Mobile drive unit having a conveyor module

A mobile drive unit includes a pivot between the front chassis unit and the rear chassis unit, which both support a support structure that pivotally supports a payload housing.

BACKGROUND

The invention relates to robotic devices and methods, and more particularly to a mobile drive unit for transporting a payload.

Movement of products in a modern warehouse environment, such as a package sort center, in which packages are moved within a facility, occurs on a vast scale. One means to sort packages (i.e., payloads) is to use mobile drive units to deliver packages to destinations designated by the ultimate final destination of the package. For example, mobile drive units can be used to organize packages based on delivery route, as determined based on a postal code or other package features. Mobile drive units are self-powered robotic devices that travel on the floor of the warehouse guided by, for example, fiducial markers in or on the floor.

Mobile drive units may use different mechanisms for loading, transporting, and unloading of payloads. One type of mobile drive unit waits until the payload is placed on or in the mobile drive unit's payload housing. To unload the payload, some mobile drive units use a lifting tray that pivots around one end of the tray to dump the payload, similar to how a dump truck functions.

Being able to monitor the status of payloads during transport, particularly which such payloads are not physically secured to the payload housing, is important. Further, mobile drive units sometimes encounter warehouse concrete floors that have irregularities, such as expansion joints or dips inherent in building process or caused by floor wear or damage.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A mobile drive unit (“MDU”)10includes a chassis assembly12of a vehicle, such as an autonomous or semi-autonomous robot, that supports a payload housing14, capable of carrying a package (or other payload) in a sort center. The term “payload” is used herein to refer to any item typically moved in commerce, including but not limited to boxes, envelopes (such as jiffy mailers or bubble packs), and the like.

According to the embodiments shown inFIGS. 1-3, chassis12is a split chassis that includes a front chassis unit and a rear chassis unit that are hinged together such that upon encountering a floor irregularity, the front and/or rear chassis can move about a pivot. The pivoting feature of chassis12enables the overall height of the mobile drive unit to have a diminished height compared with prior generations of like robots.

Chassis12of mobile drive unit10includes a first chassis assembly, such as front chassis assembly or unit20, and a second chassis assembly, such as rear chassis assembly or unit60. Front chassis assembly20includes a base22, a pair of motorized wheel assemblies24L and24R, and a front caster26. Base22in the embodiment shown in the figures is a one-piece aluminum casting to which the wheel assemblies24L and24R and front caster26are mounted. Base22includes mounts and cut outs for receiving the wheel assemblies24L and24R, and includes a recess for mounting front caster26. Base22also includes a pair of pivot mounts70, as explained more fully below.

Rear chassis assembly60includes a base62and rear caster66. Base62preferably is a one-piece aluminum casting that includes a recess for mounting rear caster66. Rear chassis assembly60includes a pair of forward-extending arms that engage pivot mounts70of front base22. A pair of pins71(FIG. 1) link arms to mounts70to enable front base22and rear base62to pivot relative to each other. Pins71define a chassis pivot axis PA (FIG. 1) about which bases22and62pivot or rotate as needed. Axis PA is horizontal and transverse. Axis PA is also perpendicular to a direction of forward motion, which is illustrated inFIG. 1by line CL, as in the embodiment shown the direction of forward motion is parallel to the centerline CL of MDU10. Centerline CL bisects the bases20and60and is equidistant between the drive wheel assemblies24L and24R.

Front casters26and66are mounted to base22and62(respectively)—the caster shafts extend through the base and are affixed by bolts72. Preferably, casters26and66are conventional, and may include double wheels. Casters26and66freely pivot about the vertical axis through the shafts and are not driven. In the embodiment shown inFIG. 1, casters26and66are laterally offset from centerline CL. For example,FIG. 1shows front caster26spaced apart from centerline CL to the left and rear caster26spaced apart from centerline CL to the right. The offset spacing enables the drive unit8to pass over a fiducial marker, such as a bar code or3D code, in the floor without any of the wheels contacting the marker. Thus, the centerline CL of MDU10passes directly over a fiducial marker when the unit10drives forward.

Each motor assembly24L and24R includes a conventional motor42L and42R (as will be understood by persons familiar with mobile drive unit technology) and a drive wheel40L and40R, respectively. Wheels40L and40R are approximately at the midpoint (fore and aft) of mobile drive unit10. Each wheel40L and40R may be driven according to control signals to move unit10forward, or a direction of one of the wheels40can be reversed such that the drive unit10can rotate in place.

Referring toFIG. 7, mobile drive unit10can include a front cover28that is affixed to front base22and a rear cover68that is affixed to rear base62. Each cover28and68have a cut-out portion that, with the corresponding cut-outs in bases22and62, forms wheel cut-out that wheels40L/40R extend through. In this regard, wheels40L and40R may extend laterally to the outboard sides of mobile drive unit10.

Each one of front base22and rear base62includes a support structure98or mounts99for mounting a support structure98, as explained below and shown schematically inFIGS. 1-3.

Support structure98may support a payload housing14. Payload housing14can include any structure. Accordingly, support structure98may be any configuration and are shown only for illustration, as will be understood and can be implemented by persons familiar with mobile drive unit technology and depending on the particular parameters of the application. Different embodiments of payload housing14are discussed in more detail below.

Mounts99may have any configuration and supports that connect to mounts99may take any configuration, as, generally, mounts99encompass (without limitation) pivots and fixed structure. For example,FIGS. 1-3illustrates embodiments in which front mounts99F fixedly connect front support structure98F to unit22and rear mounts99R pivotally connect rear mounts99R to unit62. In other embodiments, the front mounts99F may be pivots and rear mounts may be fixed. Including a pivot mount allows a structure supported by support structure to support the payload while front and rear chassis pivot at mount70to enhance the function of the mobile drive unit. For example, pivot mounts at99and70promote traction of the main drive wheels40R and40F when the mobile drive unit encounters a floor irregularity. In this regard, as unit62moves over irregularities in the driving surface, pivot mount99R can adjust accordingly.

As discussed above, it may be desirable to maintain horizontal stability of a top surface102of payload housing14in spite of relative vertical movement of units22and62as mobile drive unit10traverses uneven surfaces.FIGS. 1-3illustrate different embodiments of support structures98that increase stability of payload housing14.

FIG. 1illustrates support structures98that are pivotally connected to payload housing14via pivots106. For example, each support structure98includes two pivot mounts106. During use, pivot connections106may cooperate with pivot mount99R to allow support structures98to move relative to mobile drive unit10and payload housing14. These pivot mounts98do not restrict top surface102of payload housing14to stay within a plane parallel to either unit22or62. Instead, pivot mounts98enable top surface102of payload housing14to remain horizontally planar, or at least closer to horizontally planar than unit22or62.

Support structure98may also include structures for dampening or isolating vibration generated by mobile drive unit10. For example, the embodiment inFIG. 2includes a vibration isolator111at support structure98R. Vibration isolator111can include any type of passive or active structure for isolating or dampening vibration. As another example, support structure98may include one or more dampening springs. The embodiment inFIG. 3illustrates each support structure98as comprising a top support structure112A connected to a bottom support structure112B via one or more vertical springs115.

In some embodiments, different placement of vibration isolator111may increase its effectiveness. For example, in some embodiments, including vibration isolator111on pivot connection106, and more particularly on a top pivot connection106, is more effective for decreasing vibrational forces upon a payload relative to other positions.

As discussed above, support housing98supports payload housing14. Payload housing14in turn may support different components for securing, holding, or moving a payload. The payload may reside on top surface102of payload housing14. Payload housing14may include one or more walls104that rise above top surface102. For example,FIG. 1illustrates payload housing14with two walls104, one on each side of payload housing14. As shown inFIG. 2, these walls104may include eyelets at the top.FIG. 7illustrates payload housing14with an additional wall104between two conveyor belt assemblies108. During use, such frames104decrease the likelihood that the payload will bounce or slide off of the sides of top surface102, despite any jolting or vibration caused by uneven drive surfaces. In some embodiments, a controller is used to raise or lower walls104.

As shown inFIG. 7, walls104may be fixed or moveable.FIG. 7Ashows wall104including a spring109that allows wall104to raise or lower. This ability to raise or lower may be passive; for example, spring109may be compressed by the weight of a package placed on wall104. As another example, a controller107may be used to engage/disengage spring109. This provides flexibility for payload housing14to support payloads of varying shapes and sizes. For example, in some uses, the footprint of the payload may extend beyond the footprint of payload housing14itself.

In some embodiments, payload housing14may include one or more sensors106that detect the presence, location, or movement of a payload on top surface102. For example, such sensors may include pressure sensors integrated into top surface102. As another example, as shown inFIGS. 4, 6, and 9, motion or distance sensors (e.g., infrared sensors or other light sensors) may be integrated into walls104. Such sensors106may be strategically placed to detect when a payload is at risk of falling off the front or back of top surface102. For example, while not shown, sensor106may be integrated along CL. Additionally or alternatively, as shown, sensors106may be integrated within a certain distance from the edge of top surface102. The sensor information may be used to adjust placement of the payload relative to payload housing14. This adjustment is discussed in more detail below with respect to different mechanisms for moving the payload.

Payload housing14may include mechanisms for loading, unloading, or adjusting the position of a payload on top surface102. For example, as shown inFIGS. 1-5, payload housing14supports a conveyor belt assembly108. As another example, as shown inFIG. 7, payload housing14supports a powered roller assembly110. While the conveyor belt assembly108and powered roller assembly110are shown fixedly connected to payload housing14, as shown inFIGS. 1-8, payload housing14may include a turntable upon which conveyor belt assembly108or powered roller assembly110are installed, such that the conveyor belt assembly108or powered roller assembly110can rotate on a turntable119, as shown inFIG. 8.

As another example, payload housing14includes one or more ramps105at the front and rear of top surface102to facilitate onloading and offloading of payloads, as shown inFIG. 5. These ramps105can make the transition of the payload from or to a lower surface that top surface102smoother, which may be helpful in cases where the payload is fragile.

With reference toFIGS. 1-4, conveyor assembly108is discussed in more detail. Conveyor assembly108includes a conveyor motor114that drives one or more pulleys116. As shown inFIG. 1, conveyor motor114is supported by support structure98F. In turn, pulleys116move belt118. Conveyor assembly108operates to move a payload onto or off of top surface102. As discussed above, sensors106are used inFIG. 4to monitor the movement of a payload on top surface102. For example, as mobile drive unit10is traveling to an end point, sensors106may monitor the location of the payload. In the event the payload moves to close to either end of belt118, a controller120can cause conveyor motor114to adjust belt118. In this manner, conveyor assembly108can control placement of a payload.

For example, based on sensor data from sensor106, controller120can determine that a package on the conveyor belt assembly is within a threshold distance from an edge of conveyor belt118. This threshold may be variable, such as based on the size of the package, such as the relative size of the package to top surface102F. As another example, the threshold distance may be based on a change in the distance of the package from the edge of conveyor belt118during transport. In response to the package coming within the threshold distance of the edge of conveyor belt118, controller120can operate conveyor motor114to cause conveyor belt118to move the package away from the edge of conveyor belt118. This process can repeat as the package is jostled during transport.

Referring toFIG. 6, powered roller assembly110includes one or more rollers113that form top surface102on which a payload can be loaded. One or more rollers113may be powered by a motor. Powered roller assembly110also includes one or more support plates117between rollers113. These support plates117may prevent payloads from becoming stuck between rollers113.

The mobile drive unit includes controllers, cameras and other sensors, a docking port, a turntable, motors to lift and rotate the turntable, and the other components. A person familiar with mobile drive unit technology will understand how to mount and employ the additional components to the front and rear chassis units disclosed herein according to the particular goals and design of the mobile drive unit application.

The present invention has been described by employing a particular embodiment to illustrate particular features. For merely one non-limiting example, components are referred to as front and rear in order to illustrate the structure and function, but the invention is not limited to the particular front and rear orientations unless expressly stated in the claims. Further, the present invention is not limited to any structure or function, nor is the invention limited to any solution to any problem, described herein unless expressly stated in the claims. Nor is the invention limited in any way to embodying a benefit unless expressly stated in the claims. Rather, the structure and function described herein is merely an illustration, and the claims are intended to receive their full scope.