Method for evaluating friction between a floor and a trolley wheel

Abstract

Method for evaluating friction between a ground (10) and a trolley wheel (20) by means of a test device (30) comprising a chassis (31) and an upright (32), the wheel (20) being fixedly mounted on the chassis (31) and in contact with the ground (10) at a contact point (C), the method comprising: applying a test force (ER) to the upright (32) of the test device (30) at a support height (HA); estimating an actual friction coefficient between the wheel (20) and the ground (10) relative to a threshold friction coefficient (µs). Abstract figure: Figure 1

Description

Title of the invention: Method for evaluating friction between a ground and a trolley wheel Technical field

[0001] The present description relates to a method for evaluating friction between a ground and a trolley wheel. The present description also relates to an assembly comprising a trolley wheel and a test device for implementing said method for evaluating friction between a ground and the wheel. Prior art

[0002] Traditionally, in the field of logistics and more particularly in the preparation of an order in a warehouse, a human operator moves around the warehouse to collect one or more items from the order in different shelves of the warehouse. The operator may have to travel long distances which causes fatigue. Also, the operator must be perfectly familiar with the layout of the shelves in the warehouse at the risk of traveling a route which is not optimized and therefore longer, which increases the preparation time of the order.

[0003] In order to limit operator fatigue and reduce order preparation time, it is known to use a fleet of motorized, automatically guided trolleys. Such an environment is known as an automated storage and retrieval system (ASRS). Such a trolley typically comprises a chassis configured to receive one or more items and a plurality of motorized wheels allowing the trolley to move around the warehouse. As mentioned above, each trolley is automatically guided so as to travel around the warehouse along an optimized path in order to collect the items in the order.To determine the position of each trolley in the warehouse, the trolley comprises a plurality of sensors, in particular a trolley position sensor by remote sensing of markers in the warehouse (for example by means of a lidar whose acronym stands for "laser imaging detection and ranging" in English) and a revolution counter for each of the wheels.

[0004] When the trolley moves in the warehouse, one or more of the trolley wheels may possibly slide on the warehouse floor instead of rolling if the coefficient of friction between the wheel and the floor is not high enough, for example due to the floor covering, the quality of the slab, the wear of the floor or the degree of roughness of the floor. In the event of wheel slippage, the wheel revolution counter is not incremented due to the absence of rolling of the wheel while an actual movement of the trolley takes place. This results in a decorrelation between the measurement of the trolley position sensor and the measurement of the wheel revolution counter. In this event, for safety measures, the automatic control of the trolley can be configured to stop the trolley, thus stopping the preparation of the order and possibly blocking access to other trolleys.

[0005] In order to prevent this situation and limit the resulting costs, it is desirable to verify that the coefficient of friction between the wheels of the trolleys and the warehouse floor is greater than a minimum threshold value before installing an ASRS in the warehouse. However, current solutions for determining this coefficient of friction are complex, expensive and time-consuming, in particular due to the large number of sensors used to determine the coefficient of friction.

[0006] The present description aims in particular to provide a simple, economical and effective solution to the problems mentioned above. Summary

[0007] A method is proposed for evaluating friction between a ground and a trolley wheel relative to a threshold friction coefficient, the method being implemented by means of a test device comprising a chassis and an upright, said upright extending at least in a vertical direction and being integral with the chassis, the wheel being fixedly mounted on the chassis and in contact with the ground at a point of contact, the test device having a center of gravity offset from the point of contact, the method comprising: (a) the application of a test force horizontally to the upright of the test device at a support height determined as a function of the threshold friction coefficient, the test force having an intensity sufficient to produce a pivoting of the test device and the wheel at the point of contact or a movement of the wheel on the ground by sliding of the wheel on the ground, (b) in the case of pivoting of the test device and the wheel, the deduction that the actual coefficient of friction between the wheel and the ground is greater than or equal to the threshold coefficient of friction in order to assess the friction between the ground and the wheel.

[0008] In the event of slipping of the wheel on the ground, the method may comprise deducing that the actual coefficient of friction between the wheel and the ground is less than the threshold coefficient of friction in order to evaluate the friction between the ground and the wheel.

[0009] Said wheel may have an axis of rotation extending in a first horizontal direction. The center of gravity of said test device may be offset relative to the point of contact in a first direction of a second horizontal direction perpendicular to the first horizontal direction. The test force may be applied in a second direction of the second horizontal direction opposite to the first direction at a support height in the vertical direction relative to the point of contact, the test force having an intensity at least equal to a friction force between the wheel and the ground generated by a threshold friction coefficient so as to produce the pivoting of the test device and the wheel at the point of contact between the wheel and the ground around a pivot axis extending in the first horizontal direction or the displacement of the wheel and the test device in the second direction of the second direction by sliding of the wheel on the ground.

[0010] Said support height can be determined to be a minimum height in the vertical direction relative to the point of contact at which a theoretical force applied to the upright in the second direction of the second horizontal direction and with an intensity at least equal to a friction force between the wheel and the ground generated by the threshold friction coefficient, would cause the test device and the wheel to pivot at the point of contact between the wheel and the ground around a pivot axis extending in the first horizontal direction.

[0011] The floor may be that of a warehouse which includes an automated storage and retrieval system, said system comprising one or more trolleys, each trolley comprising one or more wheels, wherein a coefficient of friction between each wheel of each trolley is substantially equal to the actual coefficient of friction, plus or minus 10%.

[0012] The method may further comprise, following the analysis of the actual coefficient of friction between the wheel and the ground at the point of contact with respect to the threshold coefficient of friction: - moving the test device on the ground to place the wheel at another point of contact with the ground, - repetition of steps (a) and (b).

[0013] Said support height can be determined on the basis of a torque generated by the theoretical force applied at the support height having an intensity equal to a torque generated by the weight of the test device.

[0014] The test force can be applied to the amount in the form of a pulling force.

[0015] The test device may further comprise a second upright secured to the chassis and extending at least in the vertical direction, said second upright being offset relative to the point of contact in the first direction of the second horizontal direction and comprising a lower end by which it is rigidly connected to the chassis, a mass secured to said second upright being arranged vertically above the lower end of said second upright.

[0016] The wheel may be intended to receive a determined vertical load exerted by the weight of the trolley, the method comprising an adjustment of the mass to exert a vertical load substantially equal to the determined vertical load, or at least within 30% of the determined vertical load.

[0017] The chassis may comprise at least one side member which extends between a front end and a rear end in the first direction of the second horizontal direction, the wheel being locked in rotation on said at least one side member.

[0018] The chassis may comprise two side members extending in the second horizontal direction, the wheel being arranged between the two side members.

[0019] The chassis may comprise at least a first cross member extending in the first horizontal direction between the side members, the wheel being locked in rotation on the first cross member.

[0020] The amount of the test device can be rigidly connected to the first cross member.

[0021] The chassis may comprise a second cross member extending along the first horizontal direction between the two side members, the second cross member being offset from the point of contact between the wheel and the ground in the first direction of the second horizontal direction, the amount of the test device being rigidly connected to the second cross member.

[0022] According to another aspect, there is provided an assembly comprising a trolley wheel and a test device making it possible to implement the method for evaluating friction between a ground and a wheel as described above.

[0023] According to another aspect, a test device is described comprising a chassis and an upright. A wheel may be fixedly mounted on the chassis and in contact with the ground at a point of contact. Said wheel may have an axis of rotation extending in a first horizontal direction. The upright may be integral with the chassis and extend at least in a vertical direction. The test device may have a center of gravity offset from the point of contact in a first direction by a second horizontal direction perpendicular to the first horizontal direction.

[0024] The upright may be adapted to receive a force at a support height determined to be a minimum height in the vertical direction relative to the point of contact at which a theoretical force applied to the upright in the second direction of the second horizontal direction and with an intensity at least equal to a friction force between the wheel and the ground generated by the threshold friction coefficient, would cause the test device and the wheel to pivot at the point of contact between the wheel and the ground around a pivot axis extending in the first horizontal direction.

[0025] Said support height can be determined on the basis of a torque generated by the theoretical force applied at the support height having an intensity equal to a torque generated by the weight of the test device. In other words, the torque generated by the theoretical force applied at the support height opposes the torque generated by the weight of the test device.

[0026] The theoretical effort can be formulated by ET= ps.mg where - p, is the threshold friction coefficient between the wheel and the ground, - m is the mass of the test device, - g is the acceleration of gravity.

[0027] The torque generated by the theoretical force can be formulated by CT=ET.H where H is the support height in the vertical direction relative to the contact between the ground and the wheel, at which the theoretical force (ET) is applied to the upright.

[0028] The torque generated by the weight of the test device can be formulated by Cp=mgxg where - xg is the distance along the second horizontal direction which separates the contact between the wheel and the ground and the center of gravity of the chassis, - m is the mass of the test device, - g is the acceleration of gravity.

[0029] The support height can be determined by HA=xg / ps where - xg is the distance along the second horizontal direction which separates the contact between the wheel and the ground and the center of gravity of the chassis, - ps is the threshold friction coefficient between the wheel and the ground.

[0030] In other words, the upright may have a vertical dimension allowing the application of a force to the upright at the height. The upright may extend vertically between a lower end and an upper end. The vertical dimension of the upright may be considered between the lower end and the upper end. The lower end of the upright may be rigidly connected to the frame. The upper end of the upright may be free.

[0031] The amount may comprise one or more marks, each mark being associated with the value of a reference friction coefficient and arranged on the amount at a respective reference height at which a theoretical force applied to the amount of the test device in the second direction of the second horizontal direction and with an intensity at least equal to a friction force between the wheel and the ground generated by the reference friction coefficient would cause the test device and the wheel to pivot at the point of contact around the pivot axis.

[0032] A mark may be provided for each reference friction coefficient value between 0.2 and 0.8, preferably between 0.3 and 0.6, according to an increment of values ​​between 0.05 and 0.2, preferably equal to 0.1. In the case of a plurality of marks, the marks are distributed vertically along the upright.

[0033] According to a particular example, said one or more marks may comprise a mark associated with each of the following reference friction coefficient values: 0.3; 0.4; 0.5; 0.6.

[0034] For example, it may be provided: - a first mark associated with a first reference friction coefficient and arranged on the upright at a first reference height at which a theoretical force applied to the upright of the test device in the second direction of the second horizontal direction and having an intensity at least equal to the friction force between the wheel and the ground according to the first reference friction coefficient, would generate a pivoting of the test device and the wheel at the point of contact between the wheel and the ground around a pivot axis extending in the first horizontal direction; - a second mark associated with a second reference friction coefficient and arranged on the upright at a second reference height at which a theoretical force applied to the upright of the test device in the second direction of the second horizontal direction and having an intensity at least equal to the friction force between the wheel and the ground according to the second reference friction coefficient, would generate a pivoting of the test device and the wheel at the point of contact between the wheel and the ground around a pivot axis extending in the first horizontal direction; - a third mark associated with a third reference friction coefficient and arranged on the upright at a third reference height at which a theoretical force applied to the upright of the test device in the second direction of the second horizontal direction and having an intensity at least equal to the friction force between the wheel and the ground according to the third reference friction coefficient, would generate a pivoting of the test device and the wheel at the point of contact between the wheel and the ground around a pivot axis extending in the first horizontal direction; - a fourth mark associated with a fourth reference friction coefficient and arranged on the upright at a fourth reference height at which a theoretical force applied to the upright of the test device in the second direction of the second horizontal direction and having an intensity at least equal to the friction force between the wheel and the ground according to the fourth reference friction coefficient, would generate a pivoting of the test device and the wheel at the point of contact between the wheel and the ground around a pivot axis extending in the first horizontal direction.

[0035] The first, second, third and fourth reference friction coefficients may be equal to 0.3; 0.4; 0.5; 0.6 respectively.

[0036] Said one or more brands may comprise between 1 and 10 brands, preferably between 1 and 6 brands, more preferably between 1 and 4 brands.

[0037] The test device may comprise a second upright secured to the chassis and extending at least in a vertical direction, said second upright being offset relative to the point of contact in the first direction of the second direction ho and comprising a lower end by which it is rigidly connected to the chassis, a mass integral with said second upright being arranged vertically above the lower end of said second upright. The upright may comprise a free upper end. The mass may be arranged vertically between the upper end and the lower end of the upright. In a particular configuration, the upright on which the test force is applied merges with the second upright. Otherwise, according to an alternative, the device may comprise a single upright. Also, the mass may be integral with the single upright.

[0038] The mass may have a mass of between 10 kg and 30 kg, preferably of between 15 kg and 25 kg.

[0039] The chassis may comprise at least one side member which extends between a front end and a rear end in a first direction of the second horizontal direction, the wheel being locked in rotation on said at least one side member. The chassis may comprise two side members extending in the second horizontal direction, the wheel being arranged between the side members.

[0040] The chassis may comprise at least a first cross member extending in the first horizontal direction between the side members, the wheel being locked in rotation on the first cross member. The first cross member may extend along an axis coinciding with the axis of rotation of the wheel.

[0041] The upright of the test device may be rigidly connected to the first cross member. Alternatively, the chassis may comprise a second cross member extending in the first horizontal direction between the side members, the second cross member being offset from the point of contact between the wheel and the ground in the first direction of the second horizontal direction, the upright of the test device being rigidly connected to the second cross member. The second cross member may be offset from the first cross member in the first direction of the second horizontal direction. Alternatively again, the upright of the test device may be rigidly connected to the first cross member and the second upright may be rigidly connected to the second cross member.According to another alternative, the chassis comprises a third cross member extending in the first horizontal direction between the side members, the third cross member being offset from the point of contact between the wheel and the ground in the first direction of the second direction, the second upright of the test device being rigidly connected to the third cross member. The third cross member may be offset from the first cross member and / or the second cross member in the first direction of the second horizontal direction.

[0042] The wheel is placed closer to the front end than to the rear end of the test device.

[0043] Each side member may comprise a rear support member at the end rear. The rear support member of each side member may be resting on the ground when the wheel and the test device are in an initial configuration. In the initial configuration, the wheel and the test device may not be subjected to any external force, in particular other than gravity.

[0044] Each side member may comprise a front support member at the front end. The front support member of each side member may be supported on the ground when the wheel and the test device are in a tilted configuration. In the tilted configuration, the wheel and the test device may be pivoted about the pivot axis, in particular forward, preferably in response to the application of an external force.

[0045] The rear support member and / or the front support member may comprise a caster pivoting about a respective axis extending in the first horizontal direction. Brief description of the drawings

[0046] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0047] [Fig-1] is a schematic side view of a test device of the present invention. description.

[0048] [Fig.2] is a schematic perspective view of a test device of the present description, according to a first alternative.

[0049] [Fig.3] is a schematic side view of a test device of the present invention. description, according to a second alternative and according to a first mode of operation.

[0050] [Fig.4] is a schematic side view of a test device of the present invention. description, according to the second alternative and according to a second mode of operation.

[0051] [Fig.5] is a graph showing the relationship between a support height on the test device of figures 1 to 4 and a coefficient of friction between a wheel secured to the test device and a ground.

[0052] [Fig.6] is a functional diagram of an evaluation method implemented by means of of the test device of figures 1 to 5. Description of the embodiments

[0053] A method for evaluating friction between a floor 10 and a trolley wheel 20 is now described with reference to FIGS. 1 to 6. The trolley may be motorized. In this sense, the trolley may comprise a motor configured to enable the trolley to move. The wheel 20 may be motorized. In this sense, the wheel 20 may be a drive wheel to which the motor power is delivered. The evaluation may relate to a threshold friction coefficient ps- The evaluation may comprise comparing the actual friction coefficient pR between the floor 10 and the wheel 20 with the threshold friction coefficient ps- This evaluation may comprise determining that the co effective friction coefficient pR between the ground 10 and the wheel 20 is greater than, equal to or less than the threshold friction coefficient ps- The evaluation may include the approximate estimation of the effective friction coefficient pR between the ground 10 and the wheel 20.

[0054] The method is implemented by means of a test device 30 visible in Figures 1 to 4 according to several alternatives described below. Unless otherwise stated, the characteristics described below with respect to the test device 30 may be common to each of the alternatives. The test device 30 comprises a chassis 31 and an upright 32 secured to the chassis. The wheel 20 is fixedly mounted on the chassis 31 and in contact with the ground 10 at a contact point C. Said wheel 20 has an axis of rotation R. The axis of rotation R of said wheel 20 extends in a first horizontal direction XL. The upright 32 extends at least in a vertical direction Z. In the examples shown, the upright 32 extends in the vertical direction Z.The test device 30 also has a center of gravity offset relative to the contact point C in a first direction SI by a second horizontal direction X2 perpendicular to the first horizontal direction XL.

[0055] The method may comprise several steps shown schematically in the functional diagram of [Fig.6].

[0056] The method may comprise a first step 110. The first step 110 comprises the application of a test force ER on the upright 32 of the test device 30 at a support height HA in the vertical direction Z relative to the contact point C. The test force ER is applied in a second direction S2 of the second horizontal direction X2 opposite to the first direction SL. The test force ER may be applied above the contact point C or at a distance therefrom in the second horizontal direction X2, in the first direction SI or the second direction S2. The test force ER is applied with an intensity at least equal to a friction force between the wheel 20 and the ground 10 generated by a threshold friction coefficient ps. The application of the test force ER produces a pivoting Fl of the test device 30 and the wheel 20 at the contact point C or a displacement F2 of the wheel 20 on the ground 10 by sliding of the wheel 20 on the ground 10.

[0057] Said support height HA is determined to be a minimum height in the vertical direction Z relative to the contact point C at which a theoretical force ET applied to the upright 32 in the second direction S2 of the second horizontal direction X2 and with an intensity at least equal to a friction force between the wheel 20 and the ground 10 generated by the threshold friction coefficient ps, would cause the test device 30 and the wheel 20 to pivot at the contact point C between the wheel 20 and the ground 10 about a pivot axis P extending in the first horizontal direction XL. The determination of the support height HA can be carried out during a step preliminary to the first step 110 of the method. The determination of the support height can be carried out during a subsidiary step of the first step 110 of the method.

[0058] The method comprises a second step 120. The second step 120 can be carried out after the application of said test force ER. The second step 120 comprises the deduction that an actual friction coefficient pR between the wheel 20 and the ground 10 is greater than or equal to the threshold friction coefficient p, in the event of a pivoting F1 of the test device 30 and the wheel 20 at the contact point C around a pivoting axis P extending in the first horizontal direction X1 as shown in [Fig.3]. The pivoting axis P passes through or is close to the contact point C.

[0059] Such a method makes it possible to determine quickly and economically whether the actual coefficient of friction pR between the wheel 20 and the floor 10 is greater than or equal to the threshold coefficient of friction p„, the latter being advantageously chosen to guarantee that a trolley moving in the warehouse will not be subject to slippage of at least one of its wheels 20, in particular during acceleration or deceleration phases. The method is advantageous in that it makes it possible to decide according to a “Go / No Go” (or “Pass / Fail”) process as to the actual coefficient of friction pR between the wheel 20 and the floor 10 of the warehouse, without having to measure it digitally. Moreover, advantageously, the method does not use any sensor.

[0060] The floor may be that of a warehouse which includes an automated storage and retrieval system (or “ASRS”). The automated storage and retrieval system may include one or more trolleys, each trolley including one or more wheels 20. Each wheel 20 may be motorized. A coefficient of friction between each wheel 20 of each trolley may be substantially equal to the actual coefficient of friction pR, plus or minus 10%. The method may thus make it possible to verify the conformity of the coefficient of friction between the wheels of each trolley among a fleet of trolleys and the floor of the warehouse upstream of the installation of the ASRS.

[0061] Alternatively, the second step may comprise the deduction that the actual friction coefficient pR between the wheel 20 and the ground 10 is lower than the threshold friction coefficient p, in the event of a displacement F2 of the wheel 20 and the test device 30 in the second direction S2 of the second direction by sliding of the wheel 20 on the ground as shown in [Fig.4], following the application of the test force ER on the upright 32 of the test device 30 at the level of the support height HA in the second direction S2 of the second horizontal direction X2 and having an intensity at least equal to the friction force between the wheel 20 and the ground 10 according to the threshold friction coefficient pj.

[0062] Following the analysis of the actual friction coefficient pR between the wheel 20 and the ground 10 at the contact point C with respect to the threshold friction coefficient ps, the method can further understand: - moving the test device 30 on the ground 10 to place the wheel 20 at another point of contact Cl with the ground 10, - repeating steps 110 and 120.

[0063] According to the alternative of the second step, i.e. when there is sliding of the wheel 20 on the ground, the method may comprise a third step 130. The third step 130 may further comprise, following the deduction that the actual friction coefficient pR between the wheel 20 and the ground 10 is lower than the threshold friction coefficient p„, the modification of a surface condition of the wheel and / or of the warehouse floor. The modification of the surface condition of the wheel may comprise the modification of a material from which the peripheral external surface of the wheel is made; the modification of the surface condition of the warehouse floor may comprise the modification of a material from which an upper surface of the warehouse floor is made; and / or the addition of a surface coating on an upper surface of the floor.

[0064] Subsequently, the method may comprise the renewal of steps 110 and 120, that is to say the application of a test force ER on the upright 32 of the test device 30 at the level of the support height HA in the second direction S2 of the second horizontal direction X2 and according to an intensity at least equal to the friction force between the wheel 20 and the ground 10 generated by the threshold friction coefficient ps; and preferably the comparison of the actual friction coefficient pR between the wheel 20 and the ground 10 at the level of another contact point Cl with respect to the threshold friction coefficient ps, namely: - the deduction that an actual coefficient of friction pR between the wheel 20 and the ground 10 is greater than or equal to the threshold coefficient of friction p, in the case of pivoting Fl of the test device 30 and the wheel 20 at the point of contact C between the wheel 20 and the ground 10 around the pivot axis P; or - the deduction that the actual coefficient of friction between the wheel 20 and the ground 10 is lower than the threshold coefficient of friction p, in the event of displacement F2 of the wheel 20 and the test device 30 in the second direction S2 of the second direction by sliding of the wheel 20 on the ground.

[0065] Said support height HA can be determined on the basis of a torque generated by the theoretical force ET applied at the level of the support height HA having an intensity equal to a torque generated by the weight of the test device 30. In other words, the torque generated by the theoretical force ET applied at the level of the support height HA opposes the torque generated by the weight of the test device 30.

[0066] The theoretical effort ET can be formulated by ET=ps.mg where - is the threshold friction coefficient between wheel 20 and the ground, - m is the mass of the test device 30, - g is the acceleration of gravity.

[0067] The torque generated by the theoretical force ET can be formulated by CT=ET.H where H is the support height HA in the vertical direction Z relative to the contact C between the ground 10 and the wheel 20, at which the theoretical force ET on the upright 32.

[0068] The torque generated by the weight of the test device 30 can be formulated by Cp=mgxg where - xg is the distance along the second horizontal direction X2 which separates the contact C between the wheel 20 and the ground 10, and the center of gravity of the chassis 31, - m is the mass of the test device 30, - g is the acceleration of gravity.

[0069] The support height HA can be determined by HA=x„ / p, where - xg is the distance along the second horizontal direction X2 which separates the point of contact C between the wheel 20 and the ground 10, and the center of gravity of the chassis 31, - ps is the threshold friction coefficient between wheel 20 and the ground.

[0070] Also, as shown in [Fig. 5], there may be an inverse relationship between a reference height HR on the upright from the contact point C and a coefficient of friction pR according to which a theoretical force ET applied to the upright 32 in the second direction S2 of the second horizontal direction X2 and having an intensity at least equal to a friction force between the wheel 20 and the ground 10 according to the reference coefficient of friction pR, would generate a pivoting of the test device 30 and the wheel 20 at the contact C between the wheel 20 and the ground 10 around the pivot axis P. Advantageously, the determination of the support height may be independent of the test force applied to the upright.

[0071] Thus, in the event of pivoting F1 of the test device 30 and the wheel 20 at the contact C between the wheel 20 and the ground 10 around the pivot axis P, it can be deduced that the support height HA is greater than or equal to a reference height HR on the upright 32 at which a theoretical force ET applied to the upright 32 in the second direction S2 of the second horizontal direction X2 and having an intensity at least equal to a friction force between the wheel 20 and the ground 10 according to the threshold friction coefficient p„ would generate a pivoting of the test device 30 and the wheel 20 at the contact C between the wheel 20 and the ground 10 around the pivot axis P extending in the first horizontal direction XL. Consequently, due to the inverse relationship between the friction coefficient and the support height HA, it can be deduced that the actual friction coefficient pR is greater or equal to the threshold friction coefficient pj.

[0072] Conversely, in the event of the wheel 20 sliding on the ground 10, it can be deduced that the support height HA is lower than said reference height HR. Similarly, due to the inverse relationship between the coefficient of friction and the height support Ha, it can be deduced that the actual friction coefficient pR is lower than the threshold friction coefficient p,.

[0073] As shown in Figures 1 and 2, the upright 32 may comprise one or more marks 33, each mark 33 being associated with the value of a reference friction coefficient pR and arranged on the upright 32 at a respective reference height HR at which a theoretical force ET applied to the upright 32 of the test device 30 in the second direction S2 of the first horizontal direction XI and with an intensity at least equal to a friction force between the wheel 20 and the ground 10 generated by the reference friction coefficient pR, would cause the test device 30 and the wheel 20 to pivot at the contact point C around the pivot axis P.

[0074] The reference friction coefficient pR associated with one of the one or more marks 33 may correspond to the threshold friction coefficient ps- The support height Ha may be determined by identifying a mark 33 among said one or more marks 33 whose associated reference friction coefficient pR corresponds to the threshold friction coefficient ps- The test device 30 may comprise a handle or a strap secured to the upright 32 at each mark 33 to facilitate the application of the test force ER on the upright 32.

[0075] Alternatively, the support height can be determined by selecting the mark 33 having the minimum reference height HR. In the event of non-pivoting of the test device 30 and the wheel 20 at the contact point C about the pivot axis P after application of the test force ER, the steps 110 and 120 can be repeated with the support height determined by selecting the mark 33 positioned directly above the mark 33 having the minimum reference height HR. As long as the test device 30 and the wheel 20 do not pivot at the contact point C about the pivot axis P after application of the test force ER, the steps 110 and 120 can be repeated with the support height determined by selecting the mark 33 positioned directly above the previously sectioned mark 33. This ensures a quick and easy determination of the support height Ha as a function of the chosen threshold friction coefficient ps.In other words, the support height HA corresponds to the reference height HR of the mark 33 whose reference friction coefficient pR corresponds to the threshold friction coefficient p,. .

[0076] A mark 33 may be provided for each reference friction coefficient value pR between 0.2 and 0.8, preferably between 0.3 and 0.6, according to an increment of values ​​between 0.05 and 0.2, preferably equal to 0.1. In the case of a plurality of marks 33, the marks 33 are distributed vertically along the upright 32.

[0077] According to a particular example, said one or more marks 33 may include a mark 33 associated with each of the following values ​​of reference friction coefficient pR: 0.3; 0.4; 0.5; 0.6.

[0078] For example, it may be provided: - A first mark 331 associated with a first reference friction coefficient pRi and arranged on the upright 32 at a first reference height HRi at which a theoretical force En applied to the upright 32 of the test device 30 in the second direction S2 of the second horizontal direction X2 and having an intensity at least equal to the friction force between the wheel 20 and the ground 10 according to the first reference friction coefficient pRb would generate a pivoting of the test device 30 and the wheel 20 at the point of contact C between the wheel 20 and the ground 10 around a pivot axis P extending in the first horizontal direction XI; - A second mark 332 associated with a second reference friction coefficient pR2 and arranged on the upright 32 at a second reference height HR2 at which a theoretical force ET2 applied to the upright 32 of the test device 30 in the second direction S2 of the second horizontal direction X2 and having an intensity at least equal to the friction force between the wheel 20 and the ground 10 according to the second reference friction coefficient pR2, would generate a pivoting of the test device 30 and the wheel 20 at the point of contact C between the wheel 20 and the ground 10 around a pivot axis P extending in the first horizontal direction XI; - A third mark 333 associated with a third reference friction coefficient pR3 and arranged on the upright 32 at a third reference height HR3 at which a theoretical force ET3 applied to the upright 32 of the test device 30 in the second direction S2 of the second horizontal direction X2 and having an intensity at least equal to the friction force between the wheel 20 and the ground 10 according to the third reference friction coefficient pR3, would generate a pivoting of the test device 30 and the wheel 20 at the contact point C between the wheel 20 and the ground 10 around a pivot axis P extending in the first horizontal direction XI; - A fourth mark 334 associated with a fourth reference friction coefficient pR4 and arranged on the upright 32 at a fourth reference height HR4 at which a theoretical force ET4 applied to the upright 32 of the test device 30 in the second direction S2 of the second horizontal direction X2 and having an intensity at least equal to the friction force between the wheel 20 and the ground 10 according to the fourth reference friction coefficient pR4, would generate a pivoting of the test device 30 and the wheel 20 at the point of contact C between the wheel 20 and the ground 10 around a pivot axis P extending in the first horizontal direction XI.

[0079] The first, second, third and fourth reference friction coefficients p Ri ; pR2 ; pR3 ; pR4 may be equal to 0.3 ; 0.4 ; 0.5 ; 0.6 respectively. Said one or more marks 33 may comprise between 1 and 10 marks 33, preferably between 1 and 6 marks 33, more preferably between 1 and 4 marks 33.

[0080] Remarkably, the test force ER is applied to the upright 32 in the form of a pulling force. In the method as described, the coefficient of friction between the wheel 20 and the ground 10 may be a coefficient of static friction, i.e. linked to the force necessary to move the trolley on the ground. Also, the wheel 20 may be stationary when the step 110 is initiated. Alternatively, the test force ER may be applied to the upright 32 in the form of a pushing force in the second direction S2 of the second horizontal direction X2.

[0081] With reference to [Fig.l], the test device 30 may further comprise a second upright 32a secured to the chassis 31 and extending at least in a vertical direction Z. Said second upright 32a may be offset relative to the contact point C in the first direction S1 of the second horizontal direction X2 and comprise a lower end by which it is rigidly connected to the chassis 31. The test device 30 may comprise a mass 34 secured to said second upright 32a and arranged vertically above the lower end of said second upright 32a. The mass 34 makes it possible to increase the position yg of the center of gravity of the test device 30 in the vertical direction Z, which makes it possible to modify the stability of the test device 30, iethe unstable equilibrium point of the test device 30, during a pivoting of the test device 30 and the wheel 20 around the pivot axis P in order to deduce more easily and more quickly that the actual coefficient of friction pR between the wheel 20 and the ground 10 is greater than or equal to the threshold coefficient of friction p,. The upright 32 may comprise a free upper end. The mass may be arranged vertically between the upper end and the lower end of the upright 32. .

[0082] In a particular configuration shown in [Fig.2], the upright 32 on which the test force is applied merges with the second upright 32a. In other words, according to an alternative, the device may comprise a single upright 32. Also, the mass 34 may be integral with the single upright 32.

[0083] The wheel 20 is intended to receive a determined vertical load exerted by the weight of the trolley. For this purpose, the method may comprise an adjustment of the mass 34 to exert a vertical load substantially equal to the determined vertical load, or at least within 30% of the determined vertical load. The mass 34 may have a mass of between 10 kg and 30 kg, preferably of between 15 kg and 25 kg. The mass 34 is chosen so that the weight exerted on the wheel 20 of the test device corresponds to the weight exerted on a wheel 20 of the trolley.

[0084] The chassis 31 may comprise at least one side member which extends between a front end and a rear end in the first direction S1 of the second horizontal direction X2. The wheel 20 may be locked in rotation on said at least one side member. The chassis 31 may comprise two side members extending in the second horizontal direction X2. The wheel 20 may be arranged between the side members. The chassis 31 is thus more stable.

[0085] The chassis 31 may comprise at least a first cross member 37 extending in the first horizontal direction XI between the side members. The wheel 20 may be locked in rotation on the first cross member 37. The first cross member may extend along an axis coinciding with the axis of rotation R of the wheel 20. The upright 32 of the test device 30 may be rigidly connected to the first cross member 37 as shown in [Fig.l].

[0086] Alternatively, as seen in Figures 2, 4 and 5, the chassis 31 may comprise a second cross member 38 extending in the first horizontal direction XI between the side members. The second cross member 38 may be offset relative to the point of contact C between the wheel 20 and the ground 10 in the first direction of the second horizontal direction X2. The upright 32 of the test device 30 may be rigidly connected to the second cross member 38. This alternative makes it possible to promote the offset of the center of gravity offset relative to the point of contact C between the wheel 20 and the ground 10 in the first direction SI of the second horizontal direction X2 perpendicular to the first horizontal direction XL. The second cross member 38 may be offset relative to the first cross member 37 in the first direction of the second horizontal direction X2.

[0087] With reference to [Fig.l], the upright 32 of the test device 30 may be rigidly connected to the first crosspiece 37 and the second upright 32a may be rigidly connected to the second crosspiece 38.

[0088] According to an alternative not shown, the chassis 31 comprises a third cross member extending in the first horizontal direction XI between the side members, the third cross member being offset relative to the point of contact C between the wheel 20 and the ground 10 in the first direction of the second direction, the second upright 32a of the test device 30 being rigidly connected to the third cross member. The third cross member 38 may be offset relative to the first cross member 37 and / or the second cross member 38 in the first direction of the second horizontal direction X2. In this alternative, the wheel 20 being fixed to the first cross member 37, the upright 32 is rigidly connected, respectively, to the second cross member 38 or the third cross member, and the second upright 32a is rigidly connected to the third cross member or the second cross member 38.

[0089] Preferably, the wheel 20 is arranged closer to the front end than to the rear end of the test device. This ensures a center of gravity offset from the point of contact C between the wheel 20 and the ground 10 in the first direction SI of the second horizontal direction X2.

[0090] Each side member may comprise a rear support member 35 at the rear end, the rear support member 35 of each side member being supported on the ground 10 when the wheel 20 and the test device 30 are in an initial configuration. The wheel 20 and the test device 30 are in the initial configuration before the application of the test force ER on the test device 30. In this case, the initial configuration may be said to be “at rest” (for example, visible in [Fig. 1]).The wheel 20 and the test device 30 may be in the initial configuration when no pivoting of the test device 30 and the wheel 20 at the contact point C around the pivot axis P is generated by the test force ER applied to the upright 32 of the test device 30 at the support height HA in the second direction S2 of the second horizontal direction X2 and with an intensity at least equal to the friction force between the wheel 20 and the ground 10 generated by the threshold friction coefficient p„, that is to say when the application of the test force ER generates a displacement F2 of the wheel 20 and the test device 30 in the second direction S2 of the second direction by sliding of the wheel 20 on the ground (for example, visible in [Fig.5]).

[0091] Each side member may comprise a front support member 36 at the front end, the front support member 36 of each side member being supported on the ground 10 when the wheel 20 and the test device 30 are in a tilted configuration. The wheel 20 and the test device 30 are in the tilted configuration when the wheel 20 and the test device 30 have pivoted about the pivot axis P after application of the test force ER (for example, visible in [Fig. 4]).

[0092] The rear support member 35, respectively the front support member 36, may comprise a caster pivoting around a respective axis extending in the first horizontal direction XL

Claims

Claims

1. Method for evaluating friction between a ground (10) and a trolley wheel (20) relative to a threshold friction coefficient (ps), the method being implemented by means of a test device (30) comprising a chassis (31) and an upright (32), said upright (32) extending at least in a vertical direction (Z) and being integral with the chassis (31), the wheel (20) being fixedly mounted on the chassis (31) and in contact with the ground (10) at a contact point (C), the test device (30) having a center of gravity offset relative to the contact point (C), the method comprising: (a) applying a test force (ER) horizontally to the upright (32) of the test device (30) at a support height (HA) determined as a function of the threshold friction coefficient (ps),the test force (Er) having sufficient intensity to produce a pivoting (Fl) of the test device (30) and the wheel (20) at the contact point (C) or a displacement (F2) of the wheel (20) on the ground (10) by sliding of the wheel (20) on the ground (10), (b) in the case of a pivoting (Fl) of the test device (30) and the wheel (20), the deduction that the actual coefficient of friction (pR) between the wheel (20) and the ground (10) is greater than or equal to the threshold coefficient of friction (Ps) in order to evaluate the friction between the ground (10) and the wheel (20).,

2. A method according to claim 1 comprising, in the event of sliding of the wheel (20) on the ground (10), deducing that the actual coefficient of friction (pR) between the wheel (20) and the ground (10) is lower than the threshold coefficient of friction (ps) in order to evaluate the friction between the ground (10) and the wheel (20).

3. Method according to any one of the preceding claims, wherein, said wheel (20) having an axis of rotation (R) extending in a first horizontal direction (XI), the center of gravity of said test device (30) being offset relative to the point of contact (C) in a first direction (SI) of a second horizontal direction (X2) perpendicular to the first horizontal direction (XI), the test force (ER) is applied in a second direction (S2) of the second horizontal direction (X2) opposite to the first direction (SI) at a support height (Ha) in the vertical direction (Z) relative to the point of contact (C), the test force (ER) having an intensity at least equal to a friction force between the wheel (20) and the ground (10) generated by a co- efficient threshold friction (ps) so as to produce the pivoting of the test device (30) and the wheel (20) at the point of contact (C) between the wheel (20) and the ground (10) around a pivot axis (P) extending in the first horizontal direction (XI) or the displacement (F2) of the wheel (20) and the test device (30) in the second direction (S2) of the second direction by sliding of the wheel (20) on the ground (10).

4. Method according to claim 3, wherein said support height (HA) is determined to be a minimum height in the vertical direction (Z) relative to the contact point (C) at which a theoretical force (ET) applied to the upright (32) in the second direction (S2) of the second horizontal direction (X2) and with an intensity at least equal to a friction force between the wheel (20) and the ground (10) generated by the threshold friction coefficient (ps), would cause the test device (30) and the wheel (20) to pivot at the contact point (C) between the wheel (20) and the ground (10) around a pivot axis (P) extending in the first horizontal direction (XI).

5. A method according to any preceding claim, wherein the floor (10) is that of a warehouse which comprises an automated storage and retrieval system, said system comprising one or more trolleys, each trolley comprising one or more wheels (20), wherein a coefficient of friction between each wheel (20) of each trolley is substantially equal to the actual coefficient of friction, plus or minus 10%.

6. A method according to any preceding claim, the method further comprising, following analysis of the actual friction coefficient (pR) between the wheel (20) and the ground (10) at the contact point (C) relative to the threshold friction coefficient (ps): - moving the test device (30) over the ground (10) to place the wheel (20) at another contact point (Cl) with the ground (10), - repeating steps (a) and (b).

7. Method according to any one of the preceding claims, wherein said support height (HA) is determined on the basis of a torque generated by the theoretical force (ET) applied at the support height (Ha) having an intensity equal to a torque generated by the weight of the test device (30).

8. A method according to any preceding claim, wherein the test force (ER) is applied to the upright (32) in the form of a pulling effort.

9. Method according to any one of claims 3 to 8, wherein the test device (30) further comprises a second upright (32a) secured to the chassis (31) and extending at least in the vertical direction (Z), said second upright (32a) being offset relative to the contact point (C) in the first direction (SI) of the second horizontal direction (X2) and comprising a lower end by which it is rigidly connected to the chassis (31), a mass (34) secured to said second upright (32a) being arranged vertically above the lower end of said second upright (32a).

10. Method according to the preceding claim, in which the wheel (20) is intended to receive a determined vertical load exerted by the weight of the trolley, the method comprising an adjustment of the mass (34) to exert a vertical load substantially equal to the determined vertical load, or at least to within 30% of the determined vertical load.

11. Method according to any one of claims 3 to 10, in which the chassis (31) comprises at least one side member which extends between a front end and a rear end in the first direction (SI) of the second horizontal direction (X2), the wheel (20) being locked in rotation on said at least one side member.

12. Method according to the preceding claim, in which the chassis (31) comprises two side members extending in the second horizontal direction (X2), the wheel (20) being arranged between the two side members.

13. Method according to the preceding claim, in which the chassis (31) comprises at least a first cross member (37) extending in the first horizontal direction (XI) between the side members, the wheel (20) being locked in rotation on the first cross member (37).

14. Method according to the preceding claim, in which the upright (32) of the test device (30) is rigidly connected to the first crosspiece (37).

15. Method according to claim 13, in which the chassis (31) comprises a second cross member (38) extending in the first horizontal direction (XI) between the two side members, the second cross member (38) being offset relative to the point of contact (C) between the wheel (20) and the ground (10) in the first direction of the second horizontal direction (X2), the upright (32) of the test device (30) being rigidly connected to the second cross member (38).

16. Assembly comprising a wheel (20) for a trolley and a testing device (30) for implementing the method for evaluating friction between a ground (10) and a wheel (20) according to any one of the preceding claims.

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