Mobile robot braking

Abstract

A mobile robot has a front, a rear, a left side, and a right side. The mobile robot comprises a payload section (110) configured to support a payload; a drive section (105) comprising a drive wheel (160) and disposed forward of the payload section; and a dual axis bogie suspension (107) coupling the payload section to the drive section. The dual axis bogie suspension is configured to provide a first pivotable coupling (135) between the dual axis bogie suspension and the payload section. The first pivotable coupling provides a first axis of rotation (140) that extends frontward and rearward, and a second pivotable coupling (315, 320, 325) that provides a second axis of rotation (155) that extends laterally between the left and right sides of the mobile robot. The second axis of rotation is disposed between the drive wheel (160) and the first pivotable coupling.

Description

[0001] MOBILE ROBOT BRAKING

[0002] TECHNICAL FIELD

[0003] This invention relates to mobile robots, and more particularly to designs of mobile robots with improved braking performance.

[0004] BACKGROUND

[0005] Mobile robots are robots that are capable of moving in their surroundings. Mobile robots have become more commonplace in a variety of settings. For example, hospitals use mobile robots to move materials. Warehouses have installed mobile robotic systems to efficiently move materials from stocking shelves to order fulfillment zones. Mobile robots are also used in industrial, military and security settings.

[0006] Mobile robots can be autonomous in that they are capable of governing the performance of the programmed instructions independently. In other words, real-time control of operations by an external human or other operator is unnecessary for many actions. These autonomous operations can include defined actions that contribute directly to predefined operations (e.g., manufacturing products, transporting goods and materials, moving carts, cleaning, surveillance, disinfection, etc.) as well as actions that are responsive to unforeseen transient circumstances (e.g., identifying the position of movable obstacles and objects, including other autonomous mobile robots, responding to alarms or safety conditions, and the like).

[0007] Whether they are autonomous or not, the drive performance and safety of mobile robots is impacted by their design. In much the same way that an automobile with a high center of gravity may be at risk for rolling over, the design of a mobile robot can impact the kinematic behavior of mobile robots — as well as the safety parameters defined based on that kinematic behavior.

[0008] SUMMARY

[0009] Mobile robots with improved traction and braking performance are described.

[0010] In an implementation, a mobile robot has a front, a rear, a left side, and a right side. The mobile robot comprises a payload section configured to support a payload; a drive section comprising a drive wheel and disposed forward of the payload section ; and a dual axis bogie suspension coupling the payload section to the drive section. The dual axis bogie suspension is configured to provide a first pivotable coupling between the dual axis bogie suspension and the payload section. The first pivotable coupling provides a first axis of rotation that extends frontward and rearward, and a second pivotable coupling that provides a second axis of rotation that extends laterally between the left and right sides of the mobile robot. The second axis of rotation is disposed between the drive wheel and the first pivotable coupling.

[0011] This implementation and other implementations of the mobile robot can include one or more of the following features. For example, the mobile robot can further comprise a rotatable support disposed and configured to support a portion of the weight of the mobile robot; and a side frame that acts as a bogie arm and couples the rotatable support to the drive wheel with the drive wheel forward of the rotatable support and the second pivotable coupling disposed therebetween.

[0012] The side frame can comprise a pair of longitudinally-extending side members and a laterally extending member that couples the longitudinally-extending side members. A first of the longitudinally-extending side members can be coupled to a first rotatable support and a second of the longitudinally-extending side members is coupled to a second rotatable support and the laterally extending member is coupled to the drive wheel .

[0013] The dual axis bogie suspension can comprise a bolster member that is coupled to first pivotable coupling and to the side frame. The second pivotable coupling can couple the bolster member to the side frame .

[0014] In another implementation, a mobile robot has a front, a rear, a left side, and a right side. The mobile robot includes a drive wheel and a rotatable support disposed and configured to support a portion of the weight of the mobile robot; a bogie arm coupled to the drive wheel and to the rotatable support; and a coupling arrangement between a pivot point that provides the bogie axis and a payload section of the mobile robot. The drive wheel is coupled to the bogie arm forward of the coupling of the rotatable support to the bogie arm. The bogie arm is rotatable about a bogie axis that extends laterally between the left and right sides of the mobile robot between the drive wheel and the rotatable support. The coupling arrangement couples to the payload section rearward of the pivot point. This implementation and other implementations of the mobile robot can include one or more of the following features. For example, the coupling arrangement can comprise a pivotable coupling to the payload section. The pivotable coupling can be configured to provide a first axis of rotation that extends frontward and rearward.

[0015] The coupling arrangement can comprise a bolster member that couples the pivotable coupling to the payload section to the bogie arm . The rotatable support can be configured to rotate about a support axis that is disposed rearward of the bolster member . The bogie arm can be on the left side of the mobile robot. The mobile robot can comprise a second bogie arm on the right side of the mobile robot. The second bogie arm can be coupled to a second rotatable support and rotatable about the bogie axis of the bogie arm .

[0016] The bogie arm and the second bogie arm can be coupled by a laterally-extending member. A portion of the drive wheel can be disposed beneath the laterally-extending member. The bogie arm and the second bogie arm can both be coupled to the drive wheel . The payload section can include a vertically translatable lifting member . The rotatable support can be a caster. The drive wheel can be steerable.

[0017] The mobile robot can include a control unit configured to control performance of at least some operations by the mobile robot in accordance with instructions for performing operations as well as data relevant to the performance of those operations. Parameters defined in the instructions or data can reflect direction of a downwardly- directed force by the drive wheel during braking when the mobile robot is traveling in a forward direction.

[0018] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

[0019] DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a schematic side view of a mobile robot with improved braking performance.

[0021] FIG. 2 is a schematic top view of the drive section of the mobile robot of FIG. 1.

[0022] FIG. 3 is a schematic side view of a portion of a mobile robot with improved braking performance. FIG. 4 is a schematic exploded view of a portion of the mobile robot of FIG. 3. Like reference symbols in the various drawings indicate like elements.

[0023] DETAILED DESCRIPTION

[0024] FIG. 1 is a schematic side view of a mobile robot 100 with improved braking performance and FIG. 2 is a schematic top view of the drive section of mobile robot 100. Generally speaking, mobile robot 100 includes a drive section 105 and a pay load section 110. Drive section 105 is coupled to mobile robot 100 forward of pay load section 110 by a dual axis bogie suspension 107. In the illustration, the forward direction is indicated by a bold, solid arrow 30 and corresponds to the direction that mobile robot 100 is most likely to travel when in operation. The coupling between drive section 105 and payload section 110 with dual axis bogie suspension 107 improves driving performance, including traction during braking, when mobile robot 100 is moving in the forward direction.

[0025] In more detail, in the illustrated implementation, payload section 110 is schematically shown as a forklift-like structure with a mast 115 mounted to a chassis 120. One or more forks 125, platforms, or lifting members are vertically translatable along mast 115. A load 20 is shown supported on fork 125 in an elevated position relative to chassis 120. One or more wheels 130 are rotably coupled to the rear of chassis 120 and — along with one or more casters 165 and one or more drive wheels 160 in drive section 105 — support mobile robot 100 on the floor 10. For example, payload section 110 can include a pair of wheels 130, one to the left and one to the right of mobile robot 100 when mobile robot 100 is viewed from the front. Regardless of their number, wheels 130 can rotate about a wheel axis. In some implementations, wheels 130 are also casters and can rotate about a vertical axis, i.e., an axis that is parallel to the plane of the page in FIG. 1 and in and out of the plane of the page in FIG. 2.

[0026] Payload section 110 is coupled to dual axis bogie suspension 107 at a rotational coupling 135 that provides a first rotational axis 140. Rotational axis 140 extends longitudinally forward and rearward, parallel to the plane of the page in both FIG. 1 and FIG. 2, near the lateral middle of both payload section 110 and drive section 105. In the illustrated implementation, rotational coupling 135 is shown partway along the vertical height of mast 115. However, rotational coupling 135 can be positioned in different locations so long as the connection to pay load section 110 is able to withstand the loads borne by robot 100. For example, rotational coupling 135 can be positioned at the vertical level of the chassis 120. Rotational axis 140 provides for relative rotational movement between drive section 105 and pay load section 110. The rotational coupling between payload section 110 and dual axis bogie suspension 107 at first rotational axis 140 can be implemented in a variety of different ways including, e.g., axles, roller bearings, and the like. The rotational coupling can be direct or mediated by one or more intermediate elements.

[0027] As part of dual axis bogie suspension 107, rotational coupling 135 is coupled to a bolster member 145 that is rotably coupled to a side frame 150. Side frame 150 acts as a bogie arm and the rotational coupling between bolster member 145 and side frame 150 provides the second rotational axis 155 of dual axis bogie suspension 107. Second rotational axis 155 extends laterally perpendicular to first rotational axis 140. With payload section 110 and drive section 105 in the neutral position with respect to first rotational axis 140, second rotational axis 155 is perpendicular to the plane of the page in FIG. 1 and parallel to the plane of the page in FIG. 2. However, relative rotation between payload section 110 and drive section 105 about first rotational axis 140 will change the orientation of second rotational axis 155 with respect to the plane of the page, but second rotational axis 155 will remain generally perpendicular to first rotational axis 140. The rotational coupling between bolster member 145 and side frame 150 at second rotational axis 155 can be implemented in a variety of different ways including, e.g., axles, roller bearings, and the like. The rotational coupling can be direct or mediated by one or more intermediate elements.

[0028] In any case, side frame 150 can rotate relative to bolster member 145 about second rotational axis 155. One or more casters 165 are mounted to side frame 150 rearward of second rotational axis 155 and one or more drive wheels 160 are mounted to side frame 150 forward of second rotational axis 155. Both caster(s) 165 and drive wheel(s) 160 can rotate about their respective wheel axes and about respective vertical axes. The rotation of drive wheel(s) 160 about the vertical axis / axes is driven by one or more steering motors 170 to steer mobile robot 100. The rotation of caster(s) 165 about their respective vertical axis / axes stabilizes mobile robot 100 during turning. The rotation of drive wheel(s) 160 about the wheel axis / axes is driven by one or more drive motors (not shown). Drive wheel(s) 160 and caster(s) 165 — along with any drive motor(s), steering motor(s) 170, and their respective power supplies — form drive section 105.

[0029] The rotation about first rotational axis 140 and second rotational axis 155 increases the likelihood that front drive wheel(s) 160 and caster(s) 165— as well as wheels 130— will remain in contact with floor 10. By way of example, if side frame 150 were not able to pivot about second rotational axis 155, then forward movement of mobile robot 100 from a flat floor 10 onto an upwardly-inclined ramp could elevate caster(s) 165 out of contact with floor 10. As another example, rotation about first rotational axis 140 allows a drive section 105 with multiple, laterally-spaced drive wheels 160 and / or casters 165, to traverse and remain in contact with floors 10 that are laterally sloped or uneven.

[0030] In the illustrated implementation, side frame 150 is generally U-shaped when viewed from above or below with a pair of longitudinally-extending arms of the U joined by a laterally-extending member at the bottom of the U. The longitudinally-extending arms are disposed along the left and right sides of bolster member 145 and act as a single bogie arm because of their coupling by the laterally-extending member. At its rear, each longitudinally-extending arm of side frame 150 mounts a respective caster 165. As discussed above, casters 165 are each able to rotate about a respective vertical axis and wheel axis. Relative rotation between pay load section 110 and drive section 105 about first rotational axis 140 will change the orientation of the caster axes and wheel axes of casters 165 with respect to the plane of the page.

[0031] In the illustrated implementation, the laterally-extending member in side frame 150 is positioned forward of bolster member 145 and supports a single drive wheel 160 and an associated steering motor 170. Steering motor 170 is coupled to rotate drive wheel 160 about axis 175. In general, the shaft of steering motor 170 is mounted coaxially with respect to axis 175 and can rotate arms or other members that support the axle of drive wheel 160. However, in other implementations, rotational or even linear movement can be coupled from steering motor 170 to drive wheel 160 by gears, chains, or other intervening members.

[0032] Drive wheel 160 is driven by a drive motor (not shown). In many implementations, the drive motor is electric and powered by a battery. In general, drive wheel 160 will include an outer surface that is configured to generate traction on floor 10 or other surface on which mobile robot 100 will typically travel during operation. For example, drive wheel 105 can include treads and / or be made from rubber or other material with a relatively high coefficient of friction on the operational surface.

[0033] In the illustrated implementation, dual axis bogie suspension 107 is not steerable, i.e., side frame 150 does not rotate about a vertical axis that is in a plane that is parallel to the plane of the page in FIG. 1 or goes into and out of the plane of the pages in FIG. 2. However, this is not necessarily the case and in some cases bolster member 145 can rotate about a center pivot (not shown).

[0034] FIG. 3 is a schematic side view of a portion of a mobile robot 300 with improved braking performance and FIG. 3 is a schematic exploded view of a portion of mobile robot 300. Some characteristics of mobile robot 300 differ from those of mobile robot 100; however, many of components play similar roles and have similar features. The components that play similar roles are designated with like reference numbers in robots 100, 300.

[0035] Focusing on some of the differences between mobile robots 100, 300, in mobile robot 300, the dual axis bogie suspension 107 is more compact in the forward / rearward longitudinal direction such that drive wheel 105 is closer to pay load section 110 and the flexural load borne by rotational coupling 135 is lessened.

[0036] This longitudinal compactness is achieved by various characteristics of bolster member 145 and side frame 150. For example, bolster member 145 includes a plate 305 and a pair of arms 310. Plate 305 includes a front face and a rear face that together define a front-to-back longitudinal thickness. As can be seen from the lateral side faces of plate 305, the longitudinal thickness of plate 305 from front-to-back is less that the vertical dimension and lateral dimension of plate 305. With robot 300 assembled, plate 305 extends vertically from rotational coupling 135 down to arms 310, each of which is positioned on a respective lateral side of plate 305 and extends in the forward direction past the front face of plate 305. Arms 310 each include a portion 315 that, together with a respective corresponding portion 320 of side frame 150, form a respective pivotable coupling. The pivotable couplings define second rotational axis 155. In the illustrated implementation, the pivotable couplings each includes a hole 315 in an arm 310 and a corresponding hole 320 in side frame 150, as well as an axle member 325 about which bolster member 145 and side frame 150 can rotate.

[0037] In addition to hole 320, side frame 150 also includes a central bridge 330, a pair of rearwar dly-extending longitudinal arms 335, and a forwardly-extending longitudinal arm 340. Central bridge 330 has front face and a rear face that together define a longitudinal thickness that is less than the vertical dimension and lateral dimension of central bridge 330. Central bridge 330 is a generally shaped like a U that is inverted with respect to floor 10, with the arms of the U disposed on lateral sides of central bridge 330 and including a portion 320 that helps define second rotational axis 155. In the illustrated implementation, the empty space between the arms is dimensioned to pass above and accommodate at least some of drive wheel 160, regardless of the orientation drive wheel 160 with respect to the forward direction of travel (i.e., regardless of the rotational position of drive wheel 160 about axis 175). This contributes to the compactness of the longitudinal dimension of dual axis bogie.

[0038] Rearwardly-extending longitudinal arms 335 are coupled near the bottom of central bridge 330 and extend rearward. Each arm 335 includes a portion 345 of a pivotable mount for a respective caster 165. In the illustrated implementation, longitudinal arms 335 extend rearwardly to an extent sufficient for the wheel axis of casters 165 to be rearward of bolster member 145, regardless of the rotational position of casters 165 about their vertical caster axes. In some implementations, longitudinal arms 335 extend rearwardly such that the wheel axis of casters 165 is always rearward of rotational coupling 135.

[0039] As for forwardly-extending longitudinal arm 340, only the foremost portion of forwardly-extending longitudinal arm 340 is shown in FIGS. 3 and 4. In the exploded view of FIG. 4, the forwardly-extending longitudinal arm 340 does not appear to be coupled to the remainder of side frame 150. However, for side frame 150 to act as a bogie member, forwardly-extending longitudinal arm 340 is coupled to the remainder of side frame 150 and couples drive wheel 160 to side frame 150 at a position that is forward of the vertical plane that intersects second rotational axis 155. In other words, the assembly of forwardly-extending longitudinal arm 340, central bridge 330, and r earwar dly- extending longitudinal arms 335 act as single mechanical unit that pivots about second rotational axis 155 to raise drive wheel 160 and lower casters 165, or vice- versa.

[0040] In general in the static condition when any mobile robot — including mobile robots 100, 300 — is not moving, a portion of the static load arising from the weight of mobile robot and any payload will be borne by its drive wheel — as well as casters, wheels, or other supports that contact the supporting surface. The distribution of the loads amongst the drive wheel and these other supports will depend on several factors, including the geometry of mobile robot, the features of the floor or other surface, and the distribution of any payload.

[0041] When the mobile robot is moving, the drive wheel may slip. The slippage may occur, e.g., during acceleration and braking, during turning, or when the mobile robot drives up ramps, over obstacles, or the like. The precision of the control of the mobile robot is decreased. Further, in some mobile robots, the position of mobile robot during navigation is calculated using a rotary encoder or other device that measures rotation of a drive wheel and acts as an odometer. Slippage of such a drive wheel may lead to incorrect or inaccurate location and navigation information.

[0042] Increasing the traction between the drive wheel and the floor or other supporting surface will reduce this slip. The traction between the drive wheel and the supporting surface can be increased, e.g., by increasing the load borne by the drive wheel. Depending on details of mobile robot, increasing the load borne by the drive wheel may also increase the load borne by casters or other supports that are in contact with a floor or other surface. This may be undesirable when, e.g., the other supports are casters that should rotate freely as the mobile robot changes direction. Turning to the illustrated mobile robots 100, 300, during braking, as mobile robots 100, 300 travel in the forward direction, the forward inertia of a payload that is mounted on fork 125 will apply a forwardly- directed force to mobile robot 100, 300. The forwardly-directed inertial force will tend to increase the contact force — and hence friction and traction— between drive wheel 160 and the floor 10 or other surface on which mobile robot 100, 300 is traveling. Indeed, by positioning drive wheel 160 forward of axis 155 of dual axis bogie suspension 107 and the rotational support rearward of axis 155, the contact force of drive wheel 160 will increase more than it would have increased had drive wheel 160 been positioned, e.g., rearward of axis 155 (and the rotational support 130 positioned forward of axis 155).

[0043] Further, since the weight of the payload will impact the magnitude of the increase in the contact force at drive wheel 160, the increases in friction between drive wheel 160 the floor 10 will also be tailored to the weight of the pay load. In general, a weightier payload will lead to higher increases in friction. Braking performance is thus, to some extent, tailored to the payload. The improved braking performance can decrease the stopping distance for the robot.

[0044] Further, in implementations in which a control unit controls performance of operations by mobile robot 100, 300 (for example, where mobile robot 100 is autonomous), the operational parameters that are defined as safe can reflect the improved braking performance during travel in the forward direction. For example, operational parameters encompassed by permitted (or “safe”) envelopes can be enlarged and / or the operational parameters encompassed by excluded (or “unsafe”) envelopes can be decreased.

[0045] The number and arrangement of drive wheel 160, wheels 130, and casters 165 can vary in different implementations of mobile robot 100, 300. For example, the illustrated implementations include two front casters 165, two rear wheels 130, and a single drive wheel 160. Each front caster 165 and each rear wheel 130 is positioned on one lateral side of mobile robot 100 and drive wheel 160 is positioned near the lateral middle.

[0046] In other implementations, mobile robots 100, 300 can include multiple drive wheels 160. For example, the drive wheels 160 can be positioned laterally adjacent to one another with the rotational position about their respective vertical axes locked. In some implementations, mobile robots 100, 300 includes a single front caster 165 and / or a single rear wheel 130. In other implementations, mobile robots 100, 300 can include more than two front casters 16, more than two rear wheels 130, and / or more than two drive wheels 160.

[0047] More generally, in other implementations, mobile robots 100, 300 can be supported on floor 10 by wheels, tracks, rollers or other components that both support a robot and allow it to move along the relevant surface(s). These other components can provide support in addition to wheel(s) 130 and caster(s) 165 or as substitutes for wheel(s) 130 and caster(s) 165.

[0048] As discussed above, in some implementations, mobile robots 100, 300 are autonomous. Autonomous mobile robots are mobile machines that can move to perform actions in accordance with programmed instructions. Autonomous mobile robots are autonomous in that they are capable of governing the performance of the programmed instructions independently. In other words, real-time control of operations by an external human or other operator is unnecessary for many work-day actions. These autonomous operations can include defined actions (e.g., manufacturing products, transporting goods and materials, moving carts, cleaning, surveillance, disinfection, etc.) as well as actions that are responsive to transient circumstances (e.g., identifying the position of movable obstacles and objects, including other of autonomous mobile robots, responding to alarms or safety conditions, and the like). The instructions are generally stored within the autonomous mobile robots themselves. However, in some implementations, instructions can be stored externally to the autonomous mobile robots and transmitted to the autonomous mobile robots as needed.

[0049] The instructions of an autonomous mobile robot are generally implemented by a control unit that is included in the autonomous mobile robot. Such control units will generally include both hardware and software components that interoperate to control the performance of operations. The hardware components can include control circuitry, data processor(s), and data storage. Analog, digital, or both analog and digital processing can be performed. The stored information can include the instructions for performing operations as well as data relevant to the performance of those operations. Examples of relevant data can include, e.g., an electronic map for navigation, the shape of various workpieces, and definitions of safety zones and envelopes.

[0050] The program instructions that are performed by autonomous mobile robot 100 can reflect the improved braking performance during braking as the mobile robot 100 travels in the forward direction. For example, the operational parameters encompassed by permitted (or “safe”) zones and envelopes can be enlarged and / or the operational range encompassed by excluded (or “unsafe”) zones and envelopes can be decreased.

[0051] In general, both autonomous and non-autonomous mobile robots 100, 300 will have features that reflect that movement in the forward direction is most likely during operation. For example, mobile robots 100, 300 will generally be able to travel faster in the forward direction than in the rearward direction. As another example, LIDAR or other sensors may have a larger range or a higher resolution in the forward direction than in the rearward direction. As yet another example, the steering or braking performance of a mobile robot may be better for travel in the forward direction than for travel in the rearward direction. Also, the program instructions that are performed by autonomous mobile robot 100 may reflect that movement in the forward direction is most likely in a number of different ways. For example, the instructions may cause an autonomous mobile robot 100 to beep or otherwise indicate that the mobile robot 100 is traveling in the rearward direction. Safety zones and envelopes may be defined differently for forward and rearward travel.

[0052] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A mobile robot having a front, a rear, a left side, and a right side, the mobile robot comprising: a payload section (110) configured to support a payload; a drive section (105) comprising a drive wheel (160) and disposed forward of the payload section (110); and a dual axis bogie suspension (107) coupling the payload section (110) to the drive section (105), wherein the dual axis bogie suspension (107) is configured to provide a first pivotable coupling (135) between the dual axis bogie suspension and the pay load section (110), wherein the first pivotable coupling provides a first axis of rotation (140) that extends frontward and rearward, and a second pivotable coupling (315, 320, 325) that provides a second axis of rotation (155) that extends laterally between the left and right sides of the mobile robot, wherein the second axis of rotation is disposed between the drive wheel (160) and the first pivotable coupling.

2. The mobile robot of claim 1, further comprising: a rotatable support (165) disposed and configured to support a portion of the weight of the mobile robot; and a side frame (150) that acts as a bogie arm and couples the rotatable support (165) to the drive wheel (160) with the drive wheel (160) forward of the rotatable support (165) and the second pivotable coupling disposed therebetween.

3. The mobile robot of claim 2, wherein the side frame (150) comprises a pair of longitudinally-extending side members and a laterally extending member that couples the longitudinally-extending side members, wherein a first of the longitudinally- extending side members is coupled to a first rotatable support (165) and a second of the longitudinally-extending side members is coupled to a second rotatable support (165) and the laterally extending member is coupled to the drive wheel (160).

4. The mobile robot of claim 2 or 3, wherein the dual axis bogie suspension comprises:a bolster member (145) that is coupled to first pivotable coupling (135) and to the side frame (150), wherein the second pivotable coupling couples the bolster member (145) to the side frame (150).

5. A mobile robot having a front, a rear, a left side, and a right side, the mobile robot comprising: a drive wheel (160) and a rotatable support (165) disposed and configured to support a portion of the weight of the mobile robot; a bogie arm (150) coupled to the drive wheel (160) and to the rotatable support (165), wherein the drive wheel (160) is coupled to the bogie arm (150) forward of the coupling of the rotatable support (165) to the bogie arm and wherein the bogie arm (150) is rotatable about a bogie axis (155) that extends laterally between the left and right sides of the mobile robot between the drive wheel (160) and the rotatable support (165); and a coupling arrangement between a pivot point that provides the bogie axis (155) and a payload section (110) of the mobile robot, wherein the coupling arrangement couples to the pay load section (110) rearward of the pivot point.

6. The mobile robot of claim 5, wherein: the coupling arrangement comprises a pivotable coupling (135) to the payload section (110), wherein the pivotable coupling (135) is configured to provide a first axis of rotation (140) that extends frontward and rearward.

7. The mobile robot of claims 6, wherein: the coupling arrangement comprises a bolster member (145) that couples the pivotable coupling (135) to the payload section (110) to the bogie arm (150).

8. The mobile robot of claim 7, wherein the rotatable support (165) is configured to rotate about a support axis that is disposed rearward of the bolster member (145).

9. The mobile robot of any one of claims 5 to 7, wherein: the bogie arm (150) is on the left side of the mobile robot; the mobile robot comprises a second bogie arm (150) on the right side of themobile robot, wherein the second bogie arm (150) is coupled to a second rotatable support (165) and rotatable about the bogie axis (155) of the bogie arm (150).

10. The mobile robot of claim 9, wherein: the bogie arm and the second bogie arm are coupled by a laterally-extending member; and a portion of the drive wheel (160) is disposed beneath the laterally-extending member.

11. The mobile robot of claim 9 or 10, wherein the bogie arm and the second bogie arm are both coupled to the drive wheel (160).

12. The mobile robot of any of claims 1 to 11, wherein the pay load section (110) includes a vertically translatable lifting member (125).

13. The mobile robot of any of claims 1 to 12, wherein the rotatable support (165) is a caster.

14. The mobile robot of any of claims 1 to 13, wherein the drive wheel (160) is steerable.

15. The mobile robot of any of claims 1 to 14, wherein the mobile robot includes a control unit configured to control performance of at least some operations by the mobile robot in accordance with instructions for performing operations as well as data relevant to the performance of those operations, wherein parameters defined in the instructions or data reflect direction of a downwardly- directed force by the drive wheel (160) during braking when the mobile robot is traveling in a forward direction.

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