Scissor lift configured to handle a blockage during platform descent and corresponding procedure

Abstract

The invention relates to a scissor lift comprising a platform, a hydraulic cylinder system (6) configured to actuate a platform lifting structure, a pressure sensor system (7) arranged to measure the pressure in the cylinder system, and a control unit (10) configured to prevent the platform from descending, at least when the lift is in a working position and when the measured pressure value (P7m) is below a minimum threshold value (P7s) defined for the height (H4) at which the platform is located, while the upward movement of the platform remains controllable. The invention also relates to a method for preventing descent and a corresponding method for enabling descent. Figure for the abstract: Fig. 2

Description

Title of the invention: Scissor lift configured to manage a blockage during platform descent and corresponding method FIELD OF THE INVENTION

[0001] The present invention relates generally to scissor lifts. PREVIOUS ART

[0002] Scissor lift type machines are used on construction and industrial sites.

[0003] A scissor lift usually comprises a rolling chassis, a work platform also called a basket, into which a user can climb, and a lifting structure which comprises one or more scissors to allow the platform to be raised or lowered to a given working height.

[0004] One of the main risks observed in the field is that the machine basket may hit an obstacle when the basket is lowered.

[0005] The operator may not realize that the machine basket is against the obstacle, such as a low wall. The machine may be damaged if the operator continues to control the basket's descent from the control panel and there is a safety risk for the operator in the basket.

[0006] The aim of the present invention is to propose a new machine and a new corresponding method making it possible to overcome all or part of the problems set out above. Summary of the invention

[0007] To this end, the invention relates to a person handling machine, called a nacelle, which comprises: - a rolling chassis equipped with a ground-moving drive motor system for the chassis; - a platform on which an operator is able to climb, and a control desk; - a lifting structure which extends between the chassis and the platform; the lifting structure comprising a scissor system capable of passing from a folded position in which the platform is in the lowered position to a deployed position in which the platform is in the raised position, and vice versa; - a height sensor system for measuring a parameter representative of the height of the platform; - a hydraulic cylinder system configured to control the folding and deployment of said scissor system; - a hydraulic circuit system comprising: - a hydraulic distributor, and - a hydraulic pump to bring pressurized oil into the hydraulic distributor, - a hydraulic supply line connected to the hydraulic distributor and the hydraulic cylinder system, and a solenoid valve configured to control the oil supply to the hydraulic cylinder system; - a pressure sensor system arranged to measure a pressure representative of the pressure in the hydraulic cylinder system; - a control unit configured to, from control instructions transmitted by the control panel, control the hydraulic circuit system to move the platform up or down: characterized in that the control unit is also configured to, at least when the nacelle is in a working position which is detected by the control unit when the height of the platform is greater than a given value: - compare the measured pressure value to a minimum threshold value which is defined according to the height at which the platform is located, and - when the measured pressure value is below the minimum threshold value defined for the height at which the platform is located, prevent the platform from descending, while the upward movement of the platform remains controllable.

[0008] Measuring the pressure in the hydraulic cylinder system makes it possible to detect, when the measured pressure is lower than a given threshold value, that the platform is at its bottom stop against an obstacle, such as a low wall, and to then trigger the stopping of the lowering movement and preferably to prevent the machine from moving on the ground, while authorizing the control of the raising of the platform to allow the nacelle to clear the obstacle.

[0009] Such a design makes it possible to reduce the risk of mechanical damage to the machine and the safety risk, in particular of falling, of the operator.

[0010] Otherwise, if the downward movement of the platform could be initiated while the platform was blocked on an obstacle, there would be a risk of significant or total loss of pressure in the cylinder system. The hydraulic cylinder system would then risk not being able to ensure retention of the platform during a potential release (voluntary or involuntary) of the platform from the obstacle.

[0011] The machine may also include one or more of the following characteristics taken in any technically admissible combination.

[0012] According to one embodiment, the solenoid valve is capable of having: - a non-return admission state in which the solenoid valve allows the supply of pressurized oil into the hydraulic cylinder system, the solenoid valve having a flap anti-return; - and an exhaust condition allowing the descent of oil from the hydraulic cylinder system to an oil reservoir of the hydraulic circuit system, to allow downward movement of the platform by gravity; and in which the action of preventing the platform descent control is carried out by the control unit which leaves or switches the solenoid valve into the non-return admission state.

[0013] According to one embodiment, to bring the solenoid valve into the non-return intake state, the control unit stops electrically supplying the solenoid valve so that the solenoid valve is returned to the non-return intake state.

[0014] According to one embodiment, the solenoid valve is of the proportional control type.

[0015] According to one embodiment, the control unit is configured to, when the measured pressure value falls below the minimum threshold value, also prevent the chassis of the machine from moving on the ground.

[0016] According to one embodiment, the hydraulic cylinder system comprises at least one single-acting hydraulic cylinder.

[0017] According to one embodiment, the control unit is also configured to: - during an upward movement of the platform, detecting an overload condition of the platform as a function of the pressure measured by the pressure sensor and the height of the platform determined using the height sensor system, and - prevent the platform from continuing to move upwards, and preferably also prevent the machine chassis from moving on the ground.

[0018] According to one embodiment, the pressure sensor system is arranged on the intake line between the solenoid valve and the hydraulic cylinder system.

[0019] According to one embodiment, the height sensor system for measuring a parameter representative of the height of the platform is an angular sensor arranged to determine an angle of inclination of a cylinder of the hydraulic cylinder system or an angle of inclination of an arm of a scissor.

[0020] According to one embodiment, the scissor system comprises several superimposed scissors, each scissor comprising a first pair of parallel arms and a second pair of parallel arms, said pairs of arms crossing each other by being articulated in their crossing zone.

[0021] The invention also relates to a method of preventing the descent of a platform of a machine according to any one of the preceding embodiments, in which the method comprises the following steps: - measure the pressure in the hydraulic cylinder system and the height at which it locates the platform; - compare the measured pressure value with a minimum pressure threshold value which is defined according to the height at which the platform is located, and - when the measured pressure value is below the minimum pressure threshold value defined for the height at which the platform is located, prevent the platform from descending, the upward movement of the platform remaining controllable.

[0022] The invention also relates to a method for authorizing the descent of the platform which is in a state in which the descent of said platform is prevented following the method according to the preceding embodiment, in which the method comprises the following steps: - control, preferably by the operator using the control panel, of the raising of the platform; - removal by an external operator of the obstacle or, control, preferably by the operator using the control panel, of the movement on the ground of the chassis of the nacelle to escape an obstacle blocking the platform during descent; - authorization by the control unit for the descent of the platform. Brief description of the drawings

[0023] Other characteristics and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting and must be read in conjunction with the appended drawings, in which:

[0024] - [Fig.l] [Fig.l] is a perspective view of a scissor lift according to a method of realization of the invention;

[0025] - [Fig.2] [Fig.2] is a schematic view of a pressure sensor associated with a lifting cylinder of a scissor lift according to one embodiment of the invention;

[0026] - [Fig.3] [Fig.3] is a graph giving an example of the evolution of the value minimum pressure threshold depending on the height at which the platform is located. DETAILED DESCRIPTION

[0027] The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, the size and relative sizes of the elements may be exaggerated for clarity. Like numerals refer to like elements throughout the drawings. However, the invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so that this description is complete.

[0028] A reference throughout the specification to “an embodiment” means that a A particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the occurrence of the phrase "in an embodiment" at various locations throughout the specification does not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0029] With reference to the figures, a scissor lift is shown allowing work to be carried out while lifting people.

[0030] This nacelle 1 comprises a self-propelled (i.e. motorized) rolling chassis 2 equipped with a motor system 12 for driving the chassis 2 on the ground. The motor system 12 may be of the thermal or electric type.

[0031] At least some of the wheels are steered wheels, having a variable orientation relative to the chassis 2, to enable the nacelle 1 to be steered. The nacelle comprises a system 13 for controlling the direction of the steered wheels.

[0032] The chassis 2 carries a scissor-type lifting structure 3. The nacelle 1 comprises a platform 4 on which an operator can be present. The lifting structure 3 extends between the chassis 2 and the platform 4.

[0033] The lifting structure 3 may comprise one or more superimposed scissors 31, 32. Two of the ends of the scissors, or of the uppermost scissors in the case of a superposition of scissors, are connected to the platform 4.

[0034] The or each scissor 31, 32 comprises a first pair of arms and a second pair of arms, which cross by being articulated in their crossing zone.

[0035] In particular, the arms of one pair are parallel to each other and are articulated to the arms of the other pair. The articulation axis is located substantially halfway along the length of each arm and is perpendicular to the plane of the X formed in side view by the pairs of arms which cross.

[0036] The nacelle 1 comprises a control unit 10 which makes it possible to control the drive motor system 12 for moving on the ground, the system 13 for controlling the direction of the steered wheels and the deployment or folding of the scissor-type lifting structure 3 as detailed below.

[0037] A hydraulic cylinder system 6 is arranged with the scissors or scissors to control the pivoting of the pairs of scissors arms 31, 32 to fold or deploy the arms of the or each scissors, so as to control the descent or rise of the platform 4. The hydraulic cylinder system 6 comprises one or more hydraulic cylinders, preferably single-acting.

[0038] It can be provided that the hydraulic cylinder system 6 comprises at least one hydraulic cylinder whose cylinder body is articulated to a pair of arms of the or a scissor 31 and whose rod is articulated to the other pair of arms of the chisel or to a pair of arms of another chisel 32.

[0039] A hydraulic circuit system 5 is used to supply the hydraulic cylinder system 6. The hydraulic circuit system comprises a hydraulic pump 51, a hydraulic distributor 52, a hydraulic supply line 53 for the hydraulic cylinder system 6, and an oil reservoir 54. The hydraulic supply line 53 extends between the hydraulic distributor 52 and the hydraulic cylinder system 6. The hydraulic pump 51 is used to circulate pressurized oil in the hydraulic circuit system 5. Preferably, the pump 51 can be controlled by the control unit 10.

[0040] The hydraulic distributor 52 is configured to, preferably using a solenoid valve included in the hydraulic distributor 52, authorize or prevent the passage of oil in the supply line 53. The hydraulic distributor 52 can be controlled by the control unit 10 to authorize or not the pressurization of oil and therefore the supply of oil to the supply line 53. The pump 51 can be actuated by a motor which can form part of the motorization system 12 or which can be driven by the motorization system 12, or which can be a separate motor.

[0041] The steering wheel steering control system 13 may be a hydraulic system forming part of the hydraulic circuit system 5.

[0042] A solenoid valve 8 is arranged on the supply line 53 of the hydraulic cylinder system 6. The solenoid valve 8 is configured to control the oil supply to the hydraulic cylinder system 6.

[0043] The solenoid valve 8 is capable of exhibiting a non-return admission state in which the solenoid valve 8 authorizes the supply of pressurized oil into the hydraulic cylinder system 6. The solenoid valve 8 also has a non-return valve 81. The authorization of oil supply allows, when the distributor directs the pressurized oil to the supply line 53 of the hydraulic cylinder system 6, an upward movement of the platform 4 by admission of oil into the hydraulic cylinder system 6, while in this state the non-return device 81 prevents a descent of the oil.

[0044] The solenoid valve 8 is also capable of having an exhaust state allowing the descent of the oil from the hydraulic cylinder system 6 to an oil reservoir 54 of the hydraulic supply system 5, to allow downward movement of the platform 4 by gravity, the oil being able to be discharged from the hydraulic cylinder system via the solenoid valve to the oil reservoir 54.

[0045] The control unit 10 makes it possible to electrically control the solenoid valve to bring it into the desired state. According to a preferred embodiment, the non-return admission state is a default state, i.e. obtained in the absence of electrical power supply. the solenoid valve, in which the solenoid valve is returned, while the exhaust state is obtained by applying a given voltage to the solenoid valve.

[0046] The action of preventing the descent control of the platform 4 is carried out by the control unit 10 which leaves or switches the solenoid valve 8 to the non-return admission state.

[0047] According to a preferred embodiment, it may be provided, as illustrated in [Fig. 2], that the supply line 53 is also provided with a pressure limiter, and preferably a pressure smoother, mounted as a bypass from the solenoid valve 8, to prevent excess pressure from damaging the hydraulic cylinder system and to avoid jolts in the operation of the hydraulic cylinder system 6.

[0048] A pressure sensor system 7, arranged on the supply line 53, between the solenoid valve 8 and the hydraulic cylinder system 6, makes it possible to measure a pressure P7m representative of the pressure in the hydraulic cylinder system 6.

[0049] The platform 4 of the nacelle comprises a control console 41 which allows the operator to transmit to the control unit 10 instructions for controlling the movement of the chassis on the ground (forward and direction), as well as instructions for lifting or lowering the platform.

[0050] The nacelle comprises a height sensor system for determining the height of the platform relative to the chassis 2. The height sensor system is preferably implemented in the form of an angle sensor system 33 which is configured to determine the angle of an arm of a scissor. Said angle is for example measured relative to a reference value corresponding to the value of the angle of said scissor arm in the folded state of the scissor (corresponding to the lowest position of the platform relative to the chassis), so that the control unit 10 makes it possible to determine the height of the platform 4 as a function of the angle measured by the angle sensor system 33.

[0051] As detailed below, the control unit 10 makes it possible to control the hydraulic circuit system 5 to control the supply of the cylinder system 6, as a function of the pressure P7m measured by the pressure sensor 7 and the height H4 determined from the angle measurement carried out by the angle sensor 33.

[0052] Under normal operating conditions, i.e. excluding detection of abnormal pressure at the level of the jack system 6, when a raising command is transmitted by the control panel 41 to the control unit 10, the control unit 10 controls the solenoid valve 8 so that it is in the non-return intake state and the control unit 10 controls the hydraulic distributor 52 to direct the oil (pressurized by the pump 51) towards the supply line 53 on which the solenoid valve 8 is located.

[0053] Under normal conditions of use, i.e. excluding detection of abnormal pressure at the level of the jack system 6, when a descent command is transmitted by the console control unit 41 to the control unit 10, the control unit 10 controls the solenoid valve 8 to be in the exhaust state allowing the oil from the cylinder system 6 to flow back down into the supply line 53, and the control unit 10 controls the hydraulic distributor 52 to direct the oil from the supply line 53 to the reservoir 54, and controls the stopping of the pump 51.

[0054] In the solutions of the state of the art, if the platform 4 is commanded to descend while it is blocked in descending by an obstacle 9, for example a low wall, a pressure drop occurs in the supply line 53 because the solenoid valve 8 is in the exhaust state which allows the oil to return to the reservoir 54. If suddenly the obstacle 9 no longer holds the platform 4, then the platform 4 risks descending suddenly due to the pressure drop in the supply line 53 (which was previously decompressed due to the command to descend the platform which allowed the oil to escape from the jack while the platform actually remained blocked against the obstacle) which no longer allows the descent of the platform to be controlled, which risks damaging the machine and is dangerous for the operator present on the platform.

[0055] The invention makes it possible, by blocking this exhaust as soon as an abnormal drop in pressure is detected, by returning the solenoid valve 8 to the non-return admission state, to interrupt the drop in pressure and to maintain in the supply line 53 of the jack system, a pressure making it possible to retain the platform 4 in the event of sudden release of the platform 4 relative to the obstacle.

[0056] Example of operation

[0057] An example of operation is presented below. The method presented below is implemented at least when the nacelle is in working mode. It can be provided that the pressure monitoring method is only activated when the nacelle is in working mode (or position), i.e. when the height H4 of the nacelle measured by the angular sensor 33 is greater than a given threshold value, as opposed to a so-called transport mode (or transport position) where the platform is lowered i.e. less than a given threshold value. Alternatively, it can be provided that the method is implemented regardless of the operating mode of the machine.

[0058] The control unit 10 compares, preferably in real time, i.e. at a given frequency of 100 Hz, for example, the pressure measured P7m by the pressure sensor system 7, with a defined threshold value P7s for the height H4 at which the platform 4 is located and which is measured using the angular sensor 33.

[0059] When the measured pressure P7m is lower than the threshold value P7s, called the minimum value, defined for said height H4, then it is considered that the platform 4 is blocked in descent, and the descent movement of the platform 4 is blocked.

[0060] Such a case of “drop” in pressure may result from a phase of descent of the platform 4 controlled by the operator when, during the descent, platform 4 presses against an obstacle. But this case of blocking could also occur when the platform stops if a landslide occurs under the nacelle, and the platform thus finds itself pressing against a low stop formed by an obstacle, such as a low wall.

[0061] When a command, in normal operating conditions of the machine, is given to lower the platform 4, the solenoid valve 8 is in an open position allowing the oil from the hydraulic cylinder system 6 to return to the reservoir 54. The pressure P7m in the hydraulic cylinder system 6, which is in communication with the line 53, then decreases until it falls below the minimum threshold value P7s because the weight of the platform 4 is taken up by the obstacle 9 while the solenoid valve 8 is in the open state. As a result, the control unit 10 detects a pressure P7m lower than the minimum threshold value P7s (low pressure limit), and controls the automatic stopping of the descent by putting the solenoid valve 8 in the closed state. Preferably, the control unit 10 then triggers an alert. According to a preferred aspect, the control unit 10 also triggers the prohibition of movement on the ground of the machine.

[0062] According to a preferred embodiment, to control the automatic stopping of the descent, the control unit 10 then controls the passage of the solenoid valve 8 into the non-return intake state. It can be provided that the solenoid valve 8 is automatically returned to this non-return intake state in the absence of current. In this case, it is thus sufficient for the control unit to control the stopping of the supply of the solenoid valve 8 to obtain its passage into the non-return intake state.

[0063] In the non-return intake state, the non-return device 81 is active and prevents the descent of oil from the cylinder system 6 to the reservoir 54, so that the oil pressure in the supply line 53 is maintained and the cylinder system supports the platform 4. In the non-return intake state, the solenoid valve 8 allows the passage of oil from the hydraulic distributor 52 to the cylinder system 6, which allows an upward movement of the platform. The user can thus, from the control panel 41, send an upward control instruction to the control unit 10 which can then control the actuation of the pump 51 and control the hydraulic distributor 52 to direct the oil pressurized by the pump 51 to the supply line 53.Alternatively, but less economically, it could be provided that the pump 51 is permanently activated and that the control unit 10 simply controls the hydraulic distributor 52 to direct the oil to 53.

[0064] The upward control of the platform 4 makes it possible to no longer be supported on the obstacle and, due to the rise in pressure in the supply line 53, to authorize the movement of the machine on the ground again, to allow the operator to order a movement on the ground of the machine to escape the obstacle, and thus allow, once the machine has been moved on the ground away from the obstacle, to order a descent of the platform (which is then authorized due to the rise in pressure as indicated above). It is also possible to provide, for example in the case where the obstacle is a wooden board that can be moved by an operator outside, that the raising of the platform is sufficient to clear the basket from the obstacle without having to move the basket on the ground.

[0065] Thus, when the control unit 10 prevents the platform 4 from descending following the detection of a pressure drop at the level of the jack system 6, the operator can only activate the platform lifting control as a command for moving the platform. Preferably, in this case of blocking the descent, the control unit is configured to authorize the ascent but with a reduced lifting speed and / or acceleration (ascent), to avoid jolts and shocks, which could be dangerous for the operator and the machine.

[0066] According to a preferred embodiment of the invention, the control unit 10 is also configured to: - during an upward movement of the platform 4, detecting an overload condition of the platform 4 as a function of the pressure measured by the pressure sensor 7 and the height of the platform 4 determined using the height sensor system 33, and - prevent the platform 4 from continuing to move upwards, and preferably also prevent the chassis 2 of the machine from moving on the ground.

[0067] The movement prevention(s) resulting from overload detection are maintained as long as the pressure does not fall below the maximum pressure value defined for the height at which the platform is located. The return of the pressure below an acceptable threshold value can be obtained by a command to lower the platform 4 by the operator using the control panel 4L

[0068] Thus, when the pressure sensor 7 and the solenoid valve 8 are already present in the original machine to manage an overload case, these components can also be used to detect an “underload” or pressure drop and, thanks to the control unit 10, manage such a situation resulting from a blockage of the platform against an obstacle 9. Thus, the pressure sensor 7 and the solenoid valve 8 are, thanks to the configuration of the control unit 10 according to the invention, used to also manage a case of pressure drop in the cylinder line 53 resulting from a descent command of the platform 4 while the platform 4 is blocked in descent against an obstacle 9. Such a design thus makes it possible to obtain safety not only when ascending but also when descending with respect to an obstacle reliably and without adding components.

[0069] The control unit is presented for example in the form of a processor and a data memory in which computer instructions executable by said processor are stored, or in the form of a microcontroller.

[0070] In other words, the functions and steps described can be implemented in the form of a computer program or via hardware components (e.g. programmable gate arrays). In particular, the functions and steps operated by the control unit, in particular for controlling the movement system 12, the steering system 13, and the hydraulic circuit system 5, can be carried out by instruction sets or computer modules implemented in a processor or controller or be carried out by dedicated electronic components or components of the programmable logic circuit type (or FPGA which is the acronym for field-programmable gate array, which literally corresponds to in-situ programmable gate array) or of the application-specific integrated circuit type (or ASIC which is the acronym for application-specific integrated circuit, which literally corresponds to application-specific integrated circuit).It is also possible to combine computer parts and electronic parts.

[0071] The control unit is thus an electronic and / or computer unit. When it is specified that said unit is configured to carry out a given operation, this means that the unit comprises computer instructions and the corresponding execution means which make it possible to carry out said operation and / or that the unit comprises corresponding electronic components.

[0072] The invention is not limited to the embodiments illustrated in the drawings.

[0073] Furthermore, the term "comprising" does not exclude other elements or steps. Furthermore, features or steps that have been described with reference to one of the embodiments set forth above may also be used in combination with other features or steps of other embodiments set forth above.

[0074] As explained above, measuring the pressure in the hydraulic cylinder system during the descent of the platform makes it possible to detect, when the measured pressure P7m is lower than a given threshold value P7s depending on the height H4 of the platform, that the platform is at its bottom stop against an obstacle, such as a low wall, and to then trigger the stopping of the descent movement and preferably to prevent the machine from moving on the ground. In particular, the stopping can be obtained by placing the solenoid valve 8 in the non-return admission state for which the solenoid valve 8 allows the oil to pass from the distributor 52 to the cylinder system 6 and has a non-return valve 81 which prevents the oil from going back down from the cylinder system 6, which prevents the descent of the platform.

[0075] Such a design not only makes it possible to avoid having to add components in the scissor lift (which is usually equipped with a pressure sensor and a solenoid valve on the supply line of the jack system), such as a strain gauge as in certain state-of-the-art solutions, but also to benefit from greater reliability in detecting descent blockage compared to a solution using a strain gauge.

Claims

Claims

1. A person handling machine, called a nacelle (1), which comprises - a rolling chassis (2) equipped with a system (12) for driving the chassis (2) on the ground; - a platform (4) on which an operator is able to climb, and a control desk (41); - a lifting structure (3) which extends between the chassis (2) and the platform (4); the lifting structure (3) comprising a scissor system (31, 32) capable of moving from a folded position in which the platform (4) is in the lowered position to a deployed position in which the platform (4) is in the raised position, and vice versa; - a height sensor system (33) for measuring a parameter representative of the height of the platform (4); - a hydraulic cylinder system (6) configured to control the folding and deployment of said scissor system (31, 32); - a hydraulic circuit system (5) comprising: - a hydraulic distributor (52), and - a hydraulic pump (51) for supplying pressurized oil to the hydraulic distributor (52), - a hydraulic supply line (53) connected to the hydraulic distributor (52) and to the hydraulic cylinder system (6), and a solenoid valve (8) configured to control the oil supply to the hydraulic cylinder system (6); - a pressure sensor system (7) arranged to measure a pressure representative of the pressure in the hydraulic cylinder system (6); - a control unit (10) configured to, from control instructions transmitted by the control panel (41), control the hydraulic circuit system (5) to move the platform (41) up or down: characterized in that the control unit (10) is also configured to, at least when the nacelle is in a working position which is detected by the control unit (10), when the height of the platform is greater than a given value: - compare the measured pressure value (P7m) to a minimum threshold value (P7s) which is defined as a function of the height (H4) at which the platform (4) is located, and - when the measured pressure value (P7m) is below the minimum threshold value (P7s) defined for the height (H4) at which the platform (4) is located, prevent the platform (4) from descending, the upward movement of the platform (4) remaining controllable.

2. Machine according to claim 1, in which the solenoid valve (8) is capable of having: - a non-return admission state in which the solenoid valve (8) authorizes the supply of pressurized oil into the hydraulic cylinder system (6), the solenoid valve (8) having a non-return valve; - and an exhaust state authorizing the descent of the oil from the hydraulic cylinder system (6) to an oil reservoir (54) of the hydraulic circuit system (5), to allow downward movement of the platform (4) by gravity; and in which the action of preventing the descent control of the platform (4) is carried out by the control unit (10) which leaves or switches the solenoid valve (8) into the non-return admission state.

3. Machine according to claim 2, wherein, to bring the solenoid valve (8) into the non-return intake state, the control unit (10) stops electrically supplying the solenoid valve (8) so that the solenoid valve (8) is returned to the non-return intake state.

4. Machine according to any one of the preceding claims, in which the solenoid valve (8) is of the proportional control type.

5. Machine according to any one of the preceding claims, in which the control unit (10) is configured to, when the measured pressure value (P7m) falls below the minimum threshold value (P7s), also prevent the chassis (2) of the machine from moving on the ground.

6. Machine according to any one of the preceding claims, in which the hydraulic cylinder system (6) comprises at least one single-acting hydraulic cylinder.

7. Machine according to any one of the preceding claims, in which the control unit (10) is also configured to: - during an upward movement of the platform (4), detect an overload condition of the platform (4) as a function of the pressure measured by the pressure sensor (7) and the height of the platform (4) determined using the height sensor system (33), and - prevent the platform (4) from continuing to move upwards, and preferably also prevent the chassis (2) of the machine from moving on the ground.

8. Machine according to any one of the preceding claims, wherein the pressure sensor system (7) is arranged on the intake line (53) between the solenoid valve (8) and the hydraulic cylinder system (6).

9. Machine according to any one of the preceding claims, in which the height sensor system (33) for measuring a parameter representative of the height (H4) of the platform (4) is an angular sensor (33) arranged to determine an angle of inclination of a cylinder of the hydraulic cylinder system (6) or an angle of inclination of an arm of a scissor (31, 32).

10. Machine according to any one of the preceding claims, in which the scissor system (31, 32) comprises several superimposed scissors (31, 32), each scissor (31, 32) comprising a first pair of parallel arms and a second pair of parallel arms, said pairs of arms crossing each other by being articulated in their crossing zone.

11. A method for preventing the descent of a platform (4) of a machine (1) according to any one of the preceding claims, wherein the method comprises the following steps: - measuring the pressure (P7m) in the hydraulic cylinder system (6) and the height (H4) at which the platform (4) is located; - comparing the measured pressure value (P7m) with a minimum pressure threshold value (P7s) which is defined as a function of the height (H4) at which the platform (4) is located, and - when the measured pressure value (P7m) is below the minimum pressure threshold value (P7s) defined for the height (H4) at which the platform (4) is located, preventing the descent of the platform (4), the upward movement of the platform (4) remaining controllable.

12. Method for authorizing the descent of the platform (4) which is in a state in which the descent of said platform is prevented following the method according to claim 11, in which the method comprises the following steps: - control, preferably by the operator using the control panel (41), of the ascent of the platform (4); - removal by an external operator of the obstacle (9) or, control, of preferably by the operator using the control panel (41), the movement on the ground of the chassis (2) of the nacelle to escape an obstacle (9) blocking the platform (4) on descent; - authorization by the control unit (10) of the descent of the platform (4).

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