EP3556710B1

EP3556710B1 - Crane with articulated arm

Info

Publication number: EP3556710B1
Application number: EP19153039.3A
Authority: EP
Inventors: Ivan MAFFEIS; Valentino Birolini; Roberto Signori; Rossano Ceresoli
Original assignee: FASSI GRU SpA
Current assignee: FASSI GRU SpA
Priority date: 2018-04-19
Filing date: 2019-01-22
Publication date: 2023-01-11
Anticipated expiration: 2039-01-22
Also published as: FI3556710T3; PL3556710T3; IT201800004717A1; DK3556710T3; EP3556710A1

Description

Technical field of the invention

The present invention refers to a crane with articulated arm, such as an articulated crane or an elevating work platform (EWP), provided with a system for compensating deformations caused by applied loads. The term "articulated arm" generally means a system provided with a plurality of bodies consecutively connected to each other in order to form an open kinematic chain having a plurality of translative and/or rotative degrees of freedom in the space.

Prior art

Referring for example to the articulated cranes, these generally have a vertically rotative column, a main arm rotative with respect to the column, one or more secondary arms provided with extensions. The free end of the last extension of the secondary arm is commonly known as end-effector. A hook for hoisting loads or, in case of an EWP, a basket for lifting persons could be for example associated to the end-effector.
A typical example of such crane is disclosed in document EP3239092A1 which shows a hydraulic crane having a column and an articulated boom with plurality of bodies consecutively connected, one or more first sensors associated to the respective bodies and a control unit.
Due to the load applied at the end-effector, the articulated arm is subjected to elastic deformations which disappear when the load is removed. Consequently, sometimes the end-effector could be subjected to height variations because a load is added or removed from it.
With reference to a crane, the above described condition can be dangerous. It is cited the case, for example, of a yard crane operated for moving materials into a recess. As soon as the crane unloads the materials, the elastic deformation of the arm disappears, consequently the crane can hit the structure where the recess is located. Now it is made reference to an EWP, the load thereof being composed by one or more persons contained in a basket. If the basket is positioned at a right height for enabling these persons to easily descend, as soon as the basket is empty, it moves up to a higher level. Consequently, the persons will not be capable to get up again on the basket because it is at this higher level.
In order to solve the above cited problems, it is known to measure the structural deformations of the arms, for example by strain gauges. In this way it is possible to compensate the variations of height of the end-effector, caused by such deformations. However, such compensation technique is inaccurate because it does not allow for other factors, such as for example the mounting allowances of the extensions, which do not cause substantial deformations in the bodies of the articulated arm, but they anyway modify the actual height of the end-effector when is loaded. Neither it is possible to consider the contribution of each pair of subsequent extensions to the height variation of the end-effector. For example, when one extension is completely outside the preceding extension, said allowances will have a greater impact on the height variation of the end-effector than a pair of extensions wherein an extension is just partially outside the preceding extensions.
Further prior art embodiments are disclosed in documents CN103 206 090 , WO 2010/045602 A1 , WO 2013/006625 A2 , DE 20 2013 003782 U1 , JP S57 1195 A .

Summary of the invention

Therefore, it is an object of the present invention to provide a crane with articulated arm, such as an articulated crane or an EWP, which is capable of overcoming the inconveniences cited with reference to the prior art, particularly which enables to control height variations of the end-effector determined by load variations of the end-effector in a sufficiently accurate way.
This and other objects are obtained by a crane with articulated arm according to claim 1.
The dependent claims define possible advantageous embodiments of the invention.

Brief description of the figures

In order to have a better comprehension of the invention and appreciate the advantages thereof, some exemplifying non-limiting embodiments thereof will be described in the following with reference to the attached figures, wherein:

Figure 1 is a side view of an articulated crane;
Figure 2 is a schematic illustration of an articulated arm and of possible modes for compensating deformations caused by loads.

Detailed description of the invention

The present description will illustratively refer to an articulated crane. Anyway, the articulated crane can be of a different type, for example can be a robotic arm or an elevating work platform (EWP).
With reference to the attached Figure 1, it shows an example of a possible crane with articulated arm, particularly an articulated crane, for example a "hydraulic loader crane" generally indicated by reference 101.
The crane 101 comprises a column 102 rotative with respect to a stationary reference about its own axis, and one or more possibly extendable arms 103', 103". The possibility of extending the arms, if provided, is obtained by a plurality of extensions 104 translatingly movable from each other in order to modify the axial length of the corresponding arm. In the example in Figure 1, just the secondary arm 103" can be lengthened by actuating the extensions 104. In the following description, the first arm 103', devoid of extensions, is termed "main arm", while the secondary arm 103", provided with the extensions 104, will be termed "secondary arm". The free end 105 of the last extension of the secondary arm 103", in other words of the last body of the kinematic chain, is commonly termed end-effector. A hook 106 actuatable by a rope winch 107 can be provided at the end-effector 105, for example. If the articulated arm is an EWP, the hook can be substituted with a basket (not shown in the figures), for hoisting persons, for example.
The crane 101, according to the shown example, without considering the degree of freedom of the hook 106 or basket, consequently, has the following degrees of freedom:

1) rotation of the column 102 about the axis thereof;
2) rotation of the main arm 103' with respect to the column 102 about an axis perpendicular to the plane on which the column 102 and main arm 103' lie;
3) rotation of the secondary arm 103" with respect to the main arm 103' about an axis perpendicular to the plane on which the main arm 103' and secondary arm 103" lie;
4) translations of the extensions 104 with respect to the secondary arm 103".

Consequently, the above described crane implements an open kinematic chain, with a plurality of consecutively connected bodies (column, main arm, secondary arm, extensions) and a free end (end-effector 105). Generally, the end-effector 105 is the point of the kinematic chain wherein the load transported by the articulated arm itself is applied.
Each above cited degree of freedom is matched by the movement of an element of the articulated arm with respect to another (degrees of freedom 2, 3, 4) or with respect to a reference (degree of freedom 1). The crane 101 is provided with a plurality of actuators, particularly at least one actuator corresponding to a determined degree of freedom, for executing such movements. With reference to Figure 1, a first hydraulic jack 108, moving the main arm 103' with respect to the column 102, a second hydraulic jack 109, moving the secondary arm 103" with respect to the main arm 103', and an actuator 110 for moving the column 102 with respect to the stationary reference are shown, for example. Then, further actuators will be provided (not shown in the figures) for example of a hydraulic type, for moving the extensions 104. Obviously, even though the actuators of the cranes are usually of a hydraulic type, generally it is possible to provide actuators of a different type (electric or pneumatic, for example) for the articulated arms.
The crane 101 comprises a plurality of sensors adapted to measure an angle or a linear extension of a body of the kinematic chain, with respect to the preceding body of the chain or with respect to a stationary reference. Preferably, the first sensors are selected and positioned to obtain measurements which enable to determine the theoretical absolute coordinates of the end-effector 105, particularly the Cartesian coordinates thereof with respect to a stationary reference. For example, if the origin of a reference Cartesian system coincides with the base of the column 102, the theoretical absolute coordinates of the end-effector 105 can be expressed by the three values x, y, z.
With reference for example to the crane 101, the plurality of first sensors can include:

1) an angular sensor for measuring the rotation of the column 102 about the axis thereof with respect to a stationary reference (which can be the ground, for example);
2) an angular sensor for measuring the rotation of the main arm 103', for example, for measuring the absolute angle included between the main arm 103' and horizontal;
3) an angular sensor for measuring the rotation of the secondary arm 103", for example, for measuring the absolute angle included between the secondary arm 103" and horizontal;
4) one or more linear sensors for measuring the projection of the extensions 104 with respect to the secondary arm 103".

As a function of where the first sensors are positioned, they can include linear or angular encoders, magnetostrictive sensors, inertial platforms or similar, for example. From the signals of the above cited first sensors, it is possible, by geometrical relationships, to determine the theoretical absolute coordinates of the end-effector 105. As it will be more clearly explained in the following, such coordinates are termed "theoretical" since they do not consider the deformations of the bodies forming the kinematic chain, or, in other words, they consider such bodies as they were perfectly rigid bodies.
Moreover, it is observed that, according to a possible embodiment, the first sensors can be selected and positioned in order to obtain measurements which enable to determine only the theoretical height of the end-effector 105, for example the theoretical absolute coordinate y.
Advantageously, the articulated arm 101 further comprises at least one second absolute angular sensor placed in proximity of or at the end-effector 105. Such second absolute angular sensor is particularly capable of measuring an absolute inclination angle with respect to a stationary reference, of a segment of the body of the articulated arm on which the end-effector 105 lies. The absolute inclination of the body on which the end-effector 105 lies, can be measured with respect to the horizontal (or vertical), for example. With reference to the example of Figure 1, such sensor will measure, e.g. the absolute angle included between a line joining the point connecting the secondary arm 103" to the first movable extension, and the end-effector 105, with respect to the horizontal, for example. The second absolute angular sensor can comprise, for example, an inertial sensor capable of measuring a rotation angle between the gravity, which is per se perfectly vertical, and an acceleration lying on a reference line rotating with respect to the vertical.
For gaining a better comprehension of the beforehand description, reference is made to the example shown in Figure 2 schematically illustrating an articulated arm 101, with a column 102 (schematically shown in the example as perfectly vertical, even though physically it can have a certain inclination angle with respect to the vertical) of length a, a main arm 103' of length b and rotative with respect to the column 104, and a secondary arm 103" rotative with respect to the main arm 103' and of length c, wherein the main arm further comprises one or more extensions 104 which can project of a varying amount Δd from the secondary arm 103". The sensors of the articulated arm comprise a sensor for measuring an absolute angle α of the main arm 103', a sensor for measuring an absolute angle β of the secondary arm 103", a sensor for measuring the linear projection Δd of the extensions 104 from the secondary arm 103", and the second absolute angular sensor for measuring the absolute angle γ of the extensions 104, at the end thereof the end-effector 105 is placed. For the sake of the comprehension, the above cited angles are referred to the horizontal. Figure 2 shows a pair of Cartesian axes x-y, the origin thereof conventionally coincides with the base of the column 102.
Moreover, it is observed that a rotation sensor of the column 102 with respect to a stationary reference (axis z of the pair x-y not shown in the figures) can be provided, which however is not relevant for determining the height of the end-effector.
The theoretical height y₁₀₅ of the end-effector 105, in other words the height the end-effector 105 could reach without deformations caused by loads, is obtainable by the following relationships, detectable by measures from the above cited first angular and linear sensors: $y_{105} = a + b \cdot \sin α + (c + Δ d) \cdot \sin β$
The second absolute angular sensor at the end-effector 105 would theoretically measure an angle γ equal to β without any deformations.
Anyway, in the presence of a load at the end-effector 105, the extensions 104 will inflect (broken line) due to the deformations and allowances in the joints, particularly in the extensions, and the end-effector 105 will reach an effective height y₁₀₅* less than the theoretical height y₁₀₅, so that the second absolute angular sensor will measure an angle γ less than β.
Consequently, it is possible to estimate the height variation Δy of the end-effector 105, particularly the height reduction thereof, by measuring β and γ. An approximate estimate of the height variation Δy can be obtained by the following relationship, for example: $Δ y \approx Δ d \cdot (β - γ)$
if the angles are expressed in radiants. Obviously, possible estimates of the height reduction Δy based on geometrical relationships different from the above discussed linear approximation are foreseeable.
From the above given description, it is understood that, for just determining the height variation Δy of the end-effector 105, are only required the absolute sensor for measuring the absolute angle γ, the sensor for measuring the angle β, the sensor for measuring the linear projection Δd of the extension 104. The sensor for measuring the angle α is not required for estimating the height variation Δy but is required for determining the theoretical and actual absolute coordinates of the end-effector 105.
It is observed that the example shown in Figure 2 assumes that the substantial deformations can only form in the segment on which the extensions 104 lie. However, further deformations can obviously happen. For example, in the case shown in Figure 2, also the main arm 103' can be subjected to deformations, which in turn impact the actual height of the end-effector 105. If it is desired to take into account also these deformations, a further absolute angular sensor on the main arm 103', preferably in proximity of the joint of the secondary arm 103", could be provided.
The articulated arm 101 therefore comprise one or more further second absolute angular sensors associated to the bodies forming the open kinematic chain, arranged at or in proximity of the joints of the following body of the kinematic chain. For example, such second additional absolute angular sensors can be provided at least on the bodies implementing linear relative movements since these latter are more susceptible to deformations due to the joints. Referring again to the example of a crane of Figure 1, if also the main arm 103' were provided with extensions, it would be possible to provide a further absolute angular sensor at the last extension in proximity of the rotative joint for connecting the secondary arm 103".
The articulated arm 101 comprises a control unit operatively connected to the actuators, for moving them, and to the above cited first and second sensors, for receiving signals indicative of the above given magnitudes.
The control unit is configured to:

determine a theoretical height of the end-effector 105 based on signals from the plurality of the first sensors;
estimate a height variation of the end-effector 105 between the theoretical height and an actual height caused by loads applied to the arm, based on signals from the plurality of first sensors and from at least one second absolute angular sensor;
command the actuators to reduce the estimated height variation of the end-effector 105.

Compensating the difference between the theoretical height and actual height can be differently performed according to the circumstances. Moreover, it can be performed both when the end-effector is still and when the same is moving.
For example, when a crane is still, the following situations can occur:

1) increase of the end-effector height when a load is removed;
2) decrease of the end-effector height when a load is applied.

In the case 1), desirably, the end-effector 105 should remain at the same height even though a load is removed. Such condition occurs for example when the transported persons are consecutively descending from the basket of an EWP, so that the basket gradually moves up as the persons get down. Consequently, the control unit can be configured to operate the actuators in order to hold the end-effector at the actual height estimated in the presence of the load, also when the load is removed because the unloaded end-effector would tend to return to the theoretical height.
In the case 2), desirably the end-effector 105 should be held at the same height as the one it had in an unloaded condition even though the load is applied. For example, such condition can occur when an unloaded arm is introduced inside a recess and it is desired to prevent it from impacting the walls of the recess when it is loaded. Therefore, the control unit can be configured to operate the actuators for holding the end-effector in the position corresponding to the theoretical absolute coordinates of a loaded condition when the end-effector would tend to move down.
Another possibility consists of compensating the deformations when the crane is moving.
For example, it is possible to impart the movement by supplying a sequence of absolute coordinates of the end-effector to the control unit. The movement instructions can be imparted by providing a user interface device connected to the control unit, in order to enable an operator to manually move the crane and possibly to gain access to other functions. For example, the user interface device can comprise a remote control and the control unit can comprise a transmission module for communicating with this latter (a radio transmission module, for example). The absolute coordinate sequence can be directly set by the operator or a previously performed stored movement sequence can be repeated.
Advantageously, the operator can also activate or deactivate the compensation of the deformation by the user interface device.
Advantageously, the control unit is configured to act on the actuators so that the end-effector 105 follows a trajectory intercepting the points set as the desired coordinates. Preferably, in this case, operative predefined logics are generally provided, so that the control unit selects which actuators must be operated for performing a certain desired movement of the end-effector. For example, an actuation logic can be one which minimizes the oil flow rate or the hydraulic power required to operate the actuators. A further logic can be one of the minimum distance travelled by the end-effector for arriving to a desired position. A further often used criterion, for example in combination with one of the above cited criteria, consists of holding the actuators away from the stop position. The predetermined operative logics are per se known and therefore they are not specifically described.
When the crane is moved by the preset sequence of motions having the Cartesian coordinates which must be followed by the end-effector, if a load is applied, the end-effector tends to follow a trajectory at a height lower than the set one, due to deformations caused by the load itself.
Consequently, the control unit is advantageously configured to monitor, for each coordinate of the predefined sequence, the actual height of the end-effector, estimated according to said modes, and to act on the actuators for taking the end-effector to the theoretical height, which is the height corresponding to the absolute coordinates set by the operator.
In the present description and in the attached claims it is observed that the control unit, and the elements indicated by the term "module", can be implemented by hardware devices (central units, for example), by software or by a combination of hardware and software.
From what was hereinbefore discussed, a person skilled in the art can appreciate that the articulated arm of the crane, according to the invention, can be moved by means of a Cartesian coordinate logic and that it is possible to compensate, both under static and dynamic conditions, the height reduction of the end-effector caused by applied loads.
A person skilled in the art, in order to meet specific contingent needs, could introduce several additions, modifications, or substitutions of elements with other operatively equivalent, to the described embodiments, without falling out of the scope of the attached claims.

Claims

Crane with articulated arm, the articulated arm (101) comprising:
- a plurality of bodies consecutively connected in order to form an open kinematic chain with an end-effector (105), having a plurality of translative and/or rotative degrees of freedom and a plurality of actuators for moving said bodies;

- one or more first sensors associated to said bodies, adapted to supply signals indicative of linear or angular positions of the bodies of the kinematic chain in order to enable to determine a theoretical height of the end-effector (105);

- at least one second absolute angular sensor adapted to measure an absolute angle of the body of the kinematic chain where the end-effector (105) is located, and to provide a signal indicative of the same;

- a control unit operatively connected to said actuators, to said one or more first sensors, and to said at least one second absolute angular sensor, configured to:

- determine said theoretical height of the end-effector (105) based on the signals from the one or more first sensors;

- estimate a height variation of the end-effector (105) between the theoretical height and an effective height determined by loads applied to the arm based on signals from the one or more first sensors and from the at least one second absolute angular sensor;

- commanding the actuators to reduce the estimated height variation of the end-effector (105), said articulated crane comprises a column (102) rotatable around its axis, said plurality of bodies comprises
a main arm (103') rotatable with respect to the column (102), a secondary arm (103") rotatable with respect to the main arm (103') and comprising at least one extension translatingly extendable with respect to the secondary arm itself, and said one or more first sensors comprise one angular sensor for measuring the rotation of the main arm (103'), one angular sensor for measuring the rotation of the secondary arm (103"), one linear sensor for measuring the translation of the at least one extension (104) with respect to the secondary arm (103"), and said at least one second absolute angular sensor is disposed on the at least one extension (104) of the secondary arm (103') in proximity of or at the end-effector (105).
Crane with articulated arm (101) according to claim 1, wherein said control unit is configured so that said step of commanding the actuators to reduce the estimated height variation of the end-effector (105) comprises commanding the actuators to hold the end-effector (105) at the estimated effective height in the presence of a load applied upon removing said load.
Crane with articulated arm (101) according to claim 1 or 2, wherein said control unit is configured so that said step of commanding the actuators to reduce the estimated height variation of the end-effector (105) comprises commanding the actuators to hold the end-effector (105) at the theoretical height upon applying a load.
Crane with articulated arm (101) according to anyone of the preceding claims, wherein said control unit is configured so that said step of commanding the actuators to reduce the estimated height variation of the end-effector (105) is performed when the articulated arm is still.
Crane with articulated arm (101) according to anyone of the preceding claims, wherein said control unit is configured to move the articulated arm according to a sequence of predetermined absolute coordinates of the end-effector (105), the control unit being further configured to command the actuators to reduce the estimated height variation of the end-effector in each predetermined absolute coordinate of the sequence of the predetermined absolute coordinates.
Crane with articulated arm (101) according to anyone of the preceding claims, further comprising one or more additional second absolute angular sensors associated to the bodies forming the kinematic chain, wherein said control unit is operatively connected to said additional second absolute angular sensors and is configured to estimate the height variation of the end-effector between the theoretical height and the effective height determined by loads applied to the arm further based on the signals from the additional second absolute angular sensors.
Crane with articulated arm (101) according to anyone of the preceding claims, further comprising a user interface device communicating with the control unit and configured to activate and deactivate the step of commanding the actuators to reduce the estimated height variation of the end-effector (105).
Crane with articulated arm (101) according to anyone of the preceding claims, wherein said one or more first sensors comprise an absolute angular sensor adapted to measure an absolute angle of a body of the kinematic chain with respect to a reference, and/or a linear sensor adapted to measure the linear extent of one or more of said bodies with respect to the preceding body of the kinematic chain.
Crane with articulated arm (101) according to anyone of the preceding claims, wherein said articulated arm (101) comprises an elevating work platform (PLE).