Work machine with force input control of traction drive

Abstract

A walk-behind work machine includes an electric traction drive operable to move the work machine. An input sensor detects force applied to or movement of a handle of the work machine by an operator and provides a control signal in response thereto. The control signal used to affect a speed of the electric traction drive. A controller is operable to provide control of the electric traction drive. The controller adjusts control variables (e.g., control input values, control parameters) in response to measured data such as zero-force signals of the force sensor and mode selections by the operator.

Description

PATENTDocket No. 0206.000346W001 (P01942-W001)WORK MACHINE WITH FORCE INPUT CONTROL OF TRACTION DRIVERELATED PATENT DOCUMENTS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 667,883, filed on July 5, 2024, U.S. Provisional Application No. 63 / 676,725, filed on July 29, 2024, and U.S. Provisional Application No. 63 / 750,187, filed on January 27, 2025, all of which are incorporated herein by reference in their entireties.SUMMARY

[0002] The present disclosure is directed to work machine platforms such as mowers, snow-throwers, aerators, trenchers, edgers, and the like. In one embodiment, a walk-behind work machine includes an electric traction drive operable to move / propel the work machine. The work machine includes an input sensor that detects force applied to or movement of a handle of the work machine by an operator and provides a control signal in response thereto, the control signal used to affect a speed of the electric traction drive. The work machine includes a lockout control that activates or deactivates motion of the work machine. A controller is operable to provide control of the electric traction drive. The controller is further operable to measure a zero-force value of the control signal before the lockout control is set to activate the traction control and adjust subsequent values of the control signal by the zero-force value when the traction control is activated and the operator is applies force to the input sensor to move the work machine.

[0003] In another embodiment, a walk-behind work machine includes an electric traction drive operable to move the work machine. The work machine includes an input sensor that detects force applied to or movement of a handle of the work machine by an operator and provides a control signal in response thereto, the control signal used to affect a speed of the electric traction drive. The work machine includes mode control input device that accepts operator input to change a mode of the work machine. The work machine includes a controller operable to provide control of the electric traction drive. The controller is further operable to determine the mode of the work machine being changedPATENTDocket No. 0206.000346W001 (P01942-W001) via the mode control input device, adjust a coefficient of the closed-loop controller in response to the changed mode.[00041 In another embodiment, a walk-behind work machine includes a traction drive operable to move the work machine. A traction speed of the traction drive is variable in response to a mechanical input to the traction drive. A handle extends from the work machine to allow an operator to guide the work machine during its movement. A handle grip slides on the handle in response to operator-applied forces in respective pulling and pushing directions. The sliding of the handle grip changes the mechanical input and thereby respectively decreases and increases the ground speed of the walk behind work machine. The machine includes an adjustable maximum speed limiting means that selectably limits the relative movement of the grip in the pushing direction relative to the handle.

[0005] These and other features and aspects of various embodiments may be understood in view of the following detailed discussion and accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The discussion below makes reference to the following figures, wherein the same reference number may be used to identify the similar / same component in multiple figures. The drawings are not necessarily to scale.

[0007] FIG. l is a perspective view of a walk-behind work / utility machine according to an example embodiment;

[0008] FIG. 2A is a block diagram of a control system according to an example embodiment;

[0009] FIG. 2B is a view of a mode selector switch according to an example embodiment;

[0010] FIGS. 3 and 4 are block diagrams of closed-loop controllers according to various embodiments;

[0011] FIGS. 5, 6, and 7 are flowcharts of methods according to example embodiments; andPATENTDocket No. 0206.000346W001 (P01942-W001)

[0012] FIGS. 8-12 are diagrams showing a mechanical implementation of speed control modes according to various embodiments.DETAILED DESCRIPTION

[0013] In the following detailed description of illustrative embodiments, reference is made to the accompanying figures of the drawing which form a part hereof. It is to be understood that other equivalent embodiments, which may not be described and / or illustrated herein, are also contemplated.

[0014] Walk-behind grounds maintenance machines include mowers used by homeowners to maintain their yards and grounds. Other walk-behind work machines include, among other things, snow-throwers, aerators, edgers, trenchers, trimmers, tractors, and forklifts. Such machines have a frame that carries various wheels or tracks for allowing movement of the frame over the ground. These work machines are typically provided with one or more work implements, such as mower blades, snow throwing augers, etc. Some machines, such as walk behind tractors, may include a generic interface that allows interchanging a number of different work implements. In embodiments described herein, the work machine has a traction drive to self-propel the work machine over the ground while being guided by an operator that walks behind the machine.

[0015] In embodiments described herein, an electric motor powered by an onboard battery pack is mounted on the frame of the work machine. The power source is at least coupled to the traction drive to rotate at least some of the wheels carried on the frame, and may also be coupled to the work implement, e.g., a mower cutting blade in a horizontal cutting plane. The traction drive relieves the operator of having to manually propel (e.g., push) the frame over the ground.

[0016] The frame of the machine typically includes an upwardly and rearwardly extending handle to allow the operator to guide the frame during a work operation. Various hand operated operational controls are typically located on the upper end of the handle. Such controls allow the operator to engage and disengage the work implement and / or to engage and disengage the operation of the traction drive. When the traction drive isPATENTDocket No. 0206.000346W001 (P01942-W001) capable of propelling the mower at a variable ground speed, such controls will also allow the operator to affect the ground speed, e.g., cause to mower to move at a pace desirable to the operator.

[0017] For example, some internal combustion engine (ICE) powered walk behind mowers use a variable ground speed control that varies the slip in a belt drive transmission in proportion to a force on the handle exerted by the operator. In this way, the operator can vary a speed of the mower by increasing or decreasing a force applied to the handle. This feature has shown to be desirable, and so a similar feature is equally desirable for electrically driven mowers and other walk behind machines.

[0018] One advantage of electric drive machines is that they often don’t require transmissions and other mechanical linkages for operation and control. Motor controllers provide a high degree of control over motor speed and power and can be configured and operated in a number of ways. For example, a data interface for a motor controller can accept signals from relatively compact, inexpensive, and reliable devices, such as physical input devices (e.g., switches, potentiometers), remote data interfaces (e.g., wireless interfaces), sensors, etc. These devices can be coupled to the controller via wires or other data communication media, which are also compact and relatively inexpensive.

[0019] While it may be relatively inexpensive to add new capabilities to electrically driven work machines, it is not always so simple to achieve the desired behaviors of those machines. This can be the case for electrical controls that replace familiar mechanical controls. For example, in vehicle applications, the use of electrically assisted power steering is often seen as a negative compared to hydraulically assisted steering, because the electric assist often provides less steering feedback to the driver.

[0020] Both mechanical and electrical controls can exhibit changes in performance over time that affect the usability of a work machine. Mechanical changes are often easy to predict and correct, e.g., adjustment of control cables, lubrication of joints, etc. While electrical controls have been proven to be reliable in many applications, the sensors and data communications channels that communicate sensor signals have non-ideal characteristics (e.g., noise, non-linear behavior) that need to be dealt in order to ensure predictable and reliable operation in real-world conditions. These non-ideal characteristicsPATENTDocket No. 0206.000346W001 (P01942-W001) can also change over time and so the electronic control logic should implement measures should be able to compensate for still-functional components that are no longer performing to factory specifications.

[0021] While the devices, systems, and methods described below may be implemented in any type of walk behind work vehicle, electric rotary mowers will be used to illustrate the various concepts. In FIG. 1, a perspective view shows a walk behind mower 100 according to an example embodiment. The mower 100 includes a frame 102, which is often referred to as a deck for mowers. The frame 102 provides mechanical support for the various units of the mower 100, such as a traction unit has an electric motor that rotates drive wheels 104. A work implement (e.g., a cutting blade, not shown) is coupled to the same or different motor that provides traction. A battery pack 106 provides onboard electric power for the mower 100.

[0022] A handle 108 provides user physical control of the mower 100, e g., for pushing, pulling, and steering. A grip end 109 of the handle 108 includes user controls, such as a start button / switch 110 and blade control levers 112. The blade control levers 112 are spring-loaded levers members that activate on-off switches, and the cutting blade will not turn until at least one of the levers 112 squeezed by the operator. This is sometimes referred to as an “operator presence control” or “dead man’s switch,” and may take other forms than the illustrated levers 112. For example, a spring-loaded, U-shaped bar (sometimes referred to as a “bail”) can perform a similar function as levers 112.

[0023] In order to propel the mower 100, a force sensor is located somewhere between the operator / user (not shown) and the frame 102, which may include a location on the handle 108 and / or a coupling location between the handle 108 and the frame 102. Circles 114-116 are representative of possible force sensor locations, and multiple sensors may be made at corresponding locations on both sides of the mower (e.g., left and right side of handle 108). While the term force sensor is used herein, other types of sensors such as pressure sensors and displacement sensors may be used to derive an applied force between the handle 108 and the frame 102. The force sensor may be operable to detect one or both of compressive forces (pushing the handle 106 forward) and tensile forces (pulling the handle 105 rearward).PATENTDocket No. 0206.000346W001 (P01942-W001)

[0024] In FIG. 2A, a block diagram shows a work vehicle traction control system 200 according to an example embodiment. An input sensor 202 provides a control signal 203 indicative of an operator pushing and / or pulling on a handle of the mower. The input sensor 202 may include one or more of a piezo sensor, strain gauge, resistive sensor, and the like. The input sensor 202 may be in some cases be implemented as or with a pressure sensor, in which the force over an area is measured. The input sensor 202 may in some cases be implemented as a movement, displacement, or strain sensor, which measures a deformation or movement of a structure having a known stiffness in the direction of deformation or movement that is used to derive a value indicative of force. Generally, these may be referred to as variable input sensors, as they allow varying some aspect of the vehicle’s operation based on a variable force applied to or movement of the sensor.

[0025] The speed signal 203 is input to a traction control circuit 204, which may include a number of different electronic subsystems. For example, the signal 203 may be processed by analog and digital signal processing elements of the traction control circuit 204, e.g. filters, preamplifiers, analog-to-digital converters (ADC), digital-to-analog converters ((DAC), etc. In some embodiments, signal processing circuits may be included on the sensor 202, such that the control signal 203 is a digital message sent over a communications bus, e.g., controller area network (CAN), inter-integrated circuit (I2C), etc. The traction control circuit 204 may also include a control circuit, e.g., an open-loop controller, closed-loop controller. Operations of the system 200 may be governed by a system controller (not shown) such as a system on a chip (SoC) that generally governs operations of the mower by executing software or firmware instructions. In some embodiment, the traction control circuit 204 may be integral with a system controller.

[0026] The traction control circuit 204 also includes or is coupled to motor control circuits that output one or more drive signals 205 to control one or more motors 206. The drive signals 205 may include one or both of electrical power (e.g., to energize motor coils) and data signals (e.g., analog and / or digital signals) to control the motor 206, e.g., to vary motor speed, motor torque, input current, etc. The motor 206 (or a motor-coupled sensor) may also provide signals back to the speed control circuit 204, e.g., sensor readings such as temperature, faults, encoder signals, current draw, etc.PATENTDocket No. 0206.000346W001 (P01942-W001)

[0027] The motor 206 is mechanically coupled (as indicated by dotted lines) to a traction mechanism 208, such as wheels and / or treads. The motor 206 and traction mechanism 208 are engaged to move the mower across the ground based on inputs from the input sensor 202, and optionally at least one other sensor or control input as described below. The movement induced by the traction mechanism 208 is detected by a movement sensor 210, which may detect one or more of vehicle displacement, velocity, acceleration, motor torque, motor current, etc. Generally, a movement signal 211 from the movement sensor can be used as an indicator of speed for using in the traction controller 204, although does not need to directly measure speed, e.g., in the case of motor torque or current. The movement signal 211 can either be used directly or processed via intermediate calculations, e g., integration of an accelerometer output, time average of a wheel encoder.

[0028] As will be described in various scenarios below, the traction control circuits 204 may use inputs provided from other sensors 212 as well as optional user input devices such as work implement activation control 214 (e.g., on / off switch, potentiometer) and mode selection control 216. The mode selection control 216 may include any combination of a mode toggle button, multiple position switch, threshold pressure on input sensor 202, height of cut selector (e.g., dial, toggle switch, potentiometer) or the like. The operator uses the work implement activation control 214 to at least activate and deactivate the work implement as indicated by activation signal 215, The work implement activation control 214 may provide other types of control, such as direction, speed, height of cut, and these control values may also be included in the activation signal 215.

[0029] The mode selection control 216 can change modes of the traction drive and / or work implement via mode signal 217. For example, there are situations where the operator may want a constant speed of the traction drive. In a constant speed mode (or crawl mode), a value of the mode signal 217 will cause the control signals 203 to be ignored or to be used for only stop and go commands without speed being regulated in correspondence with forces applied to the input sensor 202. In other words, regardless of pressure on the input sensor 202 and the speed of machine, the operator could actuate a crawl mode button (see FIG. 2B) and the machine would travel at pre-programmed speed (e.g., 0.1-1 mph). The crawl mode would allow for maneuvering the work machinePATENTDocket No. 0206.000346W001 (P01942-W001) through a transit path (e.g., end of driveway) without the input sensor 202 impacting wheel speed. The crawl mode could also be used to pull the work machine up a slope versus having to physically push the machine handle to cause the input sensor 202 to actuate the traction drive.

[0030] As in FIG. 2B, the mode selection function 216 can be implemented using a multiple position switch 226 in one embodiment. At position 227 of the switch 226, the traction system is shut off. At position 228 of the switch 226, a speed of the work machine is governed by the input sensor 202, e g., forward speed is set proportional to a forward force applied to the input sensor 202. At position 229 of the switch 226, a forward speed of the work machine is governed by the input sensor 202, but through a reduced speed range, as discussed below. At position 230 of the switch 226, a forward speed of the work machine is set to a constant value regardless of inputs the input sensor 202. The constant value of the forward speed in this mode may be set by a second control (not shown) or via multiple positions of switch 226 (e.g., crawl-low, crawl -medium, crawl-high). At position 231 of the switch 226, a forward speed of the work machine is set to a constant value similar to position 230, except that the input sensor 202 can provide proportional braking control, e.g., reduction in forward speed is proportional to a rearward (pulling) force applied to the input sensor 202.

[0031] When switching between modes or other control transitions (e.g., one of the crawl modes being deactivated, handle pressure falling below a threshold in personal pace mode), the traction maximum speed may be reduced. The reduction in maximum traction speed can avoid a sudden unanticipated acceleration of the unit. The reduction of maximum traction speed may be enforced over a predefined time period (e.g., 1 second after a mode change is detected) and may be ramped between from reduced and maximum speeds after the time period has elapsed.

[0032] In reference again to FIG. 2A, the traction control circuits 204 may provide any combination of open loop control and closed-loop control of the motor 206 and traction mechanism 208. Open loop control generally refers to a scheme where a control input is mapped via a transfer function to a control output. An example would be a simple accelerator control that provides an input voltage VA of between 0V and 5 V that is mappedPATENTDocket No. 0206.000346W001 (P01942-W001) to a motor voltage VM between OV and 24V. A linear transfer function of VM = 24 / 5 VA could be used to map the inputs to the outputs.[00331 While an open loop controller is relatively simple to implement, it typically can’t account for changes in the system that occur during operations. One example of this is shown as disturbance 218 in FIG. 2A, which affects the traction mechanism 208. An example of disturbance 218 is wheel slip, which can occur on slippery ground surfaces. Disturbance can affect any part of the traction drive including the motor 206. A disturbance may be mechanical and / or electrical in nature. The latter may include random electrical noise, power supply variations, changes in conductive path resistance, and the like.

[0034] A closed-loop controller uses a feedback signal to measure the actual response of the system to the input. For example, where a constant speed is desired in response to the control signal 203, the movement signal 211 could be used as feedback. Thus, for example, if a disturbance 218 such as a muddy surface is bogging down a drive wheel, this will be reflected in the movement signal 211, and the traction control circuits 204 can increase motor inputs 205 to compensate. In other embodiments, the closed-loop controller may use motor torque as a set point (e.g., the movement sensor 210 may be a torque sensor) and change the inputs 205 to maintain operation within a predetermined torque range. In this latter example, the speed of the work machine may not be a setpoint, but the user control signal 203 will still tend to affect speed of the work machine even if speed is not directly measured or considered in the control scheme.

[0035] A robust closed-loop controller algorithm that may be used by the traction control circuits 204 is known as proportional-integral-differential (PID). An example of a PID controller usable in a walk behind work machine traction controller is shown in the diagram of FIG. 3. The PID controller in this example controls an operational state of a plant, in this case the plant being the motor 206 and traction mechanism 208, and may also include power delivery circuitry in the traction controller 204. The state being controlled by the PID controller includes a characteristic of the mower’s traction system such as speed, torque, motor current, etc. A sensor provides a feedback signal indicative of a realtime state of the plant. In this case the feedback signal is the movement signal 211 from thePATENTDocket No. 0206.000346W001 (P01942-W001) one or more movement sensors 210. If the feedback signal is motor current, it may be obtained by a component that drives the motor 206, such as a motor power component that provides drive power 205 shown in FIG. 2A.

[0036] At summation block 300, the movement signal 211 is compared with a set point of the plant, in this case the control signal 203 from the input sensor 202. Note that there will likely be a transformation of one or both of the movement signal 211 and the control signal 203 so that they can be compared. In this example, transform function block 301 can be used to transform or scale the control signal 203 to provide a transformed control signal 303 that is combined with the movement signal 211. In particular, the movement signal 211 is subtracted from the transformed control signal 303 to obtain an error signal 302. The error signal 302 represents a deviation of the plant from the desired set point and is used by one or more blocks 304-306 to correct for the deviation, the blocks 304-306 being collectively referred to as PID control block 308.

[0037] Block 304 provides an output 308 proportional to the error signal 302, and the influence of the proportional correction (P) is set by the coefficient Kp. For purposes of this disclosure, the term “proportional to” does not imply or require a linear relationship, but merely indicates that an increase in an input causes an increase in an output, and that a decrease in the input causes a decrease in the output. Similarly, the term “in inverse proportion to” would at most indicate that an increase in the input causes a decrease in the output, and vice versa. Block 305 provides an output 309 based on an integration of the error signal 302, and the influence of the integral (I) is set by the coefficient Ki, as well as a time (e.g., a number of discrete samples) over which the error signal is integrated. Block 306 provides an output 310 proportional to the time derivative of the error signal 302, and the influence of the differential correction (D) is set by the coefficient KD. Any of the correction values derived in the blocks 304-306 can be removed from consideration by setting the appropriate coefficient to zero. For example, in a system where fast response is not required or desired (e g., may cause instability), the value of KD may be set to zero, in which case only the output of blocks 304 and 305 would be evaluated in in the summation block 311, an arrangement referred to as a PI controller. The summed output 312 of the PID control block includes data and / or power signals that drive the plant 206, 208.PATENTDocket No. 0206.000346W001 (P01942-W001)

[0038] The coefficients Kp, Ki, and KD can be estimated via physical modeling of the plant, based on measurements of the physical device, or found by trial and error. Generally, once a set of reasonably well-performing coefficients is found, they can be further tuned by testing the work machine under varying conditions, including different users and work conditions. In some cases, a set of coefficients that works well under some conditions, such as when running the work implement (e.g., cutting blade) may not work as well when those conditions have changed (e.g., transport mode only with cutting blade turned off).

[0039] As indicated the arrowhead line extending from the right side of the work implement activation control 214 in FIG. 3, the work implement activation signal 215 can be used to adaptively adjust the PID control block 308. This may involve changing at least one of Kp, Ki, and KD in blocks 304-306 when the implement is switched on or off. Additional adaptations to the PID control block 308 can be made, for example, if the work implement activation control 214 provides more than just on and off control of the work implement. The coefficients can be changed, for example, to adapt for one or more of changing a direction of rotation of the implement, setting of the implement (e.g., cut height), selecting a subset of multiple implements, and changing a speed of the implement.

[0040] Other operator controls can be used to adaptively change a PID control block 308, such as shown in the diagram of FIG. 4. In this case, the mode signal 217 from mode selection control 216 can be used to change one or both of the PID control block 308 and the transform function block 301. For example, the work machine may have a crawl mode, in which the traction control moves within a speed range that is a fraction of its normal speed range. A crawl mode may be useful on machines such as snow throwers or trenchers that are encountering higher than usual loads on the work implements.

[0041] As indicated by the mode signal 217a extending from the right of the mode selection control 216, this changing in and out of crawl mode may involve changing the coefficients Kp, Ki, and KD to account for the different speed ranges of the different modes. As indicated by the mode signal 217b extending from the top of the mode selection control 216, changing in and out of crawl mode may also or instead involve changing the mappingPATENTDocket No. 0206.000346W001 (P01942-W001) of the control signal 203 to the transformed control signal 303 via the transform function 301 to enforce the different speed ranges of the different modes.[00421 Inother embodiments, the crawl mode may just set the work machine to a fixed speed regardless of control signal 203, e.g., at a low end of the first speed range (e.g., 5-30% of maximum speed). This may involve, for example, switching out the transformed control signal 303 with a constant signal. In another embodiment, the transform function 301 may be configured to put out a constant in response to crawl mode being selected via mode selector 216. In this way, the system can still take advantage of the PID control block to maintain the constant set speed, e.g., via closed loop control.

[0043] Another mode that may be made available in a work machine is referred to herein as brake control mode. In this mode, the walk-behind machine will move forward at a constant speed, such that forward inputs indicated by the control signal 203 (e.g., pushing on the handle) will have no effect on speed. However, if the operator applies a reverse force (e.g., pulling on the handle) to the input sensor 202, the control signal 203 will be used to slow the traction drive. In order to implement this, the mode control signal 217 input to the change the transform function to something such as: if force > 0, F() = constant_speed, else F() = constant_speed + force. Since force is negative or zero in the latter part of the expression, the effect will be to reduce the speed. The mode change to brake control mode may also change Kp, Ki, and KD.

[0044] Note that the changing of coefficients shown in FIGS. 3 and 4 may also be applied to an open loop controller. Generally, an open loop controller will produce an output based on a control input and an input-to-output mapping. An open loop controller can be changed based on work implement activation, mode selection, and the like in a number of ways. For example, a multiplier coefficient may be used to change the mapping between input and output. In another example, a different lookup table or transform function could be referenced that provides a different input-to-output mapping. In the latter case, the swapping out of the lookup table or transform could be considered a change in coefficient, e.g., changing a memory pointer to point to a different mapping table or function.PATENTDocket No. 0206.000346W001 (P01942-W001)

[0045] Mode changes that affect machine control may also result in drift in the control signal 203. Oftentimes, the machine will include a lockout switch (e.g., bail or trigger 112 as shown in FIG. 1) that is biased (e.g., spring loaded) such that the machine can only operate when being grasped by the operator. When using an input sensor 202 for speed control, the operator will activate the lockout switch before pushing or pulling on the handle to cause motion. Thus, the lockout switch can be considered part of mode selection control 216.

[0046] In some embodiments, the system can monitor the control signal 203 just before activation of the lockout switch to determine a zero-force signal level that can be used by transform function block 301 to offset the control signal 203 due to zero volt drift of the input sensor 202. For example, if the control signal 203 is supposed to be 0V with no force applied but has been averaging 0.2V for a few seconds before the lockout switch was activated, then this 0.2V value will be subtracted in transform function block 301 to correct any subsequent values of the control signal 203. Since there are many occasions when the operator could intentionally release the lockout switch (e.g., to pause operation to remove large debris from the work path), this measurement and correction of the control signal 203 can occur many times in a work session.

[0047] In FIG. 5, a flowchart shows an example of setting of a zero-force value for an input sensor according to an example embodiment. Block 500 represents an infinite loop entry point, in which block 501 tests whether a lockout control of an electrically driven work machine is activated. If not, then block 502 measures a zero-force value of an input sensor and stores the measured value in a single variable or data structure Zf. The data element Zf may be a single calculated value, e.g., a running average, or may be a data structure such as a linked list or accumulator that stores the last N-measurements (e.g., 10- 20 measurements).

[0048] The blocks 500-502 form a loop that is continuously executed until the lockout control is set to activate the traction, when block 501 returns ‘yes.’ In such an event, block 503 determines a control adjustment value Af based on Zf. The value Af of may be the same as Zf, or block 503 may perform further calculations if Zf is a collection. For example, a statistical analysis may be performed on a collection of zero-forcePATENTDocket No. 0206.000346W001 (P01942-W001) measurements, and outliers (e.g., greater than three times the standard deviation) may be discarded before combining (e.g., averaging) the remaining values.[00491 At block 504, the value of Af is used to adjust a control signal from the input sensor, e.g., subtract from a measured value of the sensor. Blocks 504 and 505 will continuously loop so long as the lockout control is activating traction, such that the same value of is Af used to adjust control inputs. Once the lockout control is released or otherwise deactivates traction, block 505 returns ‘no’ and the process repeats, e.g., measuring 502 the zero force value.

[0050] In FIG. 6, a flowchart shows a method of controlling a work machine in different modes according to an example embodiment. The method involves detecting 600 (e.g., measuring) a control signal in response to forces applied to a handle of a work machine by an operator. An electric traction drive of the work machine is controlled 601 by a closed-loop controller using the control signal as an input (e.g., to set an operating point of the traction drive). A mode of the work machine being changed by the operator is determined 602, e.g., based on a user interface input. A coefficient of the closed loop controller is adjusted 603 in response to the changed mode.

[0051] In FIG. 7, a flowchart shows a method of compensating for drift of an input sensor according to another example embodiment. The method involves detecting 700 activation and deactivation of a lockout control that activates or deactivates motion of an electric traction drive of a work machine. Before the lockout control is set to activate the work machine, a zero-force value of an input sensor is measured 701. The force sensor detects force applied to or movement of a handle of the work machine by an operator. After the lockout control is set to activate the work machine, values of a control signal of the input sensor are adjusted 702 by the zero-force value. The adjusted values of the control signal are used 703 to affect a speed of the electric traction drive, e.g., control the speed in response to operator inputs at the handle.

[0052] In some embodiments above, a walk-behind work machine engages a crawl mode in which a controller allows an electric traction drive to move within a second speed range less than a first speed range, the first speed range being a full speed range, normal speed range, or the like. In some walk-behind machines with non-electric traction drivesPATENTDocket No. 0206.000346W001 (P01942-W001)(e.g., ICE traction drive), the speed of the traction unit is controlled via mechanical means. One example is described in U.S. Patent 6,082,083, dated July 4, 2000 (hereinafter the ‘“083 patent”), in which a sliding handle grip is coupled to a transmission rocking mechanism via a cable. The rocking / rotating of the transmission at different angles changes slip between a drive pulley and a belt, thereby affecting speed of the machine. In such an arrangement, a crawl mode could be implemented using mechanical speed limiting means.

[0053] In FIGS. 8 and 9, diagrams show a simplified view of a mechanically implemented crawl mode according to an example embodiment. A handle 800 is coupled to a machine frame, e.g., similar to handle 108 and frame 102 as shown in FIG. 1. A slidable grip 802 is slidable along the handle 800, which causes a control cable 804 to affect a rocking angle of a pulley-driven transmission. Further details of the operation of this type of mechanism can be found in the ‘083 patent, and other variable transmissions may be used that change in response to mechanical inputs from a control cable, lever, or the like, e.g., a hydraulically driven transmission.

[0054] In FIG. 8, the grip 802 is pulled away from the walk-behind machine, as indicated by arrow 806. The position shown in FIG. 8 represents a low and / or minimum traction speed, e.g., pulling on the grip 802 will slow down or stop the machine’s traction unit. In FIG. 9, the grip 802 is pulled backwards relative to the walk-behind machine is indicated by arrow 806. The position shown in FIG. 9 represents a high and / or maximum traction speed, e.g., pushing on the grip 802 will speed up the machine’s traction unit.

[0055] The handle 800 is shown with stops 806, 807 affixed to an outer surface, e.g., permanently affixed, threaded into place, etc. The grip 802 includes adjustable sliders 808, 809 that can be adjustably moved into a position as indicated by arrows 810, 811. The sliders 808, 809 may move within slots 812, 813 on the outer edge of the grip 802, and may be held in place via ratcheting features on an outer surface of the grip 802 that interface with corresponding features on the sliders 808, 809. The sliders 808, 809 may be biased (e.g., spring loaded) in such an embodiment so that they can be pulled out, moved, and are biased back into position after release. Other mechanisms known in the art can bePATENTDocket No. 0206.000346W001 (P01942-W001) used, such as threaded knobs that are screwed and unscrewed to attach and release the sliders 808, 809.[00561 InFIGS. 8 and 9, the sliders 808, 809 are located at a maximum speed range position such that they have no effect on the maximum or minimum speed of the traction unit. This corresponds to the normal mode of the work machine’s traction unit traction, with the range between maximum and minimum being a first speed range. In other words, the slider 808 is shown at its furthest adjustable position in the direction indicated by arrow 811, and slider 809 is shown at its furthest adjustable position in the direction indicated by arrow 810.

[0057] The sliders 808, 809 can be adjusted to contact the stops such that the grip 802 will allow the traction drive to only move within a second speed range less than the first speed range. For example, moving slider 809 in the direction indicated by arrow 811 will limit the distance the grip 802 moves in the direction of the arrow 900 in FIG. 9, thus limiting the maximum speed of the traction unit. Thus, this slider 809 may be referred to as a maximum speed limit slider. Similarly, moving slider 808 in the direction of the arrow 810 will limit the distance the grip 802 moves in the direction of the arrow 806 in FIG. 8, thus limiting the minimum speed of the traction unit. Thus, this slider 808 may be referred to as a minimum speed limit slider.

[0058] In some embodiments, only the stop 807 and maximum speed limit slider 809 may be used to limit a maximum traction unit speed without affecting a lower limit on speed as provided by stop 806 and slider 808. This can be used to implement a crawl mode as described above where a reduced speed range is enforced. In such a case, the grip 802 can be pulled in direction 806 the full distance (e.g., limited by contact between grip 802 and handle) in order to slow stop the traction unit as in existing configurations.

[0059] In order to implement a fixed speed crawl mode in which the handle assembly causes the traction drive to move at a fixed speed regardless of pushing or pulling forces on the handle, the stop 806 and minimum speed limit slider 808 may be used together with the stop 807 and maximum speed limit slider 809. In order to allow the operator to override the lower speed limit, a release mechanism, illustrated here as trigger 816 and mechanism 817 can be used to disengage the slider 808 and / or stop 806. Thus thePATENTDocket No. 0206.000346W001 (P01942-W001) operator can engage (e.g., squeeze) the trigger 816, pull on the grip 802 in direction 806 to slow or halt the traction unit. If the walk-behind machine has other mechanisms to stop the traction unit independent of the grip 802 (e.g., “dead man’s switch”), the trigger 816 and mechanism 817 may not be needed.

[0060] In FIG. 10, the maximum speed limit slider 809 is shown having been adjusted downwards as indicated by arrow 1000. The minimum speed limit slider 808 is not moved from a no-lower-limit position. Thus the location of the grip 802 relative to the handle 800 as shown in FIG. 10 represents an adjusted maximum speed position. The grip 802 can move between the adjusted maximum speed position and default minimum speed, resulting in a reduced speed range.

[0061] In FIG. 11, the maximum speed limit slider 809 is shown having been adjusted downwards as indicated by arrow 1100, and the minimum speed limit slider 808 is shown having been adjusted upwards as indicated by arrow 1101. Thus the location of the grip 802 relative to the handle 800 as shown in FIG. 10 represents a fixed speed position. Operator inputs to the grip 802 will not have an effect on speed, although the traction unit can still be slowed or stopped by activating the trigger 816 as previously described.

[0062] Another mode previously described as being implemented in an electric traction drive is a brake control mode in which the controller moves the electric traction drive in a predetermined forward speed independent of the forward force applied to the input sensor and slows the electric traction drive from the predetermined forward speed proportional to a reverse force applied to the input sensor. This can also be implemented using mechanical means, as shown by example in FIG. 12. The handle 800, grip 802, maximum limit slider 809 and pin 807 are shown similar to like-named components previous examples. Also shown is a biasing member 1200, which may be implemented as a tensioning spring between the grip 802 and the handle 800.

[0063] The maximum speed limit slider 809 is shown being moved by distance 1202, thereby limiting a maximum speed of the traction unit to an adjusted maximum speed as previously described. The force applied by the biasing member 1200 is sufficient to return the grip 802 to the adjusted maximum speed position when the operator does notPATENTDocket No. 0206.000346W001 (P01942-W001) pull on the grip 802, although the operator may maintain contact on the grip 802 with a mild force. If the operator’s pulling force (which is in direction 806) is sufficient, then the grip 802 will overcome the biasing member force and move in direction 806, thereby slowing the traction unit. If the operator then releases the grip 802, the biasing member 1200 will return the grip 802 to the adjusted maximum speed position.

[0064] It will be understood that the particular mechanical embodiments described in FIGS. 8-12 are merely exemplary, and many equivalents can be implemented. Mechanical components known in the art such as brakes, pins and holes, stop screws, and the like can provide adjustable stops between two moving parts. Generally, an adjustable maximum speed limiting means may include a mechanism or means to mechanically limit the travel of the grip 802 in the pushing direction 900 relative to the handle 800. The distance that the travel is limited can be selected by the operator manually, preferably without the use of tools.

[0065] Similarly, an adjustable minimum speed limiting means may include a mechanism to mechanically limit the travel of the grip 802 in the pulling direction 806 relative to the handle, and the distance of the travel can be adjusted by the operator manually, preferably without the use of tools. A braking mode may be implemented using an adjustable maximum speed limiting means as described above together with a selectable biasing means to return the grip 802 and handle 800 to the adjusted maximum speed position in the absence of a pulling force by the operator and regardless of an amount of pushing force on the grip. Preferably, the selectable biasing means can be engaged and disengaged by the operator without the use of tools.

[0066] While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the specific illustrative aspects provided below. Various modifications of the illustrative aspects, as well as additional aspects of the disclosure, will become apparent herein.

[0067] Example l is a walk-behind work machine, comprising: an electric traction drive operable to move the work machine and an input sensor that detects force applied to or movement of a handle of the work machine by an operator and provides a control signal in response thereto. The control signal is used to affect a speed of the electric tractionPATENTDocket No. 0206.000346W001 (P01942-W001) drive. The work machine includes a lockout control that activates or deactivates motion of the work machine a controller operable to provide control of the electric traction drive. The controller is further operable to: measure a zero-force value of the control signal before the lockout control is set to activate the traction control; and adjust subsequent values of the control signal by the zero-force value when the traction control is activated and the operator is applying force to the input sensor to move the work machine.

[0068] Example 2 includes the work machine of example 1, wherein the controller provides open-loop control of the electric traction control. Example 3 includes the work machine of example 1, wherein the controller provides closed-loop control of the electric traction control, and wherein a movement sensor or a motor current sensor provides a feedback signal for the closed-loop control.

[0069] Example 4 includes the work machine of any one of examples 1-3, wherein detecting the zero-force value of the control signal comprises calculating a time-averaged value of the control signal before the lockout control is set to activate the traction control. Example 5 includes the work machine of any one of examples 1-4, wherein adjusting the subsequent values of the control signal by the zero-force value compensates for a drift in the input sensor when no force is applied to the input sensor. Example 6 includes the work machine of any one of examples 1-5, wherein the input sensor comprises a piezo sensor or a strain sensor.

[0070] Example 7 includes the work machine of any one of examples 1-6, wherein the lockout control activates or deactivates the motion of the work machine multiple times during a work session, and wherein different measurements of the zero-force value is made each of the multiple times, each of the different measurements being used adjust the subsequent control signal after each of the multiple activations. Example 8 includes the work machine any one of examples 1-7, wherein the lockout control activates or deactivates motion of the work machine in response to a presence or non-presence of an operator.

[0071] Example 9 is method, comprising: detecting activation and deactivation of a lockout control that activates or deactivates motion of an electric traction drive of a work machine; before the lockout control is set to activate the work machine, measuring a zero-PATENTDocket No. 0206.000346W001 (P01942-W001) force value of an input sensor that detects force applied to or movement of a handle of the work machine by an operator; after the lockout control is set to activate the work machine, adjusting values of a control signal of the input sensor by the zero-force value; and using the adjusted values of the control signal to affect a speed of the electric traction drive.

[0072] Example 10 is a walk-behind work machine, comprising: an electric traction drive operable to move the work machine and an input sensor that detects force applied to or movement of a handle of the work machine by an operator and provides a control signal in response thereto. The control signal is used to affect a speed of the electric traction drive. The work machine includes a mode control device that accepts operator input to change a mode of the work machine and a controller operable to provide control of the electric traction drive. The controller is further operable to: determine the mode of the work machine being changed via the mode control device; and adjust a coefficient of the controller in response to the change in the mode.

[0073] Example 11 includes the work machine of example 10, wherein the change of mode comprises changing an operational state of a work implement of the work machine. Example 12 includes the work machine of example 11, wherein the change of the operational state comprises a change in height of cut of the work implement. Example 13 includes the work machine of example 11 or 12, wherein the change of the operational state comprises a change in transport speed of the work machine. Example 14 includes the work machine of any one of examples 11-13, wherein the change of the operational state comprises an activation or deactivation of the work implement. Example 15 includes the work machine of any one of examples 11-14, wherein the change of the operational state comprises a change in speed of the work implement. Example 16 includes the work machine of any one of examples 11-16, wherein the change of the operational state comprises a change in direction of rotation of the work implement.

[0074] Example 17 includes the work machine of any one of examples 10-16, wherein the change of mode comprises changing between: a normal mode in which the closed-loop controller allows the electric traction drive to move within a first speed range; and a crawl mode in which the closed-loop controller allows the electric traction drive to move within a second speed range less than the first speed range. Example 18 includes thePATENTDocket No. 0206.000346W001 (P01942-W001) work machine of any one of examples 10-17, wherein the change of mode comprises changing between: a normal mode in which the closed-loop controller allows the electric traction drive to move within a first speed range; and a crawl speed mode in which the closed-loop controller causes the electric traction drive to move at a fixed speed regardless of the control signal. Example 19 includes the work machine of example 18, wherein the fixed speed is at a low end of the first speed range.

[0075] Example 20 includes the work machine any one of examples 9-19, wherein the change of mode comprises changing between: a normal mode in which the closed-loop controller moves the electric traction drive in a forward speed proportional to a forward force applied to the input sensor; and a brake control mode in which the closed-loop controller moves the electric traction drive in a predetermined forward speed independent of the forward force applied to the input sensor and slows the electric traction drive from the predetermined forward speed proportional to a reverse force applied to the input sensor.

[0076] Example 21 includes the work machine of example 20, wherein a relationship between the forward force and the forward speed is non-linear. Example 22 includes the work machine of example 20, wherein a relationship between the reverse force and slowing of the predetermined forward speed is non-linear. Example 23 includes the work machine of any one of claims 20-22, wherein the controller comprises a closed-loop controller.

[0077] Example 24 is method comprising: detecting a control signal in response to forces applied to a handle of a work machine by an operator; controlling an electric traction drive of the work machine by a controller using the control signal as an input; determining a mode of the work machine being changed by the operator; and adjusting a coefficient of the controller in response to the change in the mode. Example 19 includes the work machine of example 18, wherein the fixed speed is at a low end of the first speed range.

[0078] Example 25 is walk-behind work machine, comprising: a traction drive operable to move the work machine, a traction speed of the traction drive being variable in response to a mechanical input to the traction drive; a handle extending from the work machine to allow an operator to guide the work machine during its movement; a handlePATENTDocket No. 0206.000346W001 (P01942-W001) grip that slides on the handle in response to operator-applied forces in respective pulling and pushing directions, the sliding of the handle grip changing the mechanical input and thereby respectively decreasing and increasing the ground speed of the walk behind work machine; and an adjustable maximum speed limiting means that selectably limits the relative movement of the grip in the pushing direction relative to the handle.

[0079] Example 26 includes the work machine of example 25, wherein the adjustable maximum speed limiting means facilitates operator selection between a normal mode in which the traction drive is allowed to move within a first speed range and a crawl mode in which traction drive is allowed to move within a second speed range less than the first speed range. Example 27 includes the work machine of example 26, further comprising a selectable biasing means to return the grip and handle to an adjusted maximum speed position in the absence of a pulling force by the operator. Example 28 includes the work machine of example 27, wherein the adjustable maximum speed limiting means and the selectable biasing means facilitate a brake control mode in which the traction drive moves at an adjusted maximum speed regardless of an amount of pushing force on the grip, and wherein the traction unit slows in response to a pulling force applied to the grip. Example 29 includes the work machine of example 26, further comprising an adjustable minimum speed limiting means that selectably limits the relative movement of the grip in the pulling direction relative to the handle. Example 30 includes the work machine of example 29, wherein the adjustable maximum speed limiting means and the adjustable minimum speed limiting means facilitates a crawl speed mode in which the traction drive moves at a fixed speed regardless of a pulling force or a pushing force applied to the grip.

[0080] It is noted that the terms “have,” “include,” “comprises,” and variations thereof, do not have a limiting meaning, and are used in their open-ended sense to generally mean “including, but not limited to,” where the terms appear in the accompanying description and claims. Further, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably herein. Moreover, relative terms such as ’’left,” “right,” “front,” “fore,” “forward,” “rear,” “aft,” “rearward,” “top,” “bottom,” “side,” “upper,” “lower,” “above,” “below,” “horizontal,” “vertical,” and the like may be used herein and, ifPATENTDocket No. 0206.000346W001 (P01942-W001) so, are from the perspective shown in the particular figure, or while the machine is in an operating configuration. These terms are used only to simplify the description, however, and not to limit the interpretation of any embodiment described. As used herein, the terms “determine” and “estimate" may be used interchangeably depending on the particular context of their use, for example, to determine or estimate a position or pose of a vehicle, boundary, obstacle, etc.

[0081] Further, it is understood that the description of any particular element as being connected to or coupled to another element can be directly connected or coupled, or indirectly coupled / connected via intervening elements.

[0082] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about,” e.g., within ±10%. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

[0083] The various embodiments described above may be implemented using circuitry, firmware, and / or software modules that interact to provide particular results. One of skill in the arts can readily implement such described functionality, either at a modular level or as a whole, using knowledge generally known in the art. For example, the flowcharts and control diagrams illustrated herein may be used to create computer-readable instructions / code for execution by a processor. Such instructions may be stored on a non- transitory computer-readable medium and transferred to the processor for execution as is known in the art. The structures and procedures shown above are only a representative example of embodiments that can be used to provide the functions described hereinabove.

[0084] Note that any components described herein using terms such as “processor,” “controller,” “logic circuit,” “CPU,” or the like may be implemented using a plurality of discrete units operating together. For example, a processer that performs a series of steps or operations may be construed as two or more processors operating cooperatively toPATENTDocket No. 0206.000346W001 (P01942-W001) perform the steps. Similarly, other processing hardware such as memory and input-output may perform the described functions with multiple discrete units operating cooperatively or being coordinated by another unit, e.g., by a central processor or processors.

[0085] The foregoing description of the example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. Any or all features of the disclosed embodiments can be applied individually or in any combination and are not meant to be limiting, but purely illustrative. It is intended that the scope of the invention be limited not with this detailed description, but rather determined by the claims appended hereto.

Claims

PATENTDocket No. 0206.000346W001 (P01942-W001)CLAIMS:

1. A walk-behind work machine, comprising: an electric traction drive operable to move the work machine; an input sensor that detects force applied to or movement of a handle of the work machine by an operator and provides a control signal in response thereto, the control signal used to affect a speed of the electric traction drive; a lockout control that activates or deactivates motion of the work machine; and a controller operable to provide control of the electric traction drive, the controller further operable to: measure a zero-force value of the control signal before the lockout control is set to activate the traction control; and adjust subsequent values of the control signal by the zero-force value when the traction control is activated and the operator is applying force to the input sensor to move the work machine.

2. The work machine of claim 1, wherein the controller provides open-loop control of the electric traction control.

3. The work machine of claim 1, wherein the controller provides closed-loop control of the electric traction control, and wherein a movement sensor or a motor current sensor provides a feedback signal for the closed-loop control.

4. The work machine of claim 3, further comprising a mode control device that accepts operator input to change a mode of the work machine, and wherein the controller is further operable to: determine the mode of the work machine being changed via the mode control device; and adjust a coefficient of the closed-loop controller in response to the change in the mode.PATENTDocket No. 0206.000346W001 (P01942-W001)5. The work machine of any previous claim, wherein measuring the zero-force value of the control signal comprises calculating a time-averaged value of the control signal before the lockout control is set to activate the traction control.

6. The work machine of any previous claim, wherein adjusting the subsequent values of the control signal by the zero-force value compensates for a drift in the input sensor when no force is applied to the input sensor.

7. The work machine of any previous claim, wherein the input sensor comprises at least one of a piezo sensor, a strain sensor, a resistive sensor, or a pressure sensor.

8. The work machine of any previous claim, wherein the lockout control activates or deactivates the motion of the work machine multiple times during a work session, and wherein different measurements of the zero-force value is made each of the multiple times, each of the different measurements being used adjust the subsequent control signal after each of the multiple activations.

9. The work machine of any previous claim, wherein the lockout control activates or deactivates motion of the work machine in response to a presence or non-presence of an operator.

10. A method, comprising: detecting activation and deactivation of a lockout control that activates or deactivates motion of an electric traction drive of a work machine; before the lockout control is set to activate the work machine, measuring a zeroforce value of an input sensor that detects force applied to or movement of a handle of the work machine by an operator; after the lockout control is set to activate the work machine, adjusting values of a control signal of the input sensor by the zero-force value; andPATENTDocket No. 0206.000346W001 (P01942-W001) using the adjusted values of the control signal to affect a speed of the electric traction drive.

11. The method of claim 10, wherein measuring the zero-force value of the control signal comprises calculating a time-averaged value of the control signal before the lockout control is set to activate the traction control.

12. The method of any previous method claim, wherein adjusting the subsequent values of the control signal by the zero-force value compensates for a drift in the input sensor when no force is applied to the input sensor.

13. The method of any previous method claim, wherein the lockout control activates or deactivates the motion of the work machine multiple times during a work session, and wherein different measurements of the zero-force value is made each of the multiple times, each of the different measurements being used adjust the subsequent control signal after each of the multiple activations.

14. The method of any previous method claim, wherein the controller provides closed- loop control of the electric traction control, and wherein a movement sensor or a motor current sensor provides a feedback signal for the closed-loop control, the method further comprising: determining a mode of the work machine being changed via a mode control device; and adjusting a coefficient of the closed-loop controller in response to the change in the mode.

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