Acceleration control elements for a mobile driving unit

Abstract

Mobile driving unit with a linear acceleration value and an angular acceleration value, the mobile driving unit comprising: a chassis assembly having a pair of drive wheel assemblies, each drive wheel assembly including a motor; a front and a rear roller, each connected to the chassis assembly; a support structure mounted on the chassis assembly; a cargo enclosure mounted to the support structure, the cargo enclosure including a top surface; a controller communicatively connected to the drive wheel assemblies of the center chassis; and a memory that stores instructions that cause the controller to perform operations, the operations including: Determining a mass of a charge located on the upper surface; Defining a permissible maximum linear acceleration based on the linear acceleration value and the mass of the load; Determining a previous directional movement of the mobile driving unit, the previous directional movement indicating a direction of the front roller and the rear roller; Determining a next directional movement of the mobile driving unit which is different from the previous directional movement; Defining a maximum allowable angular acceleration and maneuvering angle based on the previous directional movement and the next directional movement, such that the maximum allowable angular acceleration is lower than a standard acceleration value for a given number of degrees or distance traveled to align the direction of the front roller and the rear roller; if the next directional movement involves a turn, causing the motors to operate at the maximum permissible angular acceleration for at least the maneuvering angle; and if the next directional movement involves a linear movement, causing the motors to operate below the maximum allowable linear acceleration.

Description

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application Ser. No. 15 / 934,765, filed March 23, 2018, the entire disclosure of which is hereby incorporated by reference into this application. STATE OF THE ART

[0002] The invention relates to robotic devices and methods, and in particular to a mobile driving unit for transporting a load. Examples are disclosed in US 2018 / 0 072 212 A1, DE 11 2016 006 489 T5, DE 11 2016 007 044 T5, US 2017 / 0 045 545 A1, and US 2010 / 0 179 698 A1.

[0003] Maintaining the stability of a mobile driving unit during movement and stopping is a primary concern in propulsion control. For example, changes in acceleration may introduce the risk of tipping of the driving unit or its load. As another example, changes in direction may introduce the risk of the driving unit partially losing physical contact with the surface on which it is traveling. Example systems and methods for implementing vehicle operating limits to prevent load failure during vehicle teleoperation are disclosed in US 2017 / 0 108 871 A1. This disclosure aims to address one or more of these and other problems in controlling the mobility of a driving unit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view illustrating an articulated chassis configuration of a mobile driving unit for which acceleration controls may be implemented; Fig. 2 is a perspective view of a mobile driving unit with a cargo enclosure for which acceleration controls can be implemented; Fig. 3 is a side view of a mobile driving unit illustrating suspension and ballasts for increased stability and traction of the mobile driving unit; Fig. 4A is a bottom view of a mobile travel unit showing rollers oriented for forward movement; Fig. 4B is a bottom view of a mobile carriage unit showing rollers aligned to rotate the mobile carriage unit; Fig. 5 is a schematic diagram of a motion control system of a mobile driving unit; Fig. 6 is a flowchart of an exemplary method of loading linear acceleration controls; and Fig. 7 is a flowchart of an exemplary method for controlling angular acceleration. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0004] A mobile driving unit (“MFE”) 10 includes a chassis assembly 12 of a vehicle, such as an autonomous or semi-autonomous robot, that supports a cargo enclosure 14 that can carry a container (or other cargo) in a logistics center.

[0005] Referring to the Fig. 1 to 2, the chassis 12 is a split chassis including a front chassis unit and a rear chassis unit that are pivoted together so that the front and / or rear chassis can move about a pivot when encountering a ground irregularity. The pivoting feature of the chassis 12 allows the overall height of the mobile driving unit to be reduced compared to previous generations of similar robots.

[0006] The chassis 12 of the mobile traveling unit 10 includes a first chassis assembly such as the front chassis assembly or unit 20 and a second chassis assembly such as the rear chassis assembly or unit 60. The front chassis assembly 20 includes a base 22, a pair of motorized wheel assemblies 24L and 24R, and a front roller 26. The base 22, in the embodiment shown in the figures, is a one-piece aluminum casting to which the wheel assemblies 24L and 24R and the front roller 26 are mounted. The base 22 includes brackets and cutouts for receiving the wheel assemblies 24L and 24R, as well as a recess for mounting the front roller 26. The base 22 also includes a pair of pivot brackets 70, as explained in more detail below.

[0007] The rear chassis assembly 60 includes a base 62 and a rear roller 66. The base 62 is preferably a one-piece aluminum casting that includes a recess for mounting the rear roller 66 and a recess and bracket 74 for a ballast 94. The base 62 may also include a bracket 58 for batteries.

[0008] A pair of pins 68 connect arms to allow the front base 22 and the rear base 62 to pivot relative to each other. The pins 68 define a chassis pivot axis SA about which the bases 22 and 62 pivot or rotate as needed. The axis SA is horizontal and transverse. The axis SA is also perpendicular to a forward direction of travel, which in Fig. 1 is represented by line ML, since in the embodiment shown, the direction of forward movement is parallel to the centerline ML of the MFE 10. The centerline ML bisects the bases 20 and 60 and is equidistant between the drive wheel assemblies 24L and 24R.

[0009] The front rollers 26 and 66 are mounted on the base 22 and 62, respectively - the rollers extend through the base and are secured with bolts 72. Preferably, the rollers 26 and 66 are conventional and may include double wheels. The rollers 26 and 66 pivot freely about the vertical axis through the shafts and are not driven. In the Fig. 2, the rollers 26 and 66 are offset laterally from the center line ML. For example, Fig. 2, the front roller 26, which is spaced to the left of the centerline ML, and the rear roller 26, which is spaced to the right of the centerline ML. The offset spacing allows the travel unit 8 to travel over a measurement mark, such as a barcode or a 3D code, in the floor without any of the wheels 40 or rollers 26, 66 touching the mark. Thus, the centerline ML of the MFE 10 passes directly over a measurement mark when the unit 10 moves forward.

[0010] Each wheel assembly 24L and 24R includes a conventional motor 42L and 42R (as understood by persons familiar with the technology of the mobile traveling unit) and a drive wheel 40L and 40R, respectively. The wheels 40L and 40R are located approximately in the center (in front and behind) of the mobile traveling unit 10. Each wheel 40L and 40R can be driven according to control signals to move the unit 10 forward, or a direction of one of the wheels 40 can be reversed so that the traveling unit 10 can rotate in place by a motion control system 500 (or "control system 500") ( Fig. 5).

[0011] As in Fig. 1, a pair of spring assemblies 80 function to transmit a downward force to each of the front roller 26 and the rear roller 66, and thus the spring assemblies 80 reduce the downward force on the drive wheels 40L and 40R. Each spring assembly 80 includes a retainer 82 attached to a rear portion of the front chassis base 22 and extending rearward to a front portion of the rear chassis base 62.

[0012] Each of the front base 22 and the rear base 62 includes a support structure 98 ( Fig. 2) or brackets 99 for mounting a support structure 98, as explained below and in Fig. 1 shown schematically.

[0013] The support structure 98 may support a cargo enclosure 14. The cargo enclosure 14 may include any structure. Accordingly, the support structure 98 may be of any configuration and is shown only for illustration purposes, as those familiar with mobile driving unit technology will understand and be able to implement, depending on the particular parameters of the application. Various embodiments of the cargo enclosure 14 are discussed in more detail below.

[0014] The brackets 99 may have any configuration and supports connected to the brackets 99 may have any configuration, since the brackets 99 generally include (without limitation) pivot pins and a fixed structure. For example, Fig. 1 illustrates an embodiment in which the front brackets 99F fixedly connect the front support structure 98F to the unit 22, and the rear brackets 99R pivotally connect the rear brackets 99R to the unit 62. In other embodiments, the front brackets 99F may be pivots and the rear brackets may be fixed. Incorporating a pivot bracket allows a structure supported by the support structure 98 to remain horizontally stable regardless of whether the units 22 and 62 are not level with respect to themselves. That is, while the unit 62 adjusts vertically to accommodate irregularities in the driving surface, the pivot bracket 99R can adjust accordingly.

[0015] It may be desirable to maintain the horizontal stability of an upper surface 102 of the cargo enclosure 14 despite the relative vertical movement of the units 22 and 62 as the mobile traveling unit 10 traverses uneven surfaces. Fig. 1 shows support structures 98 pivotally connected to the cargo enclosure 14 via pivot pins 106. For example, each support structure 98 includes two pivot mounts 106. During use, the pivot connections 106 may cooperate with the pivot mount 99R to allow the support structures 98 to move relative to the mobile traveling unit 10 and the cargo enclosure 14. These pivot mounts 98 do not constrain the upper surface 102 of the cargo enclosure 14 to remain in a plane parallel to either the unit 22 or 62, but rather allow the upper surface 102 of the cargo enclosure 14 to remain horizontally planar, or at least more horizontally planar than the unit 22 or 62.

[0016] As discussed above, the support structure 98 supports the load enclosure 14. The load enclosure 14, in turn, may support various components for securing, holding, or moving a load. For example, the load enclosure 14 includes a conveyor assembly 108 that includes a conveyor motor 114 that can be used to move a load. The load may be located on the top surface 102 of the load enclosure 14. The load enclosure 14 may include one or more walls 104 that rise above the top surface 102. For example, Fig. 1 the cargo enclosure 14 with two walls 104, one on each side of the cargo enclosure 14. During use, such frames 104 reduce the likelihood of the cargo bouncing or sliding off the sides of the upper surface 102 despite any shocks or vibrations caused by uneven driving surfaces.

[0017] In some embodiments, the cargo enclosure 14 may include one or more sensors 106 that detect the presence, location, or movement of a load on the top surface 102. For example, such sensors 106 may include sensors integrated into the top surface 102. These sensors may be used to determine the weight or mass of a load. As discussed in more detail below, this information may be used to control the movement of the mobile driving unit 10.

[0018] The mobile driving unit 10 may include one or more mechanical and / or electrical components for increasing or maintaining the stability of the mobile driving unit 10 (including any cargo). For example, as shown in Fig. As shown in Figure 3, the mobile driving unit 10 may include a compression spring 310 that may transfer weight from the wheels 40 to the rollers 26 and 46 to improve driving stability. This may include, for example, transferring weight to one or both of the rollers 26, 46.

[0019] Additionally, the mobile driving unit 10 may include one or more mechanical and / or electrical components for increasing or maintaining the traction of the wheels 40 and / or rollers 26 and 46 along a surface on which the mobile driving unit 10 moves. For example, Fig. 3 the chassis 12, which carries a ballast 320 above the rear roller 66. This additional weight may be detrimental to the speed of the mobile driving unit 10, but may be advantageous in certain environments where, for example, the front of the chassis 12 is otherwise heavier (or carries more of the weight of the load), which could increase the risk of the roller 66 losing traction with the ground surface. Depending on specific implementations and uses of mobile driving units 10, it may be advantageous, in addition to or instead of the Fig. 3 to integrate a ballast 320 above the front roller 26.

[0020] A loss of traction may also occur as a result of the rotation of the mobile traveling unit 10, based on the tendency of the rollers 26, 66 to point in the direction of travel. During forward movement, the rollers 26, 66 are aligned parallel to the wheel assemblies 24L, 24R and the line ML, as shown in Fig. 4A. As the mobile driving unit 10 changes direction, the orientation of the rollers 26, 66 also changes. Fig. Figure 4B shows the rollers 26, 66 not aligned with the line ML, which may be the result of a left turn of the mobile driving unit 10. The distance (or time) required for the rollers 26, 66 to realign with the direction of travel poses a risk of the rollers 26, 66 losing traction. The control system 500 may be used to control the movement to account for this risk, for example, by reducing the acceleration for a sufficient period of time to allow the rollers 26, 66 to reach the direction of travel.

[0021] Fig. 5 is a schematic representation of the control system 500. The control system 500 includes a processor 510 and a memory 520 that stores instructions that cause the controller to perform operations. Such operations are discussed in more detail below. The control system 500 also includes an input / output 530 for receiving and transmitting data. For example, the control system 500 communicates with the motors 42 to control their movement and with the sensor 106 to receive sensor data. The control system 500 may also communicate with, or be part of, other control systems of the mobile driving unit 10.

[0022] The control system 500 can control the movement of the mobile traveling unit 10. The control system 500 enables the mobile traveling unit 10 to perform at least the following movements: move forward, move backward, turn 90 degrees left, turn 90 degrees right, turn 180 degrees, and stop. The control system 500 also performs additional operations to reduce the likelihood that any of the above movements will cause the mobile traveling unit 10 and / or its load to lose stability. Stability can be defined as the load maintaining full contact with the top surface 102 (e.g., no tipping or bouncing) and the wheels 40 and rollers 26 maintaining full contact with a ground surface along which the mobile traveling unit 10 travels, such that the rollers 26 rotate smoothly with the wheels 40 rather than slipping, bouncing, or jumping.

[0023] The stability maintenance operations include loading linear acceleration controls and angular acceleration controls. Loading linear acceleration controls are used to adjust the acceleration for the mobile traveling unit 10 while it is carrying a load (e.g., while loaded) to increase the likelihood of load stability while the mobile traveling unit 10 is accelerating. Angular acceleration controls—which can be used whether the mobile traveling unit 10 is loaded or not—are used to allow the rollers 26 to realign with the direction of travel of the mobile traveling unit 10. Either type of acceleration control can be implemented on the same mobile traveling unit 10, while other mobile traveling units can implement one or the other, depending on the particular usage requirements of the traveling unit.

[0024] The acceleration controls are used by the control system 500 to change motion parameters on the fly. The control system 500 or another system of the mobile driving unit 10 generally uses motion parameters to control the motion of the mobile driving unit 10. Such parameters may include default settings such as a default acceleration (e.g., a linear acceleration value and an angular acceleration value) and speed parameters. Motion parameters may also include trip-specific instructions, such as an instruction for the mobile driving unit 10 to travel to a specific destination or take a specific route. Under certain circumstances, it may be sufficient for the mobile driving unit 10 to consider only basic motion parameters (e.g., destination, maximum speed) to complete a trip.However, it may be appropriate to modify or change these motion parameters through the acceleration controls to increase the likelihood of successfully completing a run.

[0025] Loading linear acceleration controls limit the maximum acceleration of the mobile driving unit 10 depending on the mass of the load. For heavier loads, the acceleration limits are controlled by the need for driving stability of the mobile driving unit 10. For lighter loads (which thus exert less downward force on the mobile driving unit 10), the risk of load instability defines the acceleration limits. This limited acceleration can be the permissible maximum linear acceleration or the acceleration upper limit. This acceleration upper limit can apply to the linear movement of the mobile driving unit 10. Loads with a mass below a certain limit can have the same acceleration upper limit set by the default parameters because the risk of load tipping is higher.As the cargo mass increases, the acceleration limit may decrease because the risk of the cargo tipping may decrease based on the mass of the cargo.

[0026] Fig. 6 is a flowchart illustrating a method 600 that may be performed by the control system 500 to implement loading linear acceleration controls. In step 610, the control system 500 determines a mass of a load of the mobile driving unit 10. This may include receiving data from the sensor 106. Additionally or alternatively, step 610 includes receiving data from an external source, such as a control center that manages a fleet of mobile driving units 10.

[0027] In step 620, the control system 500 calculates an upper acceleration limit based on a value of the mass. This calculation may take into account various attributes of the mobile vehicle 10 and / or its cargo, including the coefficient of friction between the upper surface 102 of the mobile vehicle 10 and the cargo of the mobile vehicle 10; the center of gravity of the mobile vehicle 10, its cargo, or the combination thereof; any straps or belts securing the cargo to the mobile vehicle 10; the fragility of the cargo contents; the speed of the mobile vehicle 10; or other factors or attributes.

[0028] For example, for one embodiment, the acceleration limit of the mobile driving unit 10 does not change until the cargo mass reaches a certain threshold. Specifically, for the mobile driving unit 10, the acceleration limit is 1.3 meters per second squared until the cargo mass is approximately 272 kilograms. When the cargo mass is between approximately 272 kilograms and 544 kilograms, the acceleration limit (measured in meters per second squared) is calculated according to the following equation, where the mass is equal to the mass of the cargo measured in kilograms: linear acceleration=1.7ms2−0.00147ms2kg×mass

[0029] According to this equation, if the mass does not exceed 340 kilograms, the acceleration limit does not exceed approximately 1.2 meters per second squared. If the mass does not exceed 408 kilograms, the acceleration limit does not exceed approximately 1.1 meters per second squared. If the mass does not exceed 475 kilograms, the acceleration limit does not exceed approximately 1.0 meters per second squared.

[0030] Note above that the measurements—both of the cargo mass and the acceleration ceiling—are all approximate values. These approximations are used to account for minute differences in acceleration and / or mass that have a negligible impact on cargo stability. Furthermore, other factors, such as the coefficient of friction between the cargo and the upper surface 102 and others discussed above, can shift the values within ten percent.

[0031] In other embodiments, the acceleration limit does not exceed 1.5 meters per second squared when the mass is less than about 270 kilograms. As another example, the acceleration limit does not exceed 1.4 meters per second squared when the mass is less than about 340 kilograms. As another example, the acceleration limit does not exceed 1.2 meters per second squared when the mass is less than about 400 kilograms. As another example, the acceleration limit does not exceed 1 meter per second squared when the mass is less than about 475 kilograms.

[0032] In step 630, the control system 500 receives an instruction to operate the mobile driving unit 10. Such instructions may include or indicate a command to move the mobile driving unit 10 forward or backward. In step 640, the control system 500 controls the movement of the mobile driving unit 10 to prevent the linear acceleration of the mobile driving unit 10 from exceeding the acceleration limit. In some circumstances, this may include making no adjustments to the command received in step 630, for example, if the command, left unchanged, would not cause the acceleration to exceed the acceleration limit. In other circumstances, step 640 may include modifying the command received in step 630. Such a modification may simply be to limit the maximum acceleration of the mobile driving unit 10 to the acceleration limit.Other modifications may include applying a multiplier to an acceleration profile specified by the instruction received in step 630 (e.g., decreasing all acceleration values by 10%) to prevent the maximum acceleration from exceeding the acceleration cap.

[0033] Instability can also occur when rotating the mobile driving unit 10. The rollers 26 are passive components whose direction and movement are determined by the movement of the motorcycle assemblies. When the mobile driving unit 10 changes direction (e.g., makes a ninety-degree turn), there is a slight delay before the rollers 26 align with the new direction of travel, increasing the risk of slipping. By accounting for the directional differences in a previous movement and the next movement of the mobile driving unit 10, adjustments to the angular acceleration can be made to allow the rollers 26 to be properly aligned with the direction of travel without slipping.

[0034] Fig. 7 is a flowchart of a method 700 for implementing angular acceleration controls to enable roller alignment. In step 710, the control system 500 determines a previous directional movement of the mobile traveling unit 10. In step 720, the control system 500 determines a next directional movement of the mobile traveling unit 10. Although these steps are stated separately, they may occur either in order or concurrently; that is, the control system 500 may determine a comparison of the previous directional movement and the next directional movement. The previous directional movement indicates a direction of the front roller 26 and the rear roller 26. See, for example, Fig. 4B. For example, if the mobile driving unit 10 has just completed a left turn, the roller 26 still points in that left direction and the roller 66 still points in the right direction. If the mobile driving unit 10 has just completed a right turn, the roller 26 still points in the right direction and the roller 66 still points in the left direction. If the mobile driving unit 10 is only moving forward or backward, the rollers 26 still point forward or backward, respectively.

[0035] In cases where the next directional movement occurs in the same direction as the previous directional movement, the angular acceleration may not need to be adjusted during the next directional movement because the rollers 26 are already aligned in that direction. However, if the previous directional movement differs from the next directional movement, depending on this difference, the angular acceleration may be reduced for a certain period of time (certain number of degrees or distance traveled) to allow the rollers 26 to align.

[0036] In step 730, the control system 500 determines a maximum allowable angular acceleration and a maneuvering angle based on the previous and next directional movements. The maximum allowable angular acceleration may be determined as a function of a default angular acceleration value; that is, the maximum allowable angular acceleration may be a reduced angular acceleration of the default angular acceleration. For example, if the previous directional movement and the next directional movement are the same, the maximum angular acceleration value may be the default angular acceleration value.If the previous directional movement was a rotation and the next directional movement is something other than a rotation in the same direction as the previous directional movement, the maximum angular acceleration value can be reduced by an acceleration reduction factor of 0.5, so that the maximum acceleration can be equal to 50% (or 0.5%) of the default angular acceleration value.

[0037] The previous and next directional movements also affect the maneuvering angle, i.e. the angle for which the angular acceleration is reduced to reduce the risk of slipping when the rollers 26, 66 align with the direction of travel. The maneuvering angle 6 is in Fig. 4B. The greater the difference between the roller direction (indicated by the previous directional movement) and the direction of the next directional movement, the greater the maneuvering angle. This gives the mobile driving unit 10 more time (and angular distance) for its rollers 26 to properly align.

[0038] If the previous directional movement and the next directional movement are turns in the same direction, the maneuvering angle is zero (0) degrees. If the previous directional movement is a first turn in one direction and the next directional movement is a second turn in an opposite direction, i.e., if the mobile driving unit makes a left turn after completing a right turn or makes a right turn after completing a left turn, the maneuvering angle is twenty (20) degrees. If the previous movement is linear—either forward or backward—and the second movement is a turn, the maneuvering angle is ten (10) degrees, as in Fig. 4B shown.

[0039] In step 740, the control system 500 causes the mobile vehicle 10 making a turn to limit its angular acceleration for at least the maneuvering angle based on the allowable maximum angular acceleration. For example, if the mobile vehicle 10 performs a ninety (90) degree turn after traveling forward, the control system 500 limits its angular acceleration to fifty percent (50%) of the default angular acceleration value for the first ten (10) degrees of the turn. In some embodiments, after these ten degrees are reached, the control system 500 allows the mobile vehicle 10 to complete the remaining eighty (80) degrees of the turn at the default angular acceleration value.

[0040] The mobile driving unit includes controllers, cameras and other sensors, a docking connector, a turntable, motors for raising and rotating the turntable, and the other components. A person familiar with mobile driving unit technology will understand how to assemble and use the additional components on the front and rear chassis units disclosed herein in accordance with the particular objectives and design of the mobile driving unit application.

[0041] The present invention has been described by illustrating certain features with reference to a particular embodiment. For non-limiting example only, components are referred to as front and rear to illustrate 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 a problem described herein, unless expressly stated in the claims. Nor is the invention in any way limited to embodying an advantage unless expressly stated in the claims. Rather, the structure and function described herein are merely illustrative, and the claims are intended to be given their full scope.

Claims

[1] Mobile driving unit with a linear acceleration value and an angular acceleration value, the mobile driving unit comprising: a chassis assembly having a pair of drive wheel assemblies, each drive wheel assembly including a motor; a front and a rear roller, each connected to the chassis assembly; a support structure mounted on the chassis assembly; a cargo enclosure mounted to the support structure, the cargo enclosure including a top surface; a controller communicatively connected to the drive wheel assemblies of the center chassis; and a memory that stores instructions that cause the controller to perform operations, the operations including: Determining a mass of a charge located on the upper surface; Defining a permissible maximum linear acceleration based on the linear acceleration value and the mass of the load; Determining a previous directional movement of the mobile driving unit, the previous directional movement indicating a direction of the front roller and the rear roller; Determining a next directional movement of the mobile driving unit which is different from the previous directional movement; Defining a maximum allowable angular acceleration and maneuvering angle based on the previous directional movement and the next directional movement, such that the maximum allowable angular acceleration is lower than a standard acceleration value for a given number of degrees or distance traveled to align the direction of the front roller and the rear roller; if the next directional movement involves a turn, causing the motors to operate at the maximum permissible angular acceleration for at least the maneuvering angle; and if the next directional movement involves a linear movement, causing the motors to operate below the maximum allowable linear acceleration. [2] The mobile driving unit of claim 1, wherein the allowable maximum angular acceleration is fifty percent (50%) of the angular acceleration value. [3] A mobile driving unit according to claim 1, wherein the previous directional movement is a first rotation and the next directional movement is a second rotation in an opposite direction to the first rotation. [4] A mobile driving unit according to claim 3, wherein the maneuvering angle is twenty (20) degrees. [5] The mobile driving unit of claim 1, wherein the previous directional movement is linear, the maneuvering angle is ten (10) degrees. [6] The mobile driving unit of claim 1, wherein the cargo enclosure includes a sensor and determining the mass is based on receiving data from the sensor. [7] Mobile driving unit according to claim 1, wherein the permissible maximum linear acceleration is equal to the linear acceleration value when the mass does not exceed 270 kilograms. [8] Motion control system for a mobile driving unit comprising: a chassis assembly having a pair of drive wheel assemblies, each drive wheel assembly including a motor; a front and a rear roller, each connected to the chassis assembly; a support structure mounted on the chassis assembly; a cargo enclosure mounted to the support structure, the cargo enclosure including a top surface, the motion control system comprising: a processor; and a memory that stores instructions that cause the processor to perform operations, the operations including: Determining a mass of a charge located on the upper surface; Defining a permissible maximum linear acceleration based on the linear acceleration value and the mass of the load; Determining a previous directional movement of the mobile driving unit, the previous directional movement indicating a direction of the front roller and the rear roller; Determining a next directional movement of the mobile driving unit which is different from the previous directional movement; Defining a maximum allowable angular acceleration and maneuvering angle based on the previous directional movement and the next directional movement, such that the maximum allowable angular acceleration is lower than a standard acceleration value for a given number of degrees or distance traveled to align the direction of the front roller and the rear roller; if the next directional movement involves a turn, causing the motors to operate at the maximum permissible angular acceleration for at least the maneuvering angle; and if the next directional movement involves a linear movement, causing the motors to operate below the maximum allowable linear acceleration. [9] A motion control system according to claim 8, wherein determining the mass is based on data transmitted from a sensor integrated in the mobile driving unit. [10] The motion control system of claim 8, wherein the mass is measured in kilograms and the maximum linear acceleration, measured in meters per second squared, is approximately equal to 1.7 minus the mass multiplied by 0.00147 meters per kilogram per second squared. [11] The motion control system of claim 8, wherein the maximum linear acceleration does not exceed 1.5 meters per second squared when the mass is less than about 270 kilograms. [12] The motion control system of claim 8, wherein the maximum linear acceleration does not exceed 1.4 meters per second squared when the mass is less than about 340 kilograms. [13] The motion control system of claim 8, wherein the maximum linear acceleration does not exceed 1.2 meters per second squared when the mass is less than about 400 kilograms. [14] The motion control system of claim 8, wherein the maximum linear acceleration does not exceed 1 meter per second squared when the mass is less than about 475 kilograms.

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