Patent Description:
Power tools, and in particular random orbital sanders are used by a variety of professionals to perform sanding functions for their craft. Operation of sanding tools often causes vibrations. <CIT> discloses a a robotic paint repair system comprising a compliant accessory actuator capable of applying a desired force and a desired stiffness to the consumable abrasive product in response to sensed data collected between the tool and the substrate. <CIT> and <CIT> disclose the use of rheological materials for dampening.

According to the present invention, a sanding system is defined according to independent claim <NUM>, and a method of mechanically sanding a surface according to independent claim <NUM>.

Many sanding and repair operations are increasingly being done by robotic repair units. One of the last areas to be automated includes sanding and polishing operations, which often benefit from an experienced user applying pressure at a desired amount to achieve the desired finish.

One particular area where robots are lacking behind their human counterparts is adaptability of changing pressure when sanding over non-flat part features. Generally, this is handled today by using compliant abrasive products (such as abrasive nonwoven wheels or bristle products) that 'give' when unit pressure increases over the radius or edge of a part. This prevents changing part dimensions but at the expense of cut rate and abrasive selection. By moving the compliance mechanism into the abrasive tool itself, it could allow for any abrasive to be used. Furthermore, if the tool compliance is adjustable in real-time, this could allow for maximizing cut rates during sanding of the part.

Embodiments herein disclose several variable compliance damper systems that change the amount of compliance in the tool as it interacts with the part being sanded. This can allow for real-time adjustability of the compliance in the tool. Variable compliance damping systems provide significant benefits for robotic abrading systems. The ability to control the force applied depending on given abrasive application parameters is incredibly useful. Variable force control systems described herein allow for both real-time adjustment of applied force in a system, for example based on feedback received during an operation, as well as pre-programmed force application cycles. Systems and methods herein can include active controls to monitor abrasion and adjust applied force accordingly.

Systems and methods herein can also be coupled with a vision system, or based on known trajectories of a repair path. For example, when an abrading system is approaching a corner, a viscosity of a magnetorheological fluid-based damper could be increased, providing more compliance. A vision system, or a known trajectory, can provide cues as to when to increase or decrease compliance based on an anticipated path.

A vision system may also detect a material being abraded to determine initial compliance settings. For example, a robotic sander may be sanding an airplane and may approach a window and round a corner. If the robotic system can detect the window coming, compliance can be adjusted accordingly.

Compliance changes are needed based on a variety of factors, including orientation changes, which adjust the application of gravitational forces on an abrasive article, as well as the need for more or less force based on features of the worksurface. Today this is done based on feedback from sensors that know the tool angle / weight and vary force from a force compliance tool accordingly. Systems and methods herein can also adjust compliance by adjusting viscosity of compliant dampers.

Currently, a single sanding tool may interface with a plurality of backup pads based on operation parameters. For example, some operations require a low compliance foam backup pad while others require a firmer backup pad. Systems and methods herein envision a compliance system built into a backup pad that can provide variable compliance without the need to swap out backup pads. Such a backup pad may have an interface that connects to a sanding tool. The interface may allow for power to be drawn from the tool. Some backup pads may be powered by an internal power supply.

Many of the figures systems and methods herein are illustrated as implemented in hand tool embodiments. However, this is for ease of understanding only and it is expressly contemplated that any or all may be implemented in a robotic abrading system.

<FIG> illustrate an orbital sanding took in which embodiments of the present invention may be useful.

<FIG> and <FIG> illustrate a random orbital sander <NUM> with a housing <NUM> having a hand grip <NUM> at a first end. While the housing <NUM> is shown as cylindrical, it can be formed in other configurations while still keeping within the scope of this disclosure. Connected to the second end of the housing, in some embodiments, is a lock ring that is adapted to secure a motor <NUM> within the housing <NUM>. The random orbital sander <NUM> may also include a particulate matter collection skirt <NUM> that is coupled to the lock ring <NUM>. The particulate matter collection skirt <NUM> is adapted to contain particulate matter created by the sander and, when used with a vacuum attachment, can be used to allow the dust the be collected by a vacuum unit. Located adjacent the particulate matter collection skirt <NUM> is a sanding pad <NUM> that is coupled to the motor <NUM>. The housing <NUM> also includes a valve assembly <NUM> that is adapted to be connected to a pressurized air supply. The valve assembly <NUM> is operated by depressing actuation lever <NUM>. While the housing <NUM> is preferably made from plastic it can also be manufactured metal, such as aluminum, or other materials.

<FIG> illustrates a cutaway view of random orbital sander <NUM>.

<FIG> and <FIG> relate to pneumatically powered sanding tools. However, it is expressly contemplated that systems and methods herein may also be applicable to electric and battery powered handheld or robotic systems. 1C illustrates a cutaway view of an electric rotary sander.

A motor can be seen and is designated generally by reference numeral <NUM>. The motor <NUM> includes an armature <NUM> having an output shaft <NUM> associated therewith. The output shaft or drive spindle <NUM> is coupled to a combined motor cooling and dust collection fan <NUM>. In particular, fan <NUM> comprises a disc-shaped member having impeller blades formed on both its top and bottom surfaces. The impeller blades 36a formed on the top surface serve as the cooling fan for the motor, and the impeller blades 36b formed on the bottom surface serve as the dust collection fan for the dust collection system. Openings 18a formed in the platen <NUM> allow the fan 36b to draw sanding dust up through aligned openings 19a in the sandpaper <NUM> into the dust canister <NUM> to thus help keep the work surface clear of sanding dust. The platen <NUM> is secured to a bearing retainer <NUM> via a plurality of threaded screws <NUM> (only one of which is visible in FIG. 1C) which extend through openings 18b in the platen <NUM>. The bearing retainer <NUM> carries a bearing <NUM> that is journaled to an eccentric arbor 36c formed on the bottom of the fan member <NUM>. The bearing assembly is secured to the arbor 36c via a threaded screw <NUM> and a washer <NUM>. It will be noted that the bearing <NUM> is disposed eccentrically to the output shaft <NUM> of the motor, which thus imparts an orbital motion to the platen <NUM> as the platen <NUM> is driven rotationally by the motor <NUM>.

<FIG> illustrate a ball bearing based compliant damping feature for a sanding tool. Illustrated in <FIG> is a rotary sander <NUM> that is part of a sanding system <NUM>. However, while a rotary sander <NUM> is illustrated, it is expressly contemplated that other sanding tools, such as orbital, linear and random orbital may be used, in other embodiments. Sanding tool <NUM> is coupled to a backup pad <NUM>, which has a tool connecting feature <NUM>, which connects to a drive shaft of tool <NUM>. Backup pad <NUM> also has an abrasive article attachment surface <NUM>, which receives an abrasive article for a sanding operation, such as an abrasive disc.

Between backup pad <NUM> and tool <NUM> is a damping system that includes a pair of ball bearings <NUM> that ride in a groove <NUM> (illustrated in <FIG>). Each ball-bearing <NUM> is coupled to a compliant damper <NUM>, which are also coupled to tool <NUM>. As illustrated in <FIG>, compliant damper <NUM> is a magnetorheological shock absorber. Compliant damper <NUM> is a variable compliance damper, for example allowing a range of compliance options when actuated. While backup pad <NUM> is illustrated at a significant distance from tool <NUM> for ease of understanding, it is expressly contemplated that, in at least some embodiments, the compliance dampers264 are condensed such that the tool <NUM> and the backup pad <NUM> are in close proximity to one another, for example on the order of one or more millimeters apart.

Compliant dampers <NUM>, in the embodiment illustrated in <FIG>, are magnetorheological shock absorbers with a magnetorheological fluid that causes springs to expand and contract to absorb vibrations caused by operation of tool <NUM> during a sanding operation. However, other suitable shock absorbing mechanisms may be used in other embodiments.

<FIG> illustrate a magnetic fluid-based compliant damping feature for a sanding tool. <FIG> illustrates a top-down view of a backup pad <NUM> modified with a damping system. The backup pad includes a tool connector <NUM>, which connects to a drive shaft of the tool, and which is on an opposite side from an abrasive article receiving surface <NUM>.

Backup pad <NUM> includes a damping system with a first contact ring <NUM> and a second contact ring <NUM>. As illustrated in <FIG>, a flexible fluid container <NUM> is present within a housing of backup pad <NUM>. Fluid container <NUM> is filled with a magnetorheological fluid, in one embodiment, with a viscosity that can be altered when a current is applied to the wire coils that encircle, or are embedded within the fluid container <NUM>. In the embodiment illustrated in <FIG>, a current can be applied by one of spring-loaded mobile arms <NUM> making contact with either or both of contact rings <NUM> or <NUM>. As the viscosity of the fluid within container <NUM> changes, the firmness of backup pad <NUM> also changes.

In some embodiments, a second set of arms <NUM> are also needed, such that arms <NUM> and the second set of arms both contact a coiled conducting wire in order for sufficient current to flow and cause an electromagnetic field.

In another embodiment, a single coil is positioned within the magnetic fluid and receives a current that adjusts the viscosity of the magnetic fluid.

Alternatively, as illustrated by coils <NUM>, in one embodiment the fluid container <NUM> is encircled and current is applied using contacts <NUM>. Windings <NUM> are illustrated as used in conjunction with contacts <NUM>, and instead of contact rings <NUM>, <NUM>.

Using any of the systems illustrated in <FIG> may allow for adjusting a viscosity of a magnetorheological fluid in fluid container <NUM> such that it becomes more or less stiff. Viscosity can be adjusted by varying current, and thus the strength of the resulting electromagnetic field, or by varying the number of windings <NUM>.

<FIG> illustrate a telescoping drive shaft for a sanding tool. As illustrated in <FIG>, a telescoping driveshaft <NUM> couples tool <NUM> to backup pad <NUM>, in one embodiment of a dampened sanding tool <NUM>. Backup pad <NUM> includes a tool connecting side, which receives drive shaft <NUM> through a threaded portion <NUM> of shaft <NUM> coupling to threading of backup pad <NUM> (not shown in <FIG>). Backup pad <NUM> also includes an abrasive article connecting side <NUM>, which receives an abrasive article for a sanding operation.

Telescoping drive shaft <NUM> is capable of collapsing up and down such that a magnetorheological damping feature <NUM> can collapse or expand within shaft <NUM>. In the embodiment illustrated in <FIG>, telescoping drive shaft has a plurality of grooves such that the telescoping sections can rotate together as tool <NUM> rotates backup pad <NUM> and an abrasive article coupled to side <NUM>.

Telescoping drive shaft <NUM> also has a connection feature <NUM> that interlocks tool <NUM> to backup pad <NUM>. As illustrated in <FIG>, in one embodiment, the connection feature is a threaded shaft.

<FIG> illustrate a fluid-based damping feature for a sanding tool. <FIG> illustrates a sanding tool <NUM> with an external housing <NUM> that houses a motor, as illustrated. Within housing <NUM> is a fluid-filled bladder <NUM>. Fluid <NUM>, in one embodiment, is a magnetorheological fluid that can change viscosity when affected by a magnetic field. A magnetic field can be applied by running a current through a current-conducting medium, such as a wire <NUM> wrapped around bladder <NUM>. Current conducting element <NUM>, in some embodiments, is an insulated coil to prevent shorts.

One end of element <NUM> couples to a positive lead, and the other couples to a negative lead. The strength of the applied magnetic field can be varied by the amount of current and / or the number of windings of wire <NUM>. A single wire <NUM> on an exterior is illustrated in <FIG>, However, wire <NUM> may be within bladder <NUM>, in some embodiments. In another embodiment, a second wire <NUM> is present on an interior of bladder <NUM>, between bladder <NUM> and a motor.

While a single fluid bladder <NUM> is illustrated in <FIG> surrounding the entire motor, it is expressly contemplated that, in some embodiments, fluid bladder <NUM> may only be substantially between the top of a motor and the top of the housing <NUM>. Such an embodiment may limit the ability of the motor to move to just along axis <NUM>. In other embodiments, instead of a single fluid bladder <NUM>, a plurality of fluid bladders <NUM>, each surrounded by a current conducting element <NUM>, are present within housing <NUM>. The plurality of fluid bladders <NUM> may allow for at least some angular movement of the motor within housing <NUM>, as illustrated by axis <NUM>.

<FIG> illustrates an electronic control system which may operate in concert with damping systems described herein. Systems using compliant damping systems, such as rheological-based fluids or other shock absorbers under the control of an electronic control system can product damping as selected or specified by a program memory <NUM> stored in, or accessible by, the device.

A set of system operating conditions <NUM> are monitored by a control system of a sanding tool and are input to an electronic analog to digital converter (A/D) <NUM> that converts analog signals to a digital representation, which is then provided to a computing engine <NUM>. Operating conditions <NUM> may include RPM, temperature, axial acceleration, etc. Also input to the A/D is a force or displacement measurement sensed by a sensor <NUM> associated with a rheological damping element <NUM>. Sensor(s) <NUM> may be an accelerometer, force and/or displacement sensor or other sensors that determine the system operating conditions. Computing engine <NUM>, therefore, takes as inputs: the algorithm(s) of the program memory <NUM>, system operating conditions <NUM> and measurements from sensor(s) <NUM>.

In some cases, A/D <NUM>, program memory hardware <NUM>, and digital to analog converter (DAC) <NUM> are integrated into computing engine <NUM>. Computing engine <NUM> may be, in some embodiments, a microprocessor, microcontroller or other suitable computing device.

Program memory <NUM> programs the response of the computing engine <NUM>, for example setting parameters around how fast to respond, under what conditions as determined by the system operating conditions, etc., and this is output to digital to analog converter (DAC) <NUM> that converts the multiple inputs, using program memory algorithm <NUM>, through an amplifier <NUM> into a controlled current signal that controls the magnetic field provided by compliant damper <NUM>.

While only one rheological damper <NUM>, and one amplifier <NUM>, are illustrated in <FIG>, and discussed with respect to <FIG>, it is expressly contemplated that, in some embodiments, multiple dampers are present within a sanding system. In such system, program memory <NUM> may contain an algorithm that adjusts compliance of each damper based on sensed information from sensor <NUM>. In some embodiments the output of the computing engine <NUM> to the amplifier <NUM> may be an analog signal, in which case the DAC <NUM> is not required.

<FIG> illustrates a diagrammatic view of a sanding system in accordance with embodiments herein. The sanding system <NUM> includes a sanding tool <NUM> which couples to a backup pad <NUM>, which connects to an abrasive article <NUM>, such as an abrasive disc. The sanding tool <NUM> may be a linear sander, a rotary sander, an orbital sander or a random orbital sander. Sanding tool <NUM> includes a housing with an internal cavity that houses a motor <NUM>. The motor includes an output shaft that couples to backup pad <NUM>, or directly to an abrasive disc <NUM>.

In some embodiments, sanding tool includes a particulate collector <NUM> that, for example, applies a vacuum or otherwise collects particulates created during a sanding operation. In embodiments where sander <NUM> includes a particulate collector <NUM> that operates based on a vacuum, an air supply connection <NUM> may be present.

As illustrated in <FIG>, in different embodiments, either tool <NUM> and / or backup pad <NUM> may have a damping feature <NUM>, <NUM>. In some embodiments, damping features <NUM>, <NUM> are each components of a damping system that spans a connection between tool <NUM> and backup pad <NUM>. However, in some embodiments, the damping system is wholly contained within either sander <NUM> or backup pad <NUM>, such that one or the other of features <NUM>, <NUM> are either not present, or not active, during a sanding operation. For example, system <NUM> described herein wholly contains the damping system within the sanding tool <NUM>, while system <NUM> contains the damping system wholly within the backup pad <NUM>. In contrast, system <NUM> contains features <NUM>, <NUM> that are either part of tool <NUM> or backup pad <NUM>.

Sanding tool <NUM> has an actuator <NUM> that, when actuated, causes motor <NUM> to move abrasive disc <NUM> to move in a pattern for a sanding operation. In some embodiments, actuator <NUM> is only actuatable when sanding tool <NUM> has been plugged in or otherwise powered. In other embodiments, actuator <NUM> serves to power on and actuate motor <NUM>. In some embodiments, motor <NUM> directly causes movement of backup pad <NUM>, which then causes abrasive disc <NUM> to move.

In some embodiments, damping feature <NUM> and / or damping feature <NUM> are actuated in conjunction with sanding actuator <NUM>, that is the damping starts as soon as sander <NUM> begins a sanding operation. However, damping actuator <NUM> may also be mechanically actuated based on another event, such as a minimum counterforce applied by a workpiece against the abrasive disc <NUM> during a sanding operation, or a minimum vibratory activity.

An amount of compliance provided by damping features <NUM> and / or <NUM> is controlled by controller <NUM>. For example, many compliant damping features described herein include a magnetorheological fluid that can change viscosity under an applied magnetic field. Controller <NUM> may communicate with a damping feature <NUM>, <NUM> and activate, increase, decrease or deactivate current flow, causing a viscosity of a magnetorheological fluid to change.

<FIG> illustrates a method of providing damping to a sanding operation in accordance with embodiments herein. Method <NUM> may be implemented in any suitable sanding or grinding tool that is expected to produce vibrations during a grinding operation.

In block <NUM> a sanding tool is prepared. Preparing a sanding tool may include selecting and attaching a suitable backup pad to the tool, and / or selecting a suitable abrasive article for a sanding job. For example, as discussed in <FIG>, in some embodiments a backup pad <NUM> has features of a damping system that correspond to damping features on or associated with the sanding tool. Preparing the sanding tool may also include other steps <NUM>, such as attaching a particulate collection system.

In block <NUM>, a sanding operation is conducted. The sanding operation may be conducted using an orbital sander <NUM>, random orbital sander <NUM>, rotary sander <NUM>, or another sanding tool <NUM>, such as a linear sander.

In block <NUM>, a compliant damping feature is actuated. While block <NUM> is illustrated as following block <NUM>, it is expressly contemplated that, in some embodiments, actuating the sanding tool also actuates the damping feature. However, it is expressly contemplated that the damping feature may be separately actuated, for example when power to the sanding tool is initiated, or when a reaction force is exerted on the sanding system by a worksurface being sanded. The damping feature may be any suitable damping feature, such as a fluid feature <NUM> containing a magnetorheological fluid that has a manipulatable viscosity, such as that described in <FIG> and <FIG>, a ball-bearing-based damping system <NUM>, such as that described in <FIG>, a telescoping drive shaft, as described in <FIG>. Other damping systems <NUM> may also be possible.

The damping feature activated in block <NUM> may include components solely associated with the sanding tool, as illustrated in block <NUM>, for example incorporated into the drive shaft or otherwise housed within the housing of the sanding tool. In other embodiments, the components of the damping feature may be solely associated with, or wholly included within the backup pad, as illustrated by block <NUM>.

<FIG> illustrates an exploded view of the components of a robotic paint repair stack. As illustrated, the robotic paint repair stack <NUM> comprises a robot arm <NUM>, force control sensors and devices <NUM>, a grinding/polishing tool <NUM> with damping system <NUM>, a hardware integration device <NUM>, abrasive pad(s) and compounds <NUM>, a design abrasives process <NUM>, and data and services <NUM>. These elements may work together to identify defect locations and to implement a predetermined repair program using a deterministic policy for the identified defect, such as the policy discussed in co-owned and co-pending PCT Application No. <CIT>.

While human-operated sanding tools are discussed above as example embodiments, providing damping to a robotic grinding / polishing tool <NUM> through a damping feature <NUM> is also expressly contemplated herein. One area where robots are lacking behind their human counterparts is the ability to identify and adapt to the need for changing pressure of changing pressure when sanding over non-flat part features. Generally, this is handled today by using compliant abrasive products (such as abrasive nonwoven wheels or bristle products) that 'give' when unit pressure increases over the radius or edge of a part. This prevents changing part dimensions but at the expense of cut rate and abrasive selection. Alternatively, compliance is provided through a force control unit <NUM>, which adjusts a force applied to a sanding tool <NUM>.

By moving the compliance mechanism into the abrasive tool, itself, it could allow for any abrasive to be used. Furthermore, if the tool compliance is adjustable in real-time, this could allow for maximizing cut rates during sanding of the part. This could also reduce complexity in the robotic system by removing the need for a separate force control unit outside of the sanding tool.

Providing a damping system that can be adjusted and connected without the need for a separate force control sensors and devices <NUM> allows for more dynamic sanding systems that can more efficiently conduct grinding and polishing operations.

Claim 1:
A sanding system comprising:
a tool (<NUM>, <NUM>) with a motor (<NUM>) which, when actuated, drives movement of a drive shaft;
a backup pad (<NUM>, <NUM>) coupled to the drive shaft, wherein the backup pad is configured to receive an abrasive article (<NUM>), and wherein movement of the drive shaft causes movement of the abrasive article;
characterized in that a compliant damping unit is configured to provide variable compliance for the tool when the abrasive article is contacting a worksurface, wherein the damping unit comprises a magnetorheological fluid (<NUM>) that changes from a first viscosity to a second viscosity when an applied current is changed from a first current to a second current, wherein the magnetorheological fluid is housed in the backup pad (<NUM>) and wherein the current is applied to a contact ring (<NUM>, <NUM>) on a surface of the backup pad; and
an electronic controller that receives a system operating condition, sends a signal to the compliant damping unit based on the system operating condition.