Patent Description:
This disclosure relates to linear actuators for use in automated machine tool systems, including robotic welding and other programmable tool applications. More generally, the disclosure relates to the thrust-bearing elements of a linear actuator system, including thrust tube and thrust rod components.

Industrial robots utilize a wide variety of different actuator technologies, in order to automate manufacturing processes including robotic welding, injection molding, fixture clamping, packaging, assembly, surface coating, and product inspection and testing. Other high-volume and precision production manufacturing applications are also included, particularly where machine tool speed, accuracy, endurance, service life and operational costs are important engineering factors.

In robotic welding and automated or programmable machine tool applications, actuators can be arranged to position a welding gun or similar apparatus with respect to a workpiece, using a linear actuator to position the electrode or end effector. Suitable applications include, but are not limited to, short-stroke clamping operations for arc, spot or resistance welding, projection welding, and friction stir welding. Linear actuators are also used in a range of other programmable tool applications, including robotic, pedestal, and fixture-type manufacturing operations.

Actuator speed, precision and service life remain important design factors across these different applications, along with system size and weight considerations. As a result, there is a continuing need for improved linear actuator designs, which can provide increased positioning accuracy with reduced deflection and tool displacement, within a desired tooling weight and size envelope, and a reasonable cost.

<CIT> relates to an actuator with a planetary roller screw (PWG) and describes a planetary roller nut carrier engaged within a first sleeve A, which sits nonrotating and axially fixed in a second sleeve B. The sleeve B extends radially outward of the roller nut carrier, and then axially along sleeve A, in which the roller nut carrier is disposed, to approximately the middle portion of the nut carrier and sleeve assembly.

According to the invention, the problem is solved by the subject matter outlined in independent apparatus claims <NUM> and <NUM> and independent method claim <NUM>. Advantageous further developments of the invention are set forth in the dependent claims.

In addition to the representative examples and embodiments described here, other embodiments are also encompassed, as disclosed by reference to the drawings, and by study of the following description.

Linear actuator systems can be provided in a variety of different sizes and configurations, depending on application, service, and operational requirements. Integrated-motor actuator systems provide a compact, efficient design, with the central housing section also serving as the stator housing. For example, a set of stator coils can be mounted to the inside the central housing section, with a rotor and screw shaft extending inside the stator, along the central axis. A nut assembly couples the rotor and screw shaft to a thrust tube or output rod, which moves longitudinally along the axis in response to rotation of the rotor.

Integrated motor actuators can be produced at relatively low cost with improved electromechanical efficiency and manufacturing advantages. Additional design benefits include high speed and positioning accuracy, with a reduced size envelope and improved power-to-weight ratio.

Weight can be an important design consideration in applications where the actuator device is typically carried by a robot, along with associated welding gun equipment or other machine tooling components. Less system weight also reduces loading on the robot arm, increasing speed and allowing for smaller robot systems with more precise positioning capability and higher rates.

The body portion of the actuator housing can be held together between end caps, for example using tie rods or similar mechanical fasteners. This design can also reduce weight, as compared to thicker-walled configurations, and improve the system's ability to cool the motor drive, which is also a consideration in applications requiring the device to perform at high repetition rates (e.g., more welds per minute), or with greater travel in each movement. Higher rates and greater travel distances both mean additional mechanical work output; that is, the motor drive needs to work harder, and the system thus generates more heat.

To address these concerns, the actuator configurations described here are adapted to accommodate a cooling assembly, for example an active water-cooled system or passive cooling structure. The addition of a cooling assembly can improve the motor capacity, for example up to two times or more, while maintaining acceptable system temperatures. In some embodiments the cooling assembly can be formed within the actuator housing, or otherwise permanently installed at the point of manufacture. In other embodiments, a modular cooling assembly can be adapted for selectively coupling (and decoupling) along one or more different sides or longitudinal section of the actuator housing.

Typical electric motor drives include an internal rotor, mounted with rotational bearings each end. The bearings are adapted to support the length of the rotor component in rotation about the longitudinal axis of the actuator, with precise clearance between the rotor and stator along the rotor length. In some configurations, the rotor can be supported by a single rotational bearing assembly at one end; e.g., at the proximal end, or between the proximal and distal ends. The rotor can also be provided in a short, standard or elongated configuration, with additional design features to reduce the mass and moment of inertia of the both the rotor and other components of the actuator drive.

Reference will now be made to the accompanying drawings, which assist in illustrating various features of the present disclosure. The following description is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the inventive aspects to the forms disclosed herein. Consequently, variations and modifications commensurate with the following teachings, skill, and knowledge of the relevant art are within the scope of the present inventive aspects.

<FIG> depicts a linear actuator system <NUM>, exemplary of the linear actuator systems discussed above and as described in greater detail below. The linear actuator system <NUM> is used to drive an output rod or thrust tube <NUM> in reciprocating motion along a longitudinal axis A.

In the configuration of <FIG>, thrust tube <NUM> is positioned at least partially within the main body or central portion of the actuator housing <NUM>. The thrust tube <NUM> extends along the longitudinal axis A from a first (proximal) end oriented toward the proximal end region 105a of the linear actuator system <NUM>, inside the housing <NUM>, to a second (distal) end 104b toward the distal end region 105b of the linear actuator system <NUM>, outside the housing <NUM>. In this particular example, the distal or output end 104b of the thrust tube <NUM> is positioned at the axial extreme of distal region 105b.

The distal end 104b of the thrust tube <NUM> can be coupled to a machine tool, workpiece, end effector, or other component. A motor assembly is positioned within the actuator housing <NUM>, and configured to drive the thrust tube <NUM> in reciprocating motion along the longitudinal axis A. The thrust tube <NUM> moves generally between a first (retracted) position to a second (extended) position, in which the distal end 104b of the thrust tube <NUM> advances at least partially outside of actuator housing <NUM> and past the head assembly <NUM>. This reciprocating motion between the first retracted position and the second extended position can be used to drive a machine tool in a corresponding fashion along the longitudinal axis A.

As used herein, the terms "proximal" and "distal" are defined with respect to the internal components of the linear actuator system <NUM>, and any workpiece or tool coupling located on the output end 104b of the thrust tube <NUM>, outside of the actuator housing <NUM>. In particular, the term distal refers to the direction of the output end 104b of the thrust tube <NUM> that is at least partially outside of the housing <NUM> (and any workpiece or tooling component connected thereto), and the term proximal refers to the direction away from the output end 104b of the thrust tube <NUM> (and any connected workpiece or tool). Alternatively, the terms may be interchanged without loss of generality, depending on design or drawing convention.

The actuator housing <NUM> shown in <FIG> generally encloses a portion of the thrust tube <NUM>. The actuator housing <NUM> further encloses a motor assembly and any other appropriate components that are used to drive the reciprocating motion of the thrust tube <NUM>. Exemplary internal components are described in greater detail with respect to <FIG>, including a motor assembly (e.g., magnets, windings, and rotors), bushings, bearings, and a nut assembly coupled to a lead screw or screw shaft for converting rotational motion of the rotor into reciprocating motion of the thrust tube <NUM> along central axis A.

The main or central portion of the actuator housing <NUM> can be formed by extruding or machining a generally hollow shape configured to enclose the motor assembly and other internal components, or as a multi-piece assembly. More generally, the actuator housing can encompass the main or central housing section <NUM> together with a head assembly <NUM>, bearing block <NUM> and rear cover <NUM>, attached together along the central axis A. As shown in <FIG>, for example, the head assembly <NUM> is coupled to the distal end of the main housing <NUM> along the longitudinal axis A, in the distal region 105b of the actuator system <NUM>, and the main bearing block <NUM> and rear cover <NUM> are coupled to central portion of the housing <NUM> in the proximal region 105a.

As described herein, the linear actuator system <NUM> converts rotational motion (e.g., of an internal screw) into reciprocating motion of the thrust tube <NUM>. The main bearing block <NUM> can enclose various components adapted for precision control of the reciprocating motion, such as a rotary encoder that detects a rotational position of the internal screw and other control components or logic that uses the detected position to determine a reciprocated position of the thrust tube <NUM>. Bearing block connectors <NUM> can be used to removably attach the main bearing block <NUM> to the actuator housing <NUM>. In this configuration, the main bearing block <NUM> can be interchangeable, allowing the linear actuator to be used with a variety of different encoders, sensors, feedback mechanisms, and so on, as appropriate for a given application. As described herein, an adapter is provided to connect the screw shaft and other internal components of the actuator to be associated with different bearing blocks, including those having different sizes or configurations than the main bearing block <NUM> shown with respect to <FIG>.

External connectors 115a, 115b are positioned at or on the main bearing block <NUM>. The connectors 115a, 115b are used to connect the linear actuator system <NUM> to various external systems and processes. For example, the connectors 115a, 115b can be used to electrically connect the linear actuator system <NUM> to a power source. Additionally or alternatively, the connectors 115a, 115b can be used to provide a data connection between the linear actuator system <NUM> and an external computing device, which may be adapted to control one or more operations of the linear actuator system <NUM>.

Connectors 115a, 115b are illustrative. Connectors 115a, 115b can be used to provide connections or links between the linear actuator system <NUM> and an external power supply, computing device, and other peripheral systems, or other connections can be used. As one example, a remote computing device may be wirelessly coupled with one or more internal components of the linear actuator system <NUM>. As such, control signals and data outputs can be exchanged between the remote computing device and the linear actuator system <NUM> by wireless connection, according to various protocols.

The main bearing block <NUM> is shown connected to a rear cover <NUM>. The rear cover <NUM> can be a plate or other closure that operates to close and seal an interior of the main bearing block <NUM> from an external environment. The rear cover <NUM> can also provide access to service or replace various components that are held within the main bearing block <NUM>. As one example, the main bearing block <NUM> may include various sensors and other electronics that may be shielded by the rear cover <NUM>. As shown in <FIG>, rear cover connectors <NUM> such as bolts, screws or other mechanical connectors can be used to secure to rear cover <NUM> to the main bearing block <NUM>. The rear cover connectors <NUM> can be manipulated in order to remove the rear cover <NUM> from the main bearing block <NUM> and allow for servicing of the components held therein.

A front head assembly <NUM> is removably attached to the actuator housing <NUM> at the distal end region 105b, for example using screws, bolts or similar front head connectors <NUM>. As described herein, the front head assembly <NUM> houses an adjustable guide bushing that can provide stability to the thrust tube <NUM>, as the thrust tube <NUM> travels in reciprocating motion along the longitudinal axis A. The front head assembly <NUM> in cooperation with the adjustable guide bushing <NUM> can also provide rotational stability to the thrust tube <NUM>. As one example, the thrust tube <NUM> can define a flat <NUM> or other surface contour. The front head assembly <NUM> can include one or more features, include the adjustable guide bushing, with a correspondingly contoured feature that is key to the flat <NUM>, thereby helping the thrust tube <NUM> maintain rotational stability as the thrust tube <NUM> travels along longitudinal axis A.

The linear actuator system <NUM> described herein also includes various cooling features, systems and assemblies that help reduce a temperature of the motor assembly contained within the actuator housing <NUM>. In the example of <FIG>, the linear actuator system <NUM> is shown as including a cooling loop <NUM>. The cooling loop <NUM> can be at least partially embedded, potted or seated with a thermally conductive material <NUM>, within a channel or recessed feature <NUM> defined in the actuator housing <NUM>. The cooling loop <NUM> can be formed with the thermally conductive material <NUM> disposed at least partially about the cooling loop <NUM> to conduct heat from the actuator housing <NUM>. The cooling loop <NUM> can include a hollow interior conduit or tube through which cooling fluid is routed. A first fluid coupling 122a and a second fluid coupling 122b can be used to couple the cooling loop <NUM> with a fluid source for circulating the cooling fluid. In some cases, the fluid couplings 122a, 122b can include inlet and outlet couplings, valves or quick-disconnect features adapted for removable attachment of the cooling loop <NUM> to conduit, hose or other fluid flow component configured to cycle fluid through the cooling loop <NUM>.

The recessed feature <NUM> is shown formed in a first side 109a of the actuator housing <NUM>. The cooling loop <NUM> is therefore at least partially embedded, potted or seated at the first side 109a of the actuator housing <NUM>. The cooling loop <NUM> in the example of <FIG> conducts heat substantially from the first side 109a. A second side 109b, or other side of the actuator housing <NUM>, remains substantially uncoupled from the cooling loop <NUM>. It will be appreciated, however, that in other cases, multiple cooling loops can be provided, with corresponding recessed features formed in to each respective side, or all sides, of the actuator housing <NUM> as needed. Yet further, in other cases, the second side 109b or other side of the actuator housing <NUM> may be adapted to receive another cooling component, such as a modular cooling jacket or other cooling jacket that attaches to a side of the actuator housing <NUM> that is otherwise not associated with the cooling loop <NUM> shown in <FIG>. In this configuration, the linear actuator system <NUM> can be tuned to provide the level of cooling as needed for a particular application.

<FIG> is a cross-sectional view of the actuator system <NUM>. In this particular configuration, linear actuator system <NUM> includes a motor assembly <NUM> disposed within the central portion of the actuator housing <NUM>. A head assembly <NUM> is coupled to the central housing <NUM> in the distal end region 105b, e.g., using one or more front head connectors <NUM>, or similar mechanical attachments. A bearing block <NUM> and rear cover <NUM> are connected to the central housing <NUM> at the proximal end 105a, opposite the head assembly <NUM>, for example using one or more bearing block connectors <NUM> and rear cover connectors <NUM>. Motor assembly <NUM> is located inside the central housing <NUM>.

Motor assembly <NUM> typically includes a stator with a number of motor windings <NUM>, magnets <NUM> (e.g., permanent magnets or electromagnets), and a rotor <NUM>. For example, motor assembly <NUM> may be configured as a hollow shaft motor having one or more stationary (stator) motor windings <NUM>, with a centrally located, hollow rotor <NUM> positioned radially inwardly of stator windings <NUM>, inside actuator housing <NUM>. Conversely, windings <NUM> are positioned radially outwardly of rotor <NUM>, for example, being fixed to (or fixed relative to) actuator housing <NUM>.

When motor assembly <NUM> is provided in hollow shaft or hollow rotor form, as shown in <FIG>, rotor <NUM> may have generally cylindrical outer and inner surfaces, with stator windings <NUM> and rotor <NUM> surrounding a centrally located linear thrust mechanism that includes a threaded lead screw or screw shaft <NUM>, with nut (or nut assembly) <NUM> directly coupled to the thrust tube, output rod, or other load transfer structure.

The thrust mechanism is configured to convert rotational motion of rotor <NUM> to linear movement of thrust tube <NUM>. As shown in <FIG>, for example, the thrust mechanism includes the externally threaded, elongated lead screw or screw shaft <NUM> in combination with an internally threaded nut assembly <NUM>, positioned radially inward of and substantially surrounded by rotor <NUM>. In this configuration, screw shaft <NUM> may include an externally threaded section, provided with threads along a substantial portion of the shaft length. As used herein, the terms "thread" and "threaded" may thus be used to define the main threaded section of screw shaft <NUM>, including, but not limited to, conventional threads, Acme- or ACME-type threads, roller screw threads, ball nut threads, and other threaded features suitable to convert rotational motion of rotor <NUM> to linear motion of thrust tube <NUM>.

Depending on design, the lead screw or screw shaft <NUM> may also include a proximal extension <NUM>. Proximal extension <NUM> may be formed as an unthreaded, reduced diameter section at the proximal end of screw shaft <NUM>. The proximal extension <NUM> extends through hub <NUM> and may be rotationally coupled thereto, for example, by providing the inner surface of hub <NUM> with a complementary taper, or with a lock and key arrangement.

Thrust bearing <NUM> can be positioned radially outward of hub <NUM> and configured to support hub <NUM> and the proximal extension <NUM> of screw shaft <NUM> within actuator housing <NUM>. In some examples, the thrust bearing <NUM> can include a pair of bearings that are adapted to provide a higher force capacity. Accordingly, while <FIG> shows the thrust bearing <NUM> as a single bearing, two or more bearings can be provided at or adjacent the proximal end to support screw shaft <NUM> within the housing <NUM>. Depending upon design, rotor <NUM> and hub <NUM> may be provided as a single, integrated component, or as separate parts. The proximal end of rotor <NUM> can also be rigidly connected with the axially extending (rotor mounting portion) of hub <NUM>, so that rotation of rotor <NUM> causes a corresponding rotation of hub <NUM> and lead screw (or screw shaft) <NUM>.

A feedback device or block <NUM>, for example including an optional braking assembly, can also be arranged adjacent the proximal extension <NUM> of the screw shaft <NUM>, with a mounting plate <NUM> facilitating attachment within the main bearing block <NUM>. A rotary encoder <NUM> or other position sensor/controller may be mounted to the proximal extension <NUM> of screw shaft <NUM>, utilizing an adapter <NUM>. For example, a hollow shaft (incremental or absolute) encoder <NUM> can be coupled to the adapter <NUM> using a threaded connection or other mechanical means, with the rotation sensor element mounted directly onto the adapter <NUM>. In turn, the adapter <NUM> can also be coupled to the screw shaft <NUM> in a manner that causes the adapter <NUM> to rotate with the rotation of the screw shaft <NUM>. Accordingly, while the adapter <NUM> is shown in <FIG> for use with a hollow bore feedback device, other configurations are possible and contemplated herein. For example, feedback devices that do not require a hollow bore connection can be implemented, including those in which a direct coupling of device and adapter <NUM> and/or screw shaft <NUM> is utilized (e.g., such an Oldham coupler, threaded coupling, or other mechanical engagement).

In the example of <FIG>, the screw shaft <NUM> includes a coupling feature or fitting <NUM> at a proximal end of the screw shaft <NUM>. While many configurations are possible, the coupling feature <NUM> defines a proximal fitting <NUM> or socket that is adapted to receive the adapter <NUM>. The adapter <NUM> can define an adapter fitting <NUM> that is a reduced diameter portion of the adapter <NUM>. The adapter fitting <NUM> can be inserted into the proximal fitting <NUM> of the screw shaft <NUM>. In some cases, the adapter fitting <NUM> and the proximal fitting <NUM> can define a press fit or interference fitting, or a threaded coupling. A lock nut <NUM> can also be provide to restrain the rotational and axial movement of the adapter <NUM> and the screw shaft <NUM> relative to one another.

A load distribution washer <NUM> is shown in <FIG> with the proximal extension <NUM> and the coupling feature <NUM> extending therethrough. The load distribution washer <NUM> can further enhance the stability of the screw shaft <NUM> during operation. The load distribution washer <NUM> can be pressed between the lock nut <NUM> and the thrust bearing <NUM> / hub <NUM> along the longitudinal axis A, thereby providing a more evenly distributed load along the longitudinal axis A-A for the components configured for rotational motion thereabout.

The distal end of thrust tube <NUM> may be adapted for association with an adjustable guide bushing <NUM> that supports and stabilizes the distal end of the thrust tube <NUM> relative to actuator housing <NUM>. For example, the adjustable guide bushing <NUM> may be generally arranged at the distal end 105b of the system <NUM>. At the distal end 105b, the adjustable guide bushing <NUM> may be configured to provide axial and rotational stability to the thrust tube <NUM> as the thrust tube <NUM> reciprocates along the longitudinal axis A between a retracted and an extended state, as explained in detail with respect to <FIG>. This can involve keying one or more contours of the adjustable guide bushing <NUM> to a corresponding contour of the thrust tube <NUM> (e.g., the flat <NUM> of <FIG>).

In some embodiments, the distal end of rotor <NUM> may be provided with a ledge, recessed portion, or other feature to accommodate a secondary bearing <NUM> configured to support and stabilize the distal end of the rotor <NUM> relative to actuator housing <NUM>. As one possibility, a secondary bearing <NUM> may be provided, which may be adapted to float or travel in an axial direction (parallel to rotational axis A of rotor <NUM> and lead screw <NUM>), in order to accommodate thermal expansion of rotor <NUM> and other components.

The central portion of rotor <NUM> can be provided with a number of magnets <NUM>, mounted either along the outer surface of rotor <NUM>, or inlaid within the outer surface of rotor <NUM>, adjacent the stator windings or coils <NUM>. For example, rotor <NUM> can be machined to form axially-extending channels or grooves along the central portion of rotor <NUM>, and magnets <NUM> can be inlaid within the grooves, between the corresponding (and radially thicker) axial rib sections. This also may provide rotor <NUM> with thicker wall sections at the proximal and distal ends, extending axially on either side of magnets <NUM>.

An axial channel and rib structure reduces the mass and movement of inertia of rotor <NUM>, so that less torque is required for angular acceleration and deceleration. The outer (proximal and distal) ends of rotor <NUM> can also be provided with a plurality of slots, holes or apertures extending through the wall sections, in order to further reduce inertia and torque requirements. Rotor <NUM> also provides for simple assembly of the motor <NUM>, without additional tooling for alignment, while providing sufficient material to reduce or limit core saturation due to the high flux density of magnets <NUM>, and reducing stray flux and flux leakage.

When motor assembly <NUM> is operated, rotor <NUM> rotates in a first (e.g., clockwise) or second (e.g., counter-clockwise) direction about longitudinal axis A. The proximal end of rotor <NUM> is connected to screw shaft <NUM> (e.g., via hub <NUM>), so that rotation of rotor <NUM> results in a corresponding rotation of screw shaft <NUM>, in either the first or second direction.

The nut assembly <NUM> may include internal threads, for example a recirculating ball screw or roller nut <NUM> which mates with external threads on the outer surface of screw shaft <NUM> to convert rotational motion of rotor <NUM> to linear (axial) motion of nut assembly <NUM>. The nut assembly <NUM> and thrust tube <NUM> are directly coupled together, and thus move in unison along the longitudinal axis A when screw shaft <NUM> is rotated by rotor <NUM> of motor assembly <NUM>.

The nut assembly <NUM> and the thrust tube <NUM> can be directly coupled to one another, absent additional intervening housing or bearing structures, providing linear actuator system <NUM> with a more compact design. Further, without additional housing or bearing structures, the screw shaft <NUM> can be oversized or generally larger than conventional designs relative to the dimensions of the actuator housing <NUM>. In this manner, the actuator system <NUM> can provide enhanced torque relative to the size of the system <NUM>, while using the cooling systems described herein to remove heat and maintain a temperature of the system <NUM>.

In the example of <FIG>, the nut assembly <NUM> includes a first end 161a adjacent the hub <NUM> and a second end 161b adjacent the thrust tube <NUM>. The second end 161b directly abuts the thrust tube <NUM>, for example at a mechanical coupling or fitting <NUM>. A complementary fitting <NUM> is defined on the second end 161b of the nut assembly <NUM>, for example a threaded coupling, press fit or interference fitting adapted for engagement with the fitting <NUM> on the proximal end 104a of the thrust tube <NUM>. In this configuration, the thrust tube <NUM> can be directly coupled with the roller nut <NUM> or nut assembly <NUM>, absent additional housing or load bearing structures between the mechanical coupling <NUM> on the second end 161b of the nut assembly <NUM> and the complementary fitting <NUM> on the proximal and of the thrust tube <NUM>.

As shown in <FIG>, the roller nut <NUM> is held within the nut assembly <NUM> by a carrier <NUM> that extends between the first and second ends 161a, 161b. In the example of <FIG>, the carrier <NUM> defines the mechanical coupling <NUM> at the second end 161b of the nut assembly <NUM>. End caps 164a, 164b can be provided at the respective first and second ends 161a, 161b, for structural support and to mitigate debris entry into roller nut <NUM>. In some cases, the end caps 164a, 164b can define the mechanical coupling <NUM>, alone or in conjunction with the carrier <NUM>.

For example, nut assembly <NUM> and thrust tube <NUM> may move in a distal direction in response to a first (clockwise) rotation of rotor <NUM> and the lead screw or screw shaft <NUM>, the output end of the thrust tube <NUM> away from the actuator housing <NUM> along axis A of the linear actuator system <NUM>. Conversely, when motor assembly <NUM> drives rotor <NUM> and screw shaft <NUM> in the opposite (counter-clockwise) direction, nut assembly <NUM> and thrust tube <NUM> move in a proximal direction along the longitudinal axis A, retracting the thrust tube <NUM> into the actuator housing <NUM>. For example, the thrust tube <NUM> can be retracted into an inner volume <NUM> of the actuator housing <NUM>. A bumper <NUM> may be provided between the thrust tube <NUM> and the screw shaft <NUM> or other component of the system <NUM>. The bumper <NUM> defines a deformable interface region between inner surface of the thrust tube <NUM> at working or output (distal) end, and the adjacent end of the screw shaft <NUM>, cushioning impact and reducing contact forces at the inward-most position of thrust tube <NUM>.

Alternatively, the threading configuration may be different, and the proximal and distal motions of thrust tube <NUM> may be reversed with respect to the rotation of screw shaft <NUM>. Thus, motor assembly <NUM> is controllable to provide any desired linear or axial motion of thrust tube <NUM>, and any workpiece or tooling connected thereto, based on the rotational motion of rotor <NUM> and screw shaft <NUM>.

<FIG> is a cross-sectional view of the nut assembly <NUM> and thrust tube <NUM>, directly coupled to one another. The nut assembly <NUM> is shown directly engaged with a proximal end of the thrust tube <NUM>. For example, the nut assembly <NUM> can extend continuously from the first end 161a to the second end 161b, with the second end 161b abutting the thrust tube <NUM>. The nut assembly <NUM> and the thrust tube <NUM> can thus be directly coupled to one another, absent additional housing or bearing structure intervening between the nut assembly and the proximal end of the thrust tube.

As shown in <FIG>, the mechanical coupling <NUM> can include a threaded coupling, press fit or interference fitting on the second end 161b of the nut assembly <NUM>. The mechanical coupling <NUM> can be adapted to engage a complementary fitting or coupling <NUM> on the proximal end 104a of the thrust tube <NUM>, opposite the distal and 104b, within a common outer diameter of the thrust tube <NUM> and nut assembly <NUM>. For example, the nut assembly <NUM> may define a nut assembly outer surface <NUM> and the thrust tube <NUM> can define a thrust tube outer surface <NUM>. The nut assembly outer surface <NUM> and the thrust tube outer surface <NUM> can be substantially continuous with one another, each having a common or similar outer diameter.

In this configuration, the directly coupled nut assembly <NUM> and the thrust tube <NUM> can be arranged within the rotor <NUM>, with the rotor <NUM> adapted to accommodate and match the common outer diameter, with a desired tolerance, rather than being sized larger for additional intervening housing or bearing structures. In turn, the nut assembly <NUM> and the directly coupled thrust tube <NUM> can be configured to house an oversized or larger lead screw or screw shaft <NUM>, facilitating the compact designs described herein with the enhanced torque due to the larger screw shaft <NUM> fitting in a more compact space.

In <FIG>, the output (distal) end 104b of the thrust tube <NUM> is shown with a mechanical coupling or similar attachment fixture on the rod end <NUM>. The rod end or attachment fixture <NUM> can be configured as threaded coupling or similar fixture for a machine tool component, located on the output (distal) end 104b of the thrust tube <NUM>, outside the actuator housing <NUM>. For example, an effector for a weld gun or other machine tool component can be coupled to the rod end <NUM>, and driven in axial motion by the thrust rod <NUM>.

The rod end (or fixture) <NUM> is typically positioned by thrust tube <NUM> at or adjacent the distal end 105b of the linear actuator system <NUM>. The rod end <NUM> defines a common interface that allows the thrust tube <NUM> (and more generally, the linear actuator system <NUM>) to engage a variety of different effectors and other machine tool components. The rod end <NUM> can also include a variety of engagement features, including pins, clamps, screws, grooves, locking mechanisms, and so forth, which are used to secure the effector or machine tool component to the thrust tube <NUM>. For example, a weld electrode or similar machine tool component can be directly coupled or secured to the rod end <NUM>, and move with the reciprocating motion of the thrust tube <NUM>. Alternatively, an end effector or other load bearing component can be coupled to the rod end <NUM> in order to manipulate the machine tool, for example a welding gun arm.

Adjacent the tool attachment, a grease zerk or similar fitting <NUM> is provided on the distal end of the thrust tube <NUM>, positioned at the distal end 105b of the actuator system <NUM>. The grease zerk <NUM> can be used to receive a supply of lubricant for the inner volume <NUM>. A seal <NUM>, such as an O-ring can be mounted at the distal (output end) of the thrust tube <NUM>, mitigating lubricant leakage.

<FIG> is an exploded view of the thrust tube <NUM> and the front head assembly <NUM>. The front head assembly <NUM> generally closes the distal end 105b of the actuator housing <NUM> and helps provide stability to the thrust tube <NUM>. For example, the front head assembly <NUM> include various components that cooperate to receive the thrust tube <NUM> and guide the reciprocal movement of the thrust tube <NUM>, including the adjustable guide bushing <NUM>, the thrust tube wiper <NUM> and the thrust tube scraper <NUM>, as shown in <FIG>.

In one example, the thrust tube <NUM> can include one or more surface contours that are keyed to corresponding features of the front head assembly <NUM> for reciprocal movement there along. In <FIG>, the thrust tube <NUM> is shown with a first flat 106a and a second flat 106b. The first and second flats 106a, 106b can be positioned on opposing sides of the thrust tube <NUM> and define a substantially flat or planar contour along the longitudinal dimension of the thrust tube <NUM>. In other examples, the thrust tube <NUM> can include more or fewer flats, including flats in different positions and configurations.

The flats 106a, 106b can be keyed or matched to corresponding contours of the front head assembly <NUM>. In this configuration, the front head assembly <NUM> can receive the thrust tube <NUM>, and the flats 106a, 106b can mitigate rotational movement of the thrust tube <NUM> as the thrust tube reciprocates along the longitudinal axis. For example, the adjustable guide bushing <NUM> can provide a first bushing portion 132a and a second bushing portion 132b that receive the thrust tube <NUM> within the front head assembly <NUM>. The first bushing portion 132a can define a first keyed contour 134a and the second bushing portion 132b can define a second keyed contour 134b. The adjustable guide bushing <NUM> can be adapted to receive the thrust tube <NUM> with the flat 106a engaged with the first keyed contour 134a and the flat 106b engaged with the second keyed contour 134b. As the thrust tube <NUM> reciprocates through the adjustable guide bushing <NUM>, the keyed contours 134a, 134b thus impair rotational movement of the thrust tube <NUM>, due to the engagement with the respective ones of the flats 106a, 106b. Pins <NUM> are provided to install the adjustable guide bushing <NUM> in the system <NUM>.

As shown in <FIG>, the flats 106a, 106b can be further keyed to contours of the front head assembly <NUM>, such as the first front head contour 131a and the second front head contour 131b. Similarly, the thrust tube wiper <NUM> can include a first wiper engagement contour 137a, second wiper engagement contour 137b for engagement with the first and second flats 106a and 106b. The thrust tube scraper <NUM> is also shown the first scraper engagement contour 139a and the second scraper engagement contour 139b for engagement with the first and second flats 106a, 106b.

<FIG> is an exploded view of linear actuator system <NUM>, including a motor assembly <NUM>, lead screw or screw shaft <NUM> and nut assembly <NUM> directly coupled to the thrust tube <NUM>. As shown in <FIG>, the directly coupled nut assembly <NUM> and thrust tube <NUM> are adapted to receive the screw shaft <NUM>, with the nut assembly <NUM> engaged with the external outer threads of the screw shaft <NUM>. The rotor <NUM> extends along and over the directly coupled nut assembly <NUM> and thrust tube <NUM> so that the nut assembly <NUM> and the thrust tube <NUM> fit in an annular space between the screw shaft <NUM> and the rotor <NUM>.

The rotor <NUM> is positioned within the actuator housing <NUM>, adjacent the cooling loop <NUM>. The cooling loop <NUM> is therefore arranged to remove heat from the motor assembly <NUM> through the actuator housing <NUM>. The adapter <NUM> is shown in <FIG> as connected to the screw shaft <NUM>. The adapter <NUM> generally operates to couple the screw shaft <NUM> to the encoder <NUM> of the main bearing block <NUM>. The adapter <NUM> can have an appropriate length in order to extend from the screw shaft <NUM> to the encoder <NUM>. In this manner, the screw shaft <NUM> and actuator system <NUM> can be manufactured separately from the encoder <NUM> and main bearing block <NUM>, with the adapter <NUM> tuned to effectively extend a length of the screw <NUM> to meet the specific characteristics of the encoder <NUM>. As an illustration, different types or configurations of encoders may have different sizes. The actuator system <NUM> can include a common sized screw shaft <NUM> and the adapter <NUM> can be any one of a variety of different sizes to connect the commonly sized screw shaft <NUM> to the specific encoder of a given application.

<FIG> is a cross-sectional view of the lead screw or screw shaft <NUM> and adapter <NUM>. The screw shaft <NUM> can have a shaft length ls and the adapter <NUM> can have an adapter length la. Generally, the shaft length ls can be a length value that is standardized across a series or particular model of actuator system <NUM>. The adapter <NUM> can have an adapter length la that is tailored to the requirements of the encoder <NUM>.

<FIG> is an exploded view of the main bearing block <NUM> assembly for a linear actuator system <NUM>. As shown in <FIG> and as described above, the main bearing block <NUM> can be associated with or otherwise include the connectors 115a, 115b, the rear cover <NUM>, the thrust bearing <NUM>, the distribution washer <NUM>, the lock nut <NUM>, the feedback device or feedback block <NUM>, the rotary encoder <NUM> and the mounting plate <NUM>. In some cases, an alternate feedback block <NUM>' can be substituted for the feedback block <NUM>. Suitable feedback blocks <NUM>' can include an integrated pilot feature with braking assembly. In this configuration, the braking assembly is configured to brake rotation of the screw shaft responsive to feedback from the resolver or encoder. Other variations of the feedback block <NUM> or <NUM>' may be provided, and are encompassed in the disclosure here.

<FIG> is a top view of the linear actuator system <NUM>. In the top view, the cooling loop <NUM> is shown coupled with the actuator housing <NUM>. For example, the actuator housing <NUM> can define the recessed feature <NUM> with the first side of the actuator housing <NUM>. The recessed feature <NUM> can be sized and shaped in a manner so that the cooling loop <NUM> can be at least partially embedded, potted or seated within the actuator housing <NUM>, along the selected side. In the example of <FIG>, the cooling loop <NUM> extends along the recessed feature <NUM> from the first fluid coupling 122a near the proximal end <NUM> a of the actuator housing <NUM> toward the distal end 105b of the actuator housing <NUM> and back to second fluid coupling 122b near the proximal end 105a. In this manner, the cooling loop <NUM> can resemble a U-shaped conduit. In other examples, the cooling loop <NUM> can be defined by other geometries, including geometries in which the cooling loop <NUM> extends the actuator housing <NUM> multiple times, such as extending in a serpentine pattern between the near the proximal and distal ends 105a, 105b, similar to a radiator or other cooling structure.

<FIG> is a front view of the actuator system <NUM>, showing an anti-rotation feature for the thrust tube <NUM>. As illustrated in the front view, the thrust tube <NUM> can include flats 106a, 106b on opposing sides. The front head assembly <NUM> can include one or more components that are keyed to the flats 106a, 106b. For example and as described above, the front head assembly <NUM> can housing a guide bushing and other features that have contours matching those of the flats 106a, 106b. In this manner, as the thrust tube <NUM> reciprocates, the thrust tube <NUM> may be prevented from rotational movement.

<FIG> is a back view of the actuator system <NUM>. In the back view, the connectors 115a, 115b are shown. The connectors 115a, 115b can be adapted for power and control communications. For example, one or both of the first connector 115a and the second connector 115b can be used to connect the linear actuator system <NUM> to a power supply, remote computing unit, and other external system or process. Each of the first connector 115a and the second connector 115b can be configured to connect the linear actuator system <NUM> to distinct systems. For example, the first connector 115a may be configured to connect the linear actuator system <NUM> to a power supply and the second connector 115b may be configured to connect the linear actuator system <NUM> to a remote computing unit. In other cases, more or fewer connectors may be provided, as may be appropriate for a given application.

<FIG> is a flow diagram illustrating a process or method <NUM> for operating a linear actuator system. For example, process <NUM> may be used with a linear actuator system <NUM>, in any of the examples and embodiments described herein. While the specific operations of method <NUM> are presented in a particular arrangement, method <NUM> may include more, fewer or different steps than those that are illustrated, consistent with the teachings of this disclosure. The operations of method <NUM> can also be performed in any order or combination, with or without any of the additional processes and techniques described herein.

At operation <NUM>, the motor of the linear actuator is operated. The motor has a stator and a rotor disposed about a screw shaft of a linear actuator. The rotor rotates about a longitudinal axis. For example and with reference to <FIG>, the motor assembly <NUM> of the linear actuator system <NUM> is operated. The stator windings or coils <NUM> and the rotor <NUM> are disposed about the lead screw or screw shaft <NUM>. The rotor <NUM> rotates about the longitudinal axis A-A.

At operation <NUM>, a thrust tube is driven along the longitudinal axis. The thrust tube is directly coupled to a nut assembly in threaded engagement with the screw shaft. For example and with reference to <FIG>, the thrust tube <NUM> is driven in reciprocating movement along the longitudinal axis A-A. The thrust tube <NUM> is directly coupled to the nut assembly <NUM>. In one example, directly coupling the thrust tube <NUM> and the nut assembly <NUM> can include a direct physical engagement between the nut assembly <NUM> and the proximal end of the thrust tube <NUM>, absent additional housing or bearing structures intervening there between. The nut assembly <NUM> is in threaded engagement with the screw shaft <NUM>.

At operation <NUM>, the thrust tube is loaded. The thrust tube extends from a proximal end in direct physical engagement with the nut assembly to a distal end subject to the loading. For example and with reference to <FIG> and <FIG>, the thrust tube <NUM> can be loaded at the rod end or attachment fixture <NUM>. In one example, the rod end <NUM> can be coupled with a weld electrode or weld gun effector for use in resistance welding operations.

There may be substantial mechanical loading on the weld electrodes in order to provide the mechanical coupling required to ensure high quality welds. The greater the axial mechanical loading and radial (inductive) loading due to the weld current, the greater the potential for displacement of the rod end <NUM> and associated weld electrode. The inductive reaction forces can cause the welding gun and actuator assembly to deflect off axis, causing the electrodes to slip or skid out of the desired position and potentially impacting weld quality.

At operation <NUM>, rotational stability is provided to the thrust tube. The thrust tube is supported with a bushing or bearing proximate the distal end. For example and with reference to <FIG> and <FIG>, the adjustable guide bushing <NUM> supports the thrust tube <NUM>. The adjustable guide bushing <NUM> includes the keyed contours 134a, 134b that are adapted for engagement with corresponding ones of the flats 106a, 106b of the thrust tube <NUM>. As the thrust tube <NUM> reciprocates along the longitudinal axis A-A, the adjustable guide bushing <NUM> can therefore mitigate rotational movement of the thrust tube <NUM>, with the first and second bushing portions 132a, 132b preventing rotational movement of the thrust tube <NUM>.

At operation <NUM>, heat is dissipated with a cooling loop. For example, and with reference to <FIG> and <FIG>, the cooling loop <NUM> can be partially embedded, potted or seated within the actuator housing <NUM>. In some cases, the actuator housing <NUM> can define a recessed feature <NUM> with the cooling loop <NUM> positioned at least partially therein. The cooling loop <NUM> extends along the actuator housing <NUM> and along the stator and rotor disposed about the screw shaft. A thermally conductive material <NUM> can be at least partially disposed about the cooling loop <NUM> conducting the heat from the housing to the cooling loop <NUM>.

Systems devices and techniques related to linear actuators are disclosed herein. A linear actuator generally includes a thrust tube configured for reciprocating motion along a longitudinal axis. A distal end of the thrust tube is configured to engage a machine tool, such as a welding, crimping, clamping, or other tool, thereby allowing the linear actuator to drive the machine tool in reciprocating motion with the thrust tube. The linear actuator can be used in an automated assembly or manufacturing and other settings where the distal end of the thrust tube is subject to loading, including both axial (e.g., mechanical) loading and transverse or radial (e.g., mechanical or current-based inductive) loading, which generates forces tending to displace the thrust tube at the distal end.

As described herein, a nut assembly directly couples a rotor and screw shaft to the thrust tube to provide a compact, efficient design. Additionally, the actuator configurations described herein have the ability to accept a modular water cooling assembly, or other active or passive modular cooling unit. The addition of the cooling assembly adds to the motor capacity, allowing the actuator to operation with a higher-capacity, while maintaining acceptable system temperatures.

Claim 1:
A linear actuator system (<NUM>) comprising:
an actuator housing (<NUM>) extending along a longitudinal axis (A);
a motor assembly (<NUM>) including a stator (<NUM>) coupled to an inner surface of the actuator housing (<NUM>) and a rotor (<NUM>) extending within the actuator housing (<NUM>);
a screw shaft (<NUM>) extending within the rotor (<NUM>), along the longitudinal axis (A);
a nut assembly (<NUM>) engaged with the screw shaft (<NUM>); and
a thrust tube (<NUM>) extending from a proximal end (104a) directly coupled with the nut assembly (<NUM>) to a distal end (104b) disposed at least partially outside the housing (<NUM>);
wherein the nut assembly (<NUM>) is configured to convert rotational motion of the rotor (<NUM>) about the longitudinal axis (A) to linear motion of the thrust tube (<NUM>) along the longitudinal axis (A); and
wherein the rotor (<NUM>) is disposed about the screw shaft (<NUM>) and nut assembly (<NUM>), with the thrust tube (<NUM>) disposed radially inward of an annular region defined between an outer diameter of the nut assembly (<NUM>) and an inner surface of the rotor;
characterized in that the nut assembly (<NUM>) extends continuously from a first end (161a) opposite the thrust tube (<NUM>) to a second end (161b) abutting the thrust tube (<NUM>), and further comprising a mechanical coupling (<NUM>) defined on the second end (161b), in direct physical engagement with the proximal end (104a) of the thrust tube (<NUM>).