembly18, to control electrical power delivery from the electrical power source102to the first and second electrodes42,44, which in turn enables one of the first and second electrodes42,44to be a positively charged electrode and the other of the first and second electrodes42,44to be a negatively charged electrode. One of the first and second electrodes42,44may be positively charged when a first voltage is applied to one of the first and second electrodes42,44and the other of the first and second electrodes42,44may be negatively charged when a second voltage with a polarity opposite a polarity the first voltage may be applied to the other of the first and second electrodes42,44. In one embodiment, the first and second electrodes42,44of the electrostatic clutch assembly18comprise a parallel-plate capacitor (i.e., two conducting plates42,44, with a dielectric therebetween). The plates are oppositely charged, as with any capacitor.

LikeFIG.2, each ofFIGS.7,10,11and12Cpresents, for sake of brevity, a superimposed figure with two embodiments of the electrostatic clutch assembly. Each of these two embodiments inFIGS.7,10,11and12Chas different operational connections between the control circuit, the electrical power source and the first and second electrodes. A person of ordinary skill in the art would readily appreciate that each of these two embodiments inFIGS.7,10,11and12Cmay be presented separately or individually, for example, as shown inFIGS.2A and2B.

In one embodiment, the output member68may be interchangeably referred to as output shaft68. In one embodiment, the control circuit50may be interchangeably referred to as controller50. In one embodiment, the end effector22may be interchangeably referred to as chuck or tool holder22.

In one embodiment, the controller50is operatively cooperable with the motor and transmission assembly14and the electrostatic clutch assembly18to operate: (1) in a fully engaged mode wherein an electric field above a first predetermined threshold is applied across the first electrode42and the second electrode44causing a first electrostatic force between the first electrode42and the second electrode44to rotationally couple the output member68with the input member66and the motor and transmission assembly14such that the output shaft68and the motor and transmission assembly14/input member66rotate together at the same velocity; (2) in a fully disengaged mode wherein an electric field below a second predetermined threshold between the first electrode42and the second electrode44causes the output member68to be rotationally decoupled from the input member66/motor and transmission assembly14, and/or (3) in a clutch mode wherein an electric field between the first predetermined threshold and the second predetermined threshold is applied across the first electrode42and the second electrode44causing a second electrostatic force between the first electrode42and the second electrode44to rotationally couple the output member68with the motor and transmission assembly14/input member66such that the output member68rotates together at the same velocity when the torque therebetween is below a set torque and to decouple the output member68from the input member66so that the output member68can rotate at a lower or zero velocity while the motor and transmission assembly14continues to rotate at a higher velocity when the torque therebetween is above the set torque.

FIG.13shows an exemplary power tool10constructed in accordance with the teachings of the present patent application. As those skilled in the art will appreciate, embodiments may include either a corded or cordless (battery operated) power tool/device. In one embodiment, the power tool is a power screwdriver, a power fastener/fastening tool, a power driver, a power drill, a power expansion tool, and/or other power tools. In illustrated embodiment ofFIG.13, the power tool10is a power (cordless) drill/screwdriver. In one embodiment, the power tool10is a portable device.

In one embodiment, the power tool10generally includes the housing12, the motor and transmission assembly14(which includes the motor15and a transmission16, such as a multi-speed transmission assembly16), the electrostatic clutch/electrostatic clutch assembly18, the output shaft/output spindle assembly68, the tool holder/chuck22, a trigger assembly24and a battery pack26. Those skilled in the art will understand that several of the components of the power tool10, such as the tool holder22, the trigger assembly24and the battery pack26, are conventional in nature and therefore need not be discussed in significant detail in the present patent application. Reference may be made to a variety of patents/patent publications for a more complete understanding of the conventional features of the power tool10. One example of such patents is U.S. Pat. No. 5,897,454 issued Apr. 27, 1999, which is hereby incorporated by reference in the present patent application in its entirety.

Referring toFIG.13, the housing12includes a pair of mating handle shells34that cooperate to define a handle portion36and a drive train or body portion38. In one embodiment, the body portion38includes a motor receiving portion and a transmission receiving portion. In one embodiment, the housing12is configured to be coupled to the electrical power source102. In one embodiment, the electrical power source102includes a battery pack or an AC power source as described in detail below.

In one embodiment, the output shaft68is proximate to the front end of the housing12and is coupled to the tool holder22for holding a power tool accessory. In one embodiment, the power tool accessory includes a tool bit such as a drill bit, an expansion bit, a screwdriver bit and/or other tool bits. In one embodiment, the tool holder22is a keyless chuck, although it should be understood that the tool holder can have other tool holder configurations such as a quick release tool holder, a hex tool holder, or a keyed tool holder/chuck. In one embodiment, the end effector22is coupled to the housing12and is configured to perform an operation on a workpiece (not shown).

In one embodiment, as shown inFIG.2, the output shaft68is configured to rotationally drive the tool holder22that is configured to receive the tool bit portion therein. In one embodiment, the output shaft68has a first end portion68aand an opposing second end portion68b. In one embodiment, one of the first end portion68aand the opposing second end68bportion is operatively connected to the second electrode44, and wherein the other of the first end portion68aand the opposing second end portion68bis operatively connected to the tool holder22.

In one embodiment, the trigger assembly24and the battery pack26are mechanically coupled to the handle portion36and are electrically coupled to the motor and transmission assembly14in a conventional manner that is not specifically shown but which is readily understood by and within the capabilities of one having an ordinary level of skill in the art. In one embodiment, the power tool10includes other sources of power (e.g., alternating current (AC) power cord or compressed air source) coupled to a distal end of the handle portion36. In one embodiment, the trigger assembly24is a variable speed trigger. In one embodiment, the trigger assembly24is configured to be coupled to the housing12for selectively actuating and controlling the speed of the motor15, for example, by controlling a pulse width modulation (PWM) signal delivered to the motor15.

In one embodiment, the motor15is disposed/received in the housing12and is configured to provide a torque to the input shaft66via the transmission assembly16. In one embodiment, the motor15is a brushless or electronically commutated motor, although the motor15may be another type of brushed DC motor or universal motor.

The motor15is housed in the motor receiving portion and includes a rotatable output motor shaft, which extends into the transmission receiving portion. In one embodiment, a motor pinion having a plurality of gear teeth is coupled for rotation with the rotatable output motor shaft. The trigger assembly24and battery pack26cooperate to selectively provide electric power to the motor and transmission assembly14in a manner that is generally well known in the art so as to permit the user of the power tool10to control the speed and direction with which the rotatable output motor shaft rotates.

In one embodiment, a motor output shaft extends from the motor15to the transmission16, which transmits power from the motor output shaft to the input member66, which transmits power to the output shaft68and to the tool holder22.

In one embodiment, the transmission assembly16comprises a multi-speed transmission having a plurality of gears and settings that allow the speed reduction through the transmission16to be changed, in a manner well understood to one of ordinary skill in the art. In one embodiment, the transmission assembly16comprises a multi-stage planetary gear set, with each stage having an input sun gear, a plurality of planet gears meshed with the sun gears and pinned to a rotatable planet carrier, and a ring gear meshed with and surrounding the planet gears. For each stage, if a ring gear is rotationally fixed relative to the housing12, the planet gears orbit the sun gear when the sun gear rotates, transferring power at a reduced speed to their planet carrier, thus causing a speed reduction through that stage. If a ring gear is allowed to rotate relative to the housing12, then the sun gear causes the planet carrier to rotate at the same speed as the sun gear, causing no speed reduction through that stage. By varying which one or ones of the stages have the ring gears are fixed against rotation, one can control the total amount of speed reduction through the transmission16, and thus adjust the speed setting of the transmission16(e.g., among high, medium, and low). In the illustrated embodiment, this adjustment of the speed setting is achieved via a shift ring that surrounds the ring gears and that is shiftable along the axis of the output shaft to lock different stages of the ring gears against rotation. In one embodiment, the power tool10includes a speed selector switch for selecting the speed reduction setting of the transmission. A speed selector switch is coupled to the shift ring by spring biased pins so that axial movement of the speed selector switch causes the axial movement of the shift ring. Further details regarding an exemplary multi-speed transmission is described in U.S. Pat. No. 7,452,304 which is incorporated by reference in the present patent application in its entirety. It should be understood that other types of multi-speed transmissions and other mechanisms for shifting the transmission among the speeds is within the scope of the present patent application.

In one embodiment, the power tool10includes the controller/control circuit50. In one embodiment, the control circuit50is disposed in the housing12and is operatively cooperable with the motor and transmission assembly14and the electrostatic clutch assembly18to control electrical power delivery from the electrical power source102to the motor and transmission assembly14and to the first and second electrodes42,44.

In one embodiment, the controller50is disposed in the housing12and is operatively cooperable with the motor and transmission assembly14and the electrostatic clutch assembly18to operate in the fully engaged mode, the fully disengaged mode, and the clutch mode.

In one embodiment, the controller50is further defined as a microcontroller. In other embodiments, controller refer to, be part of, or include an electronic circuit, an Application Specific Integrated Circuit (ASIC), a processor (shared, dedicated, or group) and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

In one embodiment, the controller50includes a current sensing circuit52, and a position sensing circuit54. In one embodiment, the current sensing circuit52includes a current sensor56(e.g., a shunt resistor) that senses the amount of current being delivered to the motor15and provides a current sensing signal corresponding to the sensed current to the controller50. In one embodiment, the position/rotation sensing circuit54includes one or more position/rotation sensors58that sense changes in the angular position of the motor output shaft and provides a signal corresponding to the angular rotation, speed, and/or acceleration of the motor15to the controller50. In one embodiment, the position sensors are Hall sensors that are already part of a brushless motor. For example, the power tool10may include a three-phase brushless motor, where the rotor includes a four-pole magnet, and there are three Hall sensors positioned at 120° intervals around the circumference of the rotor. As the rotor rotates, each Hall sensor senses when one of the poles of the four-pole magnet passes over the Hall sensor. Thus, the Hall sensors can sense each time the rotor, and thus the motor output shaft, rotates by an increment of 60°. In one embodiment, the rotation sensing circuit can use the signals from the Hall sensors to infer or calculate the amount of angular rotation, speed, and/or acceleration of the rotor. For example, the rotation sensing circuit includes a clock or counter that counts the amount of time or the number of counts between each 60° rotation of the rotor. The controller50can use this information to calculate or infer the amount of angular rotation, speed, and/or acceleration of the motor15. In one embodiment, the current sensing circuit52, the current sensor56, the position/rotation sensing circuit54, and the position/rotation sensors58are optional.

—In one embodiment, the electrostatic clutch assembly18is disposed in the housing12. In one embodiment, the electrostatic clutch assembly18is disposed in the housing12between the motor and transmission assembly14and the end effector22.

In one embodiment, the electrostatic clutch assembly18includes the first electrode42operatively connected to the motor and transmission assembly14and the second electrode44operatively connected to the output shaft68.

In one embodiment, the electrostatic clutch assembly18includes the input member66configured to be rotationally driven by the motor and transmission assembly14, the output member68configured to rotationally drive the end effector22, the first electrode42electrically couplable to the electrical power source102, the second electrode44electrically couplable to the electrical power source102, and the dielectric layer106separating the first electrode42from the second electrode44.

In one embodiment, the first electrode42is operatively connected to the motor and transmission assembly14via the input member/shaft66. In one embodiment, the first electrode42is operatively connected to the motor15via the input shaft66that is driven by the motor and transmission assembly14.

In one embodiment, the second electrode44is operatively connected to the output shaft68. In one embodiment, the first electrode/rotating input electrode42is coupled to the rotating input shaft66that is driven by the transmission16and the second electrode/the rotating output electrode44is coupled to the rotating output shaft68that drives the output tool holder/chuck22.

Each of the facing surfaces70,72of the input electrode42and the output electrode44are coated with the electrostatic layer/film60. In one embodiment, each of the first electrode42and the second electrode44includes conductive material disposed on at least a portion thereof. In one embodiment, the conductive material is disposed beneath surfaces70,72of the first electrode42and the second electrode44that face each other.

In one embodiment, each of the first electrode42and the second electrode44includes at least one conductive material layer. In one embodiment, at least one conductive material layer is disposed on surfaces of the first electrode42and the second electrode44that face each other. In one embodiment, the electrostatic clutch18is composed of a plurality of layers of electrostatic film60that are layered on top of one another for greater holding force.

In one embodiment, each of the first electrode42and the second electrode44includes a substrate45and an electrostatic layer/coating/film60deposited thereon. In one embodiment, each of the electrodes42,44and/or the electrostatic layer/coating/film60comprise a lightweight conductive material, such as aluminum-sputtered biaxially-oriented polyethylene terephthalate.

In one embodiment, the electrode42,44is comprised of aluminum-sputtered BOPET (Bi-axially Oriented Polyethylene Terephthalate) film, also known as Mylar® film. The aluminum deposition acts as the conductive layer60and the BOPET acts as the substrate45. Aluminum-sputtered BOPET films of this type can have a thickness of around 25 microns. Despite the thin profile, the material is sufficiently strong to act as a force transmission component. In addition, very little electrode material is required to hold a charge, making thin and lightweight electrodes42,44possible. In alternative embodiments, a single-layer, conductive electrode, such as a metallic foil, is used.

In one embodiment, with a pair of electrodes, at least one electrode42,44is covered in a dielectric material/layer106to maintain the gap between the conductive surfaces of the electrodes42,44. In one embodiment, the two electrostatic films60are always separated by the dielectric layer106. In one embodiment, the dielectric layer is very thin and has dimension in the order of microns.

In one embodiment, the dielectric layer106is an air gap between the two electrostatic films60. In one embodiment, if the dielectric layer106is an air gap, then there may be a slightly larger air gap when the electrodes42,44are not energized and a smaller air gap when the electrodes42,44are energized.

For example, in one embodiment, when the electrodes42,44are energized, the dielectric layer106of one electrode42,44is configured to touch the other electrode42,44. In one embodiment, when the electrodes42,44are energized, the dielectric layer106of one electrode42,44is configured to touch the dielectric layer106of the other electrode42,44.

In one embodiment, when the electrodes42,44are deenergized, there may be an air gap between the dielectric layer106on one electrode42,44and the other electrode42,44. In one embodiment, when the electrodes42,44are deenergized, there may be an air gap between the dielectric layer106on one electrode42,44and the dielectric layer106on the other electrode42,44.

In one embodiment, as shown inFIGS.2-11, the electrodes42,44are generally planar. In one embodiment, as shown inFIGS.2-11, the electrodes42,44generally have annular plate/disc shaped configurations. In one embodiment, as shown inFIGS.2-11, each of the first electrode42and the second electrode44includes an annular plate member. The first electrode42and the second electrode44may interchangeably be referred to as input electrode/disc/plate and output electrode/disc/plate, respectively.

In one embodiment, as shown inFIGS.12A-12C, the electrodes442,444have coaxial cylindrical configurations to maximize the surface area between the electrodes442,444. In one embodiment, first electrode442and the second electrode444may interchangeably be referred to as input electrode/tube and output electrode/tube, respectively.

In one embodiment, the electrostatic clutch assembly18includes a plurality of clutch settings. In one embodiment, each clutch setting corresponds to a desired output operation of the power tool. That is, the clutch setting of the electrostatic clutch18can be set by the user based on a desired output operation. For example, the desired output operation can include an amount of material to be removed from a workpiece. In one embodiment, each clutch setting has the set torque. In one embodiment, each clutch setting is associated with a different clutch disengage torque (i.e., a torque at which the electrostatic clutch assembly disengages to thereby prevent the transmission of torque transmission between the motor and transmission assembly14and the output shaft68). In one embodiment, each predetermined clutch setting includes a maximum clutch setting, a minimum clutch setting, and a plurality of intermediate clutch settings between the maximum and minimum clutch settings. In one embodiment, each predetermined clutch setting includes its associated engaged configuration, and its associated disengaged configuration.

The power tool further includes a clutch setting switch or collar that is used to adjust a clutch setting of the electrostatic clutch. In one embodiment, when the user is able to control the amount of slip or rotate, e.g., via the clutch setting switch or collar.

In one embodiment, as shown inFIG.2, the electrostatic clutch18includes positive and negative brushes74,76. In one embodiment, the first electrode42and the second electrode44are coupled to one or more positive and negative brushes, respectively, at the end portions of the electrodes. For example, in one embodiment, the first electrode42is coupled to a negative brush76at one end thereof and the second electrode44is coupled to a positive brush74at one end portion thereof. As shown inFIG.2, the positive brush74of one of the electrodes42,44is disposed next to the negative brush76of the other of the electrodes42,44. In one embodiment, the positive and negative brushes74,76are stationary relative to the tool housing12. In one embodiment, the positive and negative brushes74,76are configured to provide electrical current to charge the respective electrostatic layer/films60and/or the respective electrodes42,44. In one embodiment, the electrostatic clutch assembly18is configured provide an electrical charge to the first electrode42and/or the second electrode44when the electrostatic clutch assembly18is in either the fully engaged mode or the clutch mode. The positive and negative brushes in the embodiments ofFIGS.7and10-11may have a similar configuration and operation as positive and negative brushes74,76inFIG.2.

In one embodiment, as shown in and described in detail with respect toFIGS.2-6and13, the electrostatic clutch assembly18includes the opposing plates/electrodes42,44. When a voltage or a current is applied to the electrodes42,44, the electrodes42,44are charged and electrostatically attract, such that above a threshold of the applied voltage the electrodes42,44fully couple so that they will rotate together. Below a threshold of the applied voltage/current, the electrodes42,44fully decouple so that they can rotate relative to one another. And, between those thresholds of the applied voltage/current, the electrodes42,44variably attract, allowing for relative slip or rotation between them based upon the applied torque. In one embodiment, the transitions between the states of the fully engaged, the clutch, and fully disengaged modes have an observable electrical signature/signal by a sensor that may be observed by the tool's control module(s)/controller50, such that a response to this may be ceasing rotation of the power tool's motor15. In one embodiment, the torque transfer function is descriptively a function of charge rather than voltage. The electrodes in the embodiments ofFIGS.7and10-11may have a similar configuration and operation as electrodes42,44inFIG.2.

In one embodiment, the electrostatic clutch assembly18/218/318includes a pair of annular disks/electrodes42,44or242,244or342,344as shown in and described in detail with respect toFIGS.2-5,7-9B and10-11. In one embodiment, the electrostatic clutch assembly418includes a pair of coaxial cylindrical tubular electrodes442,444for maximizing surface area of the electrostatic clutch418for implementation in a tool with a transmission as shown in and described in detail with respect toFIGS.12A-12C. In one embodiment, the electrostatic clutch assembly218/418includes a composition of the electrostatic attractive plates/electrodes242,244or442,444with the electrostatic layers/films260/460and the brake pad262/462as shown in and described in detail with respect toFIGS.7-9B and12A-12C.

When the electrostatic layers/films60are de-energized and/or the electrostatic clutch18is in its fully disengaged mode, as shown inFIG.3, there is a gap G between the electrodes42,44and their respective electrostatic films/layers60. In one embodiment, the gap G includes an air gap between the dielectric materials/layers of each of the electrostatic films/layers60. In one embodiment, the gap G includes an air gap between one of the electrostatic films/layers60and the dielectric material/layer of the other of the electrostatic films/layers60. In another embodiment, the gap G includes a dielectric air gap between the electrostatic films/layers60and an additional air gap AG.

In one embodiment, as shown inFIGS.4and5, when electrical current is applied to the electrostatic films/layers60(with opposite polarity as shown inFIG.2), the electrostatic clutch assembly18is in its fully engaged mode/in its clutch mode and the electrostatic films/layers60attract one another and the electrodes42,44move axially so that there is no gap or a very tiny gap between them.

In one embodiment, as shown inFIG.4, when electrical current is applied to the electrostatic films/layers60(with opposite polarity as shown inFIG.2), the electrostatic clutch assembly18is in its fully engaged mode and the electrostatic films/layers60attract one another and the electrodes42,44move axially so that there is substantially no gap (i.e., only dielectric material layer or a dielectric air gap) between them.

In one embodiment, as shown inFIG.5, when electrical current is applied to the electrostatic films/layers60, the electrostatic clutch assembly18is in its clutch mode and the electrostatic films/layers60attract one another and the electrodes42,44move axially so that there is a very tiny gap (i.e., only dielectric material layer or a dielectric air gap) between them.

In one embodiment, the electrodes42,44are configured to move axially due to small tolerance stack-ups in the transmission16and other mechanical components. In one embodiment, the electrodes42,44are also configured to be biased apart (e.g., may include a spring compressing the layers) from one another by a very light spring (not shown) disposed between them.

In one embodiment, the electrostatic clutch assembly18is provided in the power tool10such that when an electric field is applied to the electrodes42,44, the opposing electrodes42,44attract by the mechanism of electrostatic attraction and providing a holding force between the electrodes42,44. In one embodiment, the electric field includes a voltage or a current. In one embodiment, the applied voltage is less than 1 kilo Volts (kV).

In one embodiment, the controller50is operatively cooperable with the motor and transmission assembly14and the electrostatic clutch assembly18to operate in the fully engaged mode wherein an electric field above a first predetermined threshold is applied across the first electrode42and the second electrode44causing a first electrostatic force between the first electrode42and the second electrode44to rotationally couple the output shaft68with the motor15such that the output shaft68, the input shaft66, and the motor and transmission assembly14move together at the same velocity. In this configuration, as shown inFIG.4, the respective shafts66,68(i.e., connected to the opposing electrodes42,44) operate at the same speed. For example, both the shaft66connected to the electrode42and the shaft68connected to the electrode44rotate at 2 k RPM. This speed disclosed is exemplary and not intended to be limiting in anyway. This configuration may be referred to as the fully engaged mode, the drill and hammer drill mode/configuration, or the full holding force configuration of the electrostatic clutch18.

In one embodiment, when the electrostatic clutch assembly18is in the fully engaged mode, the first electrode42and the second electrode44of the electrostatic clutch assembly18are attracted to each other. In one embodiment, as shown inFIG.4, when the electrostatic clutch assembly18is in the fully engaged mode, the first electrode42and the second electrode44of the electrostatic clutch assembly18are positioned in such a way that no gap (i.e., only dielectric material layer or a dielectric air gap) exists between surfaces of the first electrode42and the second electrode44that face each other.

In one embodiment, the controller50is operatively cooperable with the motor and transmission assembly14and the electrostatic clutch assembly18to operate in the fully disengaged mode wherein an electric field below a second predetermined threshold between the first electrode42and the second electrode44causes the output shaft68to be rotationally decoupled from the motor and transmission assembly14and input shaft66. As shown inFIG.3, when the electric field is removed from or is not applied to the electrodes42,44, the electrodes42,44do not have electrostatic attraction therebetween and the electrodes42,44are decoupled allowing independent rotation of their respective shafts66,68. This configuration may be referred to as the fully disengaged mode/configuration or a full decoupling configuration of the electrostatic clutch18.

In one embodiment, when the electrostatic clutch assembly18is in the fully disengaged mode, there is no electrostatic charge present between the first electrode42and the second electrode44of the electrostatic clutch assembly18. In one embodiment, when the electrostatic clutch assembly18is in the disengaged mode, the first electrode42and the second electrode44of the electrostatic clutch assembly18are not attracted to each other. In one embodiment, when the electrostatic clutch assembly18is in the fully disengaged mode, the first electrode42and the second electrode44of the electrostatic clutch assembly18are positioned in such a way that a gap G (as shown inFIG.3) exists between surfaces of the first electrode42and the second electrode44that face each other. In one embodiment, as discussed in detail above, the gap G includes a dielectric (air or material) gap106between the electrostatic films/layers60and the additional air gap AG.

In one embodiment, the controller50is operatively cooperable with the motor and transmission assembly14and the electrostatic clutch assembly18to operate in the clutch mode wherein an electric field between the first predetermined threshold and the second predetermined threshold is applied across the first electrode42and the second electrode44causing a second electrostatic force between the first electrode42and the second electrode44to rotationally couple the output shaft68with the input shaft66and the motor and transmission assembly14such that the output shaft68moves together at the same velocity as the input shaft66and the motor and transmission assembly14when the torque therebetween is below a set torque, and permits the output shaft68to rotate at a lower or zero speed relative to the input shaft66and motor15when the torque therebetween is above the set torque. In between the full engaged configuration ofFIG.4and the full disengaged mode ofFIG.3, a variable electric field is applied to the electrodes42,44that produces a holding torque where the application/applied torque below a predetermined/set value the electrodes42,44are coupled, but where the application/applied torque exceeds the predetermined/set value, the electrodes42,44slip or rotate relative to one another, thereby limiting the torque application at the working bit. This configuration may be referred to as the clutch mode. In this configuration, as shown inFIG.5, the respective shafts66,68(i.e., connected to the opposing electrodes42,44) operate at the different speeds. For example, the shaft66connected to the electrode42rotates at 2 k RPM, while the shaft68connected to the electrode44rotates at 0-10 RPM. These speeds disclosed are exemplary and not intended to be limiting in any way.

In one embodiment, when the electrostatic clutch assembly18is in the clutch mode and when the torque between the output shaft68and the motor and transmission assembly14is above the set torque, the velocity of the output shaft66is zero. In one embodiment, when the electrostatic clutch assembly18is in the clutch mode, the first electrode42and the second electrode44of the electrostatic clutch assembly18are variably attracted to each other. In one embodiment, as shown inFIG.5, when the electrostatic clutch assembly18is in the clutch mode, the first electrode42and the second electrode44of the electrostatic clutch assembly18are positioned in such a way that no gap (i.e., only dielectric material layer or a dielectric air gap) exists between surfaces of the first electrode42and the second electrode44that face each other.

In one embodiment, the clutch mode includes a first mode of operation and a second mode of operation.

In the first mode of operation, the control circuit50causes a first voltage to be applied across the first electrode42and a second voltage with a polarity opposite a polarity the first voltage to be applied to the second electrode44, generating a first attractive force between the first and second electrodes42,44, which causes the output member68to rotate together with the input member66when a torque on the output member68is less than or equal to a first threshold value (e.g., when the torque on the output member is such that a shear force or torque about the rotational axis of the output shaft is less than or equal to the attractive force between the electrodes) and which causes the output member68to rotationally slip relative to the input member66when the torque on the output member68exceeds the first threshold value (e.g., when the torque on the output member is such that a shear force or torque about the rotational axis of the output shaft is greater than the attractive force between the electrodes), interrupting torque transmission from the input member66to the output member68. In one embodiment, the first threshold corresponds to the first attractive force.

In one embodiment, in the second mode of operation, the control circuit50causes a third voltage to be applied across the first electrode42and a fourth voltage with a polarity opposite a polarity the third voltage to be applied to the second electrode44, generating a second attractive force between the first and second electrodes42,44, which causes the output member68to rotate together with the input member66when a torque on the output member68is less than or equal to a second threshold value and which causes the output member68to (e.g., rotationally) slip or rotate relative to the input member66when the torque on the output member68exceeds the second threshold value, interrupting torque transmission from the input member66to the output member68. That is, in one embodiment, in the second mode of operation, the control circuit50causes the third voltage to be applied to the first electrode42and a different fourth voltage to be applied to the second electrode44.

In one embodiment, the third voltage is greater than the first voltage, the fourth voltage is greater than the second voltage, the second attractive force is greater than the first attractive force, and the second threshold value is greater than the first threshold value. In one embodiment, a second voltage difference between the third voltage and the fourth voltage is greater than a first voltage difference between the first voltage and the second voltage.

In one embodiment, as shown inFIG.13, the power tool10further comprising a selector switch104coupled to the housing12that is actuatable by a user to select between the first and second modes of operation.

In one embodiment, in a third mode of operation, the control circuit50causes a zero voltage difference to be applied to the first and second electrodes42,44, allowing the second electrode to rotate relative to the first electrode and preventing torque transmission from the input member66to the output member68. In one embodiment, the control circuit50is configured to automatically switch from the first mode to the third mode upon sensing (e.g., by a sensor) that the output member68has rotationally slipped or rotated relative to the input member66.

In one embodiment, in a fourth mode of operation, the electrostatic clutch assembly18is configured to prevent interruption of torque transmission from the input member66to the output member68.

In one embodiment, in the fourth mode of operation, the control circuit may cause a fifth voltage to be applied across the first electrode42and a different sixth voltage to be applied to the second electrode44, generating a third attractive force between the first and second electrodes42,44, the third attractive force exceeding a torque on the output member68during operation of the power tool10. The second voltage may have a polarity opposite a polarity of the first voltage. In one embodiment, the first voltage difference is user selectable to adjust the first attractive force and the first threshold value. In one embodiment, a greater voltage difference corresponds to a greater first attractive force and a greater first threshold value.

In one embodiment, the electrostatic clutch assembly18is held in the clutch mode such that when the working element meets a dynamic impact event, the electrostatic clutch18slips or rotates. Thus, this configuration provides protection to the elements of the power tool, e.g., a mower blade striking a rock.

When energized, the electrodes/discs42,44rotate together as a unit until the output torque on the chuck/tool holder22exceeds the holding force of the electrostatic films/layers60. At this time, the electrodes/discs42,44rotate relative to one another with only a small frictional force between them. The input shaft66and the input disc42will continue to rotate, while the output disc44coasts to rest.

In one embodiment, depending on the amount of voltage or current applied to the electrostatic films/layers60, the charge and their holding force can vary. Thus, there can be different clutch settings for different amounts of voltage or current applied to the electrostatic films/layers60. This is indicated by clutch settings1,2, and3and lines A, B and C inFIG.6.FIG.6shows a graphical representation of the various working bit speeds at different clutch settings of the system/power tool10of the present patent application. The working bit speeds (i.e., measured in revolutions/minute (RPM)) at different clutch settings in the clutch mode are shown on the left-hand side Y-axis of the graph inFIG.6and the applied torque (i.e., measured in Nm) are on the X-axis of the graphFIG.6. As shown inFIG.6, at each different clutch setting, the working bit speed drops fast/instantaneously/drastically (from speed A1to speed A2at a first torque corresponding to clutch setting1, from speed B1to speed B2at a torque corresponding to clutch setting2, and from speed C1to speed C2at a torque corresponding to clutch setting3), where the applied voltage corresponding to the torque at which the electrostatic clutch18begins to slip or rotate is different for different clutch settings (e.g., greater applied voltage corresponds to greater torque or clutch setting).

In one embodiment, the power tool/system10includes a sensor that senses when the electrostatic clutch18slips or rotates (e.g., a current sensor or a rotational motion/position sensor that are described above)) and that causes the control circuit/controller50to de-energize the electrostatic films/layers60after the electrostatic clutch18slips or rotates. In one embodiment, the power tool/system10includes a sensor configured to sense whether the electrostatic clutch assembly18is in the fully engaged mode, the fully disengaged mode, or the clutch mode and output a signal to the controller50. In one embodiment, the controller50, in response to the received signal from the sensor, is configured to stop the rotation of the motor and transmission assembly14. The sensor may comprise one or more of a current sensor, a position sensor, and a rotational motion sensor.

In one embodiment, the power tool10further comprises a selector switch104(as shown inFIG.13) actuatable by a user to select between the first and second modes of operation. In one embodiment, in a third mode of operation, the control circuit50causes zero voltage to be applied to the first and second electrodes, preventing motion from being transmitted from the input member66to the output member68. In one embodiment, the control circuit50is configured to automatically switch from the first mode to the third mode upon sensing that the motion transmission from the input member66to the output member68has been interrupted.

In one embodiment, the power tool system10includes a sensor that senses when the electrostatic clutch18slips or rotates (e.g., a current sensor or a rotational motion sensor as described above) and that causes the control circuit/controller50to de-energize the electrostatic films/layers60after the electrostatic clutch assembly18slips or rotates.

In another embodiment, as shown inFIGS.7-9B, the present patent application provides the electrostatic clutch assembly218that may include the input member266, the output member268, at least one frictional surface262, the first electrode242, the second electrode244, the dielectric layer206, and a control circuit250. The input member266is configured to be selectively driven in motion. The output member268is configured to selectively output a motion. The first electrode242is electrically couplable to the electrical power source202. The second electrode244is electrically couplable to the electrical power source202. The dielectric layer206is separating the first electrode242and the second electrode244. The control circuit250is operatively cooperable with the motor and transmission assembly214and the first and second electrodes242,244to control electrical power delivery from the electrical power source202to the motor and transmission assembly214and to the first and second electrodes242,244. In a first mode of operation, the control circuit250causes a voltage difference to be applied across the first and second electrodes242,244, generating a first attractive force between the first and second electrodes242,244. For example, a first voltage may be applied across the first electrode242and a second voltage with a polarity opposite a polarity the first voltage may be applied to the second electrode244, generating a first attractive force between the first and second electrodes242,244, which causes the frictional surface262to frictionally engage with at least one of the input member266and the output member268to enable motion to be transmitted from the input member266to the output member268. In one embodiment, the at least one frictional surface262of the electrostatic clutch assembly218is a brake pad that engages one or both of the input and output members266,268when the electrodes242,244are energized.

FIGS.7-9Bshow another embodiment of the present patent application that differs from the embodiment inFIGS.2-5in that the input rotating disc242and the output rotating disc244are/have brake pads or have other frictional materials/surfaces that face one another. Other than this difference, the power tool system200with the electronic clutch218inFIGS.7-9Bhas many of the same elements and the same operation as the power tool system10with the electronic clutch18shown inFIGS.2-5so that those similar elements and the operation of this embodiment of the power tool system200will not be described in detail.

In one embodiment, as shown inFIGS.8A and8B, each of the first electrode242and the second electrode244includes a brake pad262disposed on at least a portion thereof. In one embodiment, each electrode242,244has a central opening267therein to receive and connect with their respective shafts266,268. In one embodiment, each electrode242,244has a brake pad portion269surrounding the central opening267. In one embodiment, the brake pad portion269has the brake pad (material)262. In one embodiment, each electrode242,244has an electrostatic portion271surrounding the brake pad portion269. In one embodiment, the electrostatic portion271has the electrostatic (material) film/layer260. As shown inFIGS.8A and8B, the brake pads262are surrounded by annular discs that carry facing electrostatic films/layers260that rotate together with the brake pads262.

In one embodiment, the frictional materials/surfaces comprise brake pads262. In various embodiments, different materials can be used to create friction between the input rotating disc242and the output rotating disc244when they contact one another. Such materials can include ceramics, metal materials (e.g., steel), rubber materials, Kevlar, and/or carbon compounds on one or both of the contacting surfaces.

When the electrostatic clutch218is in its fully disengaged mode and the electrostatic films/layers260are de-energized, there is a gap G (as shown inFIG.9B) between both the brake pads262i,262oand the electrostatic films/layers260so that no torque is transmitted. In one embodiment, the gap between the electrostatic films/layers260includes an air gap between the dielectric materials/layers of each of the electrostatic films/layers260. In one embodiment, the gap between the electrostatic films/layers260includes an air gap between one of the electrostatic films/layers260and the dielectric material/layer of the other of the electrostatic films/layers260. In another embodiment, the gap between the electrostatic films/layers260includes a dielectric air gap between the electrostatic films/layers260and the additional air gap AG.

In one embodiment, as shown inFIG.9B, when the electrostatic clutch assembly218is in the fully disengaged mode, the electrostatic layers260of the electrodes242,244are separated from each other. In this fully disengaged mode, the electrostatic layers260of the electrodes242,244are separated by the dielectric material layer or the dielectric air gap206and the additional air gap AG. Also, when the electrostatic clutch assembly218is in the fully disengaged mode, the brake pads262on the electrodes242and244are also separated from each other. That is, in one embodiment, when the electrostatic clutch assembly218is in the fully disengaged mode, the frictional force(s) between the frictional surfaces of the electrodes242,244are relieved by some/slight axial relative movement (e.g., movement in the axial direction) of the components of the electrostatic clutch assembly218and/or other the components of the power tool that are positioned between the motor and transmission assembly2142and the chuck222. In one embodiment, such axial movement of the components may be achieved using a spring force. For example, the frictional forces between the electrodes242and44can be relieved, in the fully disengaged mode, by biasing the electrodes242and244apart from one another by a light spring force (not shown) that operates to bias one or both of the electrodes242/244away from the other. The spring force can be created using a mechanical spring (e.g., coil spring, tension spring, leaf spring, etc.). In another embodiment, such axial movement of the components may be achieved using other energy or force types, such as electrical, electromechanical, and/or electromagnetic. In another embodiment, such axial movement of the components may be achieved without application of any force, but rather simply be a passive movement resulting only from a release of electrostatic forces between the electrodes, permitted the friction surfaces to separate.

When the electrostatic films/layers260are energized with opposite polarity by the stationary brushes274,276(as shown inFIG.7) and when the electrostatic clutch assembly218is in either its fully engaged mode or its clutch mode, the input disc242and the output disc244are drawn/attracted toward one another.

As shown inFIG.9A, the brake pads262i,262oengage each other so that there is no gap between the brake pads262i,262owhen the electrostatic clutch assembly218is in its fully engaged mode. In one embodiment, the electrostatic films/layers260touch or there may be a tiny gap (i.e., dielectric material or dielectric air gap) between the electrostatic films/layers260when the electrostatic clutch assembly218is in its fully engaged mode.

In one embodiment, as shown inFIG.9A, when the electrostatic clutch assembly218is in the fully engaged mode, the electrostatic layers260of the electrodes242,44are held in contact with each other due to a holding/an attractive/an electrostatic force therebetween generated due to the electric field applied to the electrodes242,244. In one embodiment, in this fully engaged mode, the electrostatic layers260of the electrodes242,244are separated by the dielectric material layer or the dielectric air gap206. Also, when the electrostatic clutch assembly218is in the fully engaged mode, the brake pads262on the electrodes242,244are held in contact with each other due to a friction force therebetween. That is, in one embodiment, when the electrostatic clutch assembly218in the fully engaged mode, the electrodes242,244(e.g., the brake pads262thereof) are disposed in contact with each other, with a combination of the holding/attractive/electrostatic force and the frictional force therebetween. In one embodiment, the amount of the holding/attractive/electrostatic force between the electrodes242/244is configured to be adjusted by adjusting the electric field (e.g., voltage or current) applied thereto. In one embodiment, the amount of the frictional force between the electrodes242/244may optionally also be adjusted. For example, the electrostatic clutch assembly218may include a tension adjustment mechanism that is operated to adjust the amount of the frictional force between the electrodes242/244. That is, in one embodiment, when the electrostatic clutch assembly218is in the fully engaged mode, the electrodes242,244are held in contact with each other by adjusting the frictional force therebetween, the attractive/electrostatic force therebetween, or any combination of the frictional force and the attractive/electrostatic force therebetween.

In one embodiment, the tension adjustment mechanism of the electrostatic clutch assembly218is operated to adjust the amount of the frictional force between the electrodes242/244so as to relieve the frictional forces between the electrodes242/244when the electrostatic clutch assembly218is in the fully disengaged mode.

Similarly, in one embodiment, the electrostatic films/layers260touch or there may be a tiny gap (i.e., dielectric material or dielectric air gap) between the electrostatic films/layers260and there is no gap between brake pads262i,262owhen the electrostatic clutch218is in its clutch mode. Also, in the clutch mode of the electrostatic clutch assembly218, the output brake pad262oslips or rotates relative to the input brake pad262iwhen the output torque overcomes the frictional force between the brake pads262i,262oand the holding force of the energized electrostatic films/layers260.

In one embodiment, the clutch mode of the power tool includes a first mode of operation and a second mode of operation.

In one embodiment, in the first mode of operation, the control circuit250causes a first voltage to be applied across the first electrode242and a second voltage with a polarity opposite a polarity the first voltage to be applied to the second electrode244, generating a first attractive force between the first and second electrodes242,244, which causes the frictional surface262to frictionally engage with at least one of the input member266and the output member268to enable motion to be transmitted from the input member266to the output member268. In one embodiment, this embodiment, is generally directed to an electrostatic clutch assembly218, regardless of whether it is in a power tool. In one embodiment, the at least one frictional surface262of the electrostatic clutch assembly218is a brake pad that engages one or both of the input and output members266,268when the electrodes242,244are energized.

In one embodiment, in the first mode of operation, motion from the input member266to the output member268is interrupted when a force applied to the output member268is greater than a first threshold value. In one embodiment, the first threshold value corresponds to a frictional force between the frictional surface262and at least one of the input member266and the output member268.

In one embodiment, in the second mode of operation, the control circuit250causes a third voltage to be applied across the first electrode242and a fourth voltage with a polarity opposite a polarity the third voltage to be applied to the second electrode244, generating a second attractive force between the first and second electrodes242,244, which causes the frictional surface to frictionally engage with at least one of the input member266and the output member268to enable motion to be transmitted from the input member266to the output member268when a force applied to the output member268is less than or equal to a second threshold value and the to interrupt force transmission from the input member266to the output member268when the force applied to the output member268is greater than the second threshold value.

In one embodiment, the third voltage is greater than the first voltage, the fourth voltage is greater than the second voltage, the second attractive force is greater than the first attractive force, and the second threshold value is greater than the first threshold value.

The embodiment ofFIGS.7-9Bis different from the embodiment ofFIGS.2-5insofar as the primary wear surfaces are the brake pads262(262i,262o) in the embodiment ofFIGS.7-9B, and the primary wear surfaces are the electrostatic films/layers60in the embodiment ofFIGS.2-5.

FIGS.10-11show another embodiment of the present patent application that differs from the embodiment inFIGS.2-5in that the input rotating disc342and the output rotating disc344are/have brake pads or have other frictional materials/surfaces that face one another and the power tool system300also includes thrust bearings364as described in detail below. Other than these differences, the power tool system300with the electronic clutch assembly318inFIGS.10-11has many of the same elements and the same operation as the power tool system10with the electronic clutch assembly18shown inFIGS.2-5so that those similar elements and the operation of this embodiment of the power tool system300will not be described in detail.

As shown inFIGS.10-11, the power tool system300includes the input disc342rotating with the input shaft366and the output disc344rotating the output shaft368and the input rotating disc342and the output rotating disc344may have frictional surfaces or brake pads that face one another. In one embodiment, the rear sides/surfaces of the discs342,344are engaged by the thrust bearings364(e.g., ball thrust bearings) that are rotationally stationary but axially moveable relative to the housing312. In one embodiment, the thrust bearings364are coupled to the electrostatic films/layers360that are stationary relative to the housing312.

In one embodiment, referring toFIGS.10-11, each of the first electrode342and the second electrode344includes an annular member342/344, a thrust bearing364, and an electrostatic film member360. In one embodiment, referring toFIGS.10-11, the dielectric layer306separates the electrostatic film members360. In one embodiment, the thrust bearing364of each of the first electrode342and the second electrode344is operatively connected to the associated annular member342/344and the associated electrostatic film member360. In one embodiment, the annular members342,344of the first electrode342and the second electrode344are operatively connected to the motor and transmission assembly and the output shaft368, respectively. In one embodiment, each of the first electrode342and the second electrode344includes a brake pad362disposed on at least a portion of the annular member342,344. In one embodiment, each annular member342,344has a central opening367therein to receive and connect with their respective shafts366,368.

When the electrostatic clutch318is in either its fully engaged mode or its clutch mode, and the electrostatic films/layers360are energized, the thrust bearings364push thrust plates toward one another, bringing the input and output discs342,344into frictional contact with each other. There may be no gap or a tiny gap (e.g., a dielectric material/dielectric air gap) between the electrostatic films/layers360. There is also no gap between the input disc342and the output disc344. At the same time, the discs342,344are permitted to rotate relative to the thrust bearings64. In the clutch mode of the electrostatic clutch318, the output disc344will slip or rotate relative to the input disc342when the output torque overcomes the frictional force between the discs342,344and the holding force of the energized electrostatic films/layers360.

When the electrostatic clutch318is in its fully disengaged mode and the electrostatic films/layers360are de-energized, the electrostatic films/layers360separate and the thrust bearings364no longer push the thrust bearings364toward one another, allowing the frictional surfaces to separate (which may be further facilitated by a light spring or elastic member acting on one or both of the input member and output member to bias them apart from one another). There is a gap (e.g., a dielectric material/dielectric air gap and the additional air gap AG) between the electrostatic films/layers360and also there is a gap between the input disc342and the output disc344.

In one embodiment, the power tool system300has a sensor that senses when the electrostatic clutch318slips or rotates (e.g., a current sensor or a rotational motion sensor) and that causes the control circuit/controller to de-energize the electrostatic films/layers360after the electrostatic clutch318slips or rotates.

This embodiment ofFIGS.10-11is different from the first embodiment ofFIGS.2-5insofar as the primary wear surfaces in the embodiment ofFIGS.10-11are brake pads362, and the primary wear surfaces are the electrostatic films/layers60in the embodiment ofFIGS.2-5.

FIGS.12A-12Cshow another embodiment of the present patent application that differs from the embodiment inFIGS.2-5in that brake pads462and electrostatic films/layers460are arranged on facing surfaces of concentric input and output cylinders442,444. Other than these differences, the power tool system400with the electronic clutch assembly418inFIGS.12A-12Chas many of the same elements and the same operation as the power tool system10with the electronic clutch assembly18shown inFIGS.2-5so that those similar elements and the operation of this embodiment of the power tool system400will not be described in detail.

In one embodiment, the electrostatic clutch assembly418includes electrostatic films460that are arranged on facing surfaces of the concentric input and output cylinders442,444. In one embodiment, the electrostatic clutch assembly418includes the dielectric layer (e.g., dielectric material or dielectric air gap)406that separates electrostatic films460.

In another embodiment, the electrostatic clutch assembly418includes a combination of the electrostatic films460and the brake pads462that are arranged on facing surfaces of the concentric input and output cylinders442,444. In one embodiment, the electrostatic clutch assembly418includes the dielectric layer (e.g., dielectric material or dielectric air gap)406that separates electrostatic films460.

In one embodiment, as shown inFIGS.12A-12C, one of the first electrode442and the second electrode444includes a cylindrical member443c1and the other of the first electrode442and the second electrode444includes a different diameter coaxial cylindrical member443c2received within the cylindrical member443c1.

In the illustrated embodiment ofFIGS.12A-12C, the outer cylindrical member/electrode is configured to rotationally drive the end effector and the inner cylindrical member/electrode is configured to be rotationally driven by the motor and transmission assembly. In another embodiment, the inner cylindrical member/electrode is configured to rotationally drive the end effector and the outer cylindrical member/electrode is configured to be rotationally driven by the motor and transmission assembly.

In one embodiment, in order for the brake pads462to be able to separate from each other, the outer cylinder444would be made with a break to be two half cylinders so that the outer cylinder444can move radially outward from the inner cylinder444. In this embodiment, the input cylinder442and the output cylinder444each could be either the inner cylinder442or the outer cylinder444. This embodiment ofFIGS.12A-12Crequires the use of stationary brushes474,476that were discussed in detail above with respect toFIG.2-5.

That is, the embodiment ofFIGS.12A-12Cis same concept as the embodiment ofFIGS.2-5, but instead of an annular plate arrangement of the embodiment inFIGS.2-5, the electrostatic clutch assembly418is configured as two coaxial cylinders442,444where the attractive clutch force is radial. The benefit of this arrangement is to increase surface area by making use of the entire length of the transmission of the drill400.

In one embodiment, as shown inFIGS.14-17, an electrostatic clutch assembly518acts as a brake providing the saw braking mechanism/system/functionality590. In one embodiment, the saw braking system590is used in the power tool500as shown inFIG.14. In one embodiment, the power tool500, as shown inFIG.14, is a (portable) circular saw500as shown inFIG.14. In another embodiment, the saw braking system590is used in other power tools, such as power miter saw, power circular saw, power reciprocating saw, power table saw, power grinder, power sagittal saw, etc.

In one embodiment, the power tool500generally includes a controller, a motor and transmission assembly to drive a saw blade592, typically through a reduction gearing/transmission, a drive shaft597connected to the motor and transmission assembly, the saw blade592mounted on the drive shaft597, the power source (battery or AC power) operatively connected to the motor and transmission assembly and the controller, a handle594, and a blade guard598(as shown inFIGS.15-17). In one embodiment, the blade guard598substantially encloses the saw blade592. These power tools may include other components that are not discussed in detail here. In one embodiment, the power tool500also includes the saw braking system590with the electrostatic clutch assembly518.

In one embodiment, as shown inFIGS.15-17, the electrostatic clutch assembly518includes opposing plates/electrodes542,544and the dielectric layer (i.e., dielectric material or air gap)506that separates the electrodes542,544. When a voltage, a current or an electric field is applied, the electrodes542,544electrostatically attract, such that above a threshold of the applied voltage the electrodes542,544fully couple and below a threshold of the applied voltage, the electrodes542,544fully decouple.

In one embodiment, the electrostatic coupling of the electrodes542,544is in response to a signal or a sensed value from a sensor. In one embodiment, the power tool500, as shown inFIG.14, includes a sensor that is configured to detect flesh of the user at the blade592. In one embodiment, the sensor is a capacitive sensor. In one embodiment, the sensor is a conduction sensor. In one embodiment, the sensed value is conduction value and/or capacitance value for the purposes of detecting the difference between the user's flesh and wood/or other material of the workpiece on which the power tool500is being operated by the user. In one embodiment, the sensed value includes an accelerometer, indicating a rapid acceleration/rotation event (e.g., chainsaw kickback event, e.g., as disclosed in U.S. Pat. No. 7,552,781, which is incorporated by reference in its entirety). In one embodiment, in response to sensing the sensed value, the control circuit may cause a switch to actively engage working elements—e.g., brake may be actuated to stop a flywheel from rotating in a cordless nailer or a brake may be applied to a rotary mechanism in a rotary laser level.

In one embodiment, when the sensor (e.g., capacitive sensor or other sensors) detects flesh at the blade592, the electrostatically attractive clutch assembly518activates in response to the applied voltage and acts with full clamping force arresting the blade592and minimizing any user injury. In one embodiment, as shown inFIG.15, the electrostatically attractive plates542,544are opposing annular disks. In one embodiment, referring toFIGS.15-17, when the sensor (e.g., capacitive sensor or other sensors) detects flesh at the blade592, the electrostatic clutch assembly518is activated by the controller in response to the signal from the sensor. The electrodes542,544are then electrostatically attracted to each other. The electrostatic clutch assembly518, thus, acts with full clamping force arresting the blade592.

In one embodiment, as shown inFIGS.16-17, the electrodes542,544are combined with braking elements593that clamp on the blade592directly, either radially or axially. For example, as shown in the embodiment ofFIG.17, the electrodes542,544are combined with the braking elements593that clamp on the blade592radially, while, as shown in the embodiment ofFIG.16, the electrodes are combined with the braking elements593that clamp on the blade592axially.

In one embodiment, the saw braking system590has several advantages over the prior art saw braking execution described inFIG.1. For example, the saw braking system590of the present patent application is 1) quickly resettable, 2) not consumed, and 3) easily scales down to the size of handheld power tools—e.g., circular saw, reciprocating saw, etc. In one embodiment, the controller of the power saw, in response to the received signal from the sensor, is also configured to stop the rotation of the motor.

In one embodiment, the electrostatically attractive material is deposited on the axial (i.e., non-contact) faces of gears in a transmission, specifically a planetary transmission.

In one embodiment, the electrostatic clutch assembly518of the embodiments inFIGS.15-17remains fully energized and coupled until reset by the user. In one embodiment, the electrostatic clutch assembly518is reset with cycling of the trigger. In one embodiment, the saw braking system590with the electrostatic clutch assembly518is executed within a threshold volume.

Other applications of the electrostatic clutch/mechanism518of the present patent application include a quick release clamp or secure coupling of a battery to a power tool housing;. In one embodiment, the user is able to control the amount of slip or rotation, e.g., via a clutch dial, for controlling a speed of retraction of a tape measure.

In one embodiment, the motor, the motor and transmission assembly, the controller, the transmission, and the power source in the power tools200,300,400, and500may be similar to the motor15, the motor and transmission assembly14, the controller50, the transmission16, and the power source102, respectively as shown and described in other embodiments of the present patent application, and thus these will not be shown and described in detail here.