Device and a process for controlling a swinging of a load suspended from a lifting apparatus

Abstract

A device for controlling a swinging of a load suspended from a motorized slidable element is described. The controlling device includes a control unit and an inertial platform. The control unit is provided with means to measure and control the speed of the motorized slidable element and is able to process the values representative of the inclination angle of the cable with respect to the vertical to calculate and to impart control actions in order to dynamically control the speed of the motorized slidable element as a function of a desired inclination angle of the cable with respect to the vertical.

Claims

1. A device for controlling a swinging of a load suspended from a motorized slidable element which can move along a substantially horizontal axis, the controlling device comprising a control unit and an inertial platform, the inertial platform being able to detect representative values of an inclination angle of a cable that supports the load with respect to the vertical and being provided with means for communicating the values to the control unit, wherein the control unit is provided with means to measure and control the speed of the motorized slidable element and is able to process the values representative of the inclination angle of the cable with respect to the vertical so as to calculate and to impart control actions in order to dynamically control the speed of the motorized slidable element as a function of a desired inclination angle of the cable with respect to the vertical and wherein the control unit comprises a gain scheduled proportional controller provided with means to calculate a variable gain to be applied to the control of the speed of the motorized slidable element as a function of a distance of the load from the motorized slidable element, the distance being comprised between a maximum and a minimum value, the variable gain being calculated as a function of the distance of the load from the motorized slidable element.

2. The device of claim 1, wherein the inertial platform is able to detect the inclination angles of the cable that supports the load with respect to the vertical in two reciprocally perpendicular oscillation directions defining sliding axes for respective motorized sliding elements and the control unit is able to process the values with the aim of calculating and imparting motor control actions as a function of a desired inclination angle of the cable with respect to the vertical.

3. The device of claim 1, wherein the control unit imparts the calculated control actions to the motors by commanding, for each motor, a respective inverter which regulates the velocity of the motor to which it is associated.

4. The device of claim 1, wherein the inertial platform comprises an accelerometer and a gyroscope.

5. The device of claim 1, wherein the inertial platform is positioned at a fixed head of the cable which supports a load gripping element.

6. The device of claim 1, wherein a remote processing unit can be associated to the control unit.

7. A process for control of swing of a suspended load by means of motorized slidable elements, comprising the following steps: monitoring a representative value of an inclination angle of a cable that supports the load with respect to the vertical; determining a difference between the monitored inclination angle and a desired inclination angle so as to reduce or eliminate the difference; calculating the action of control to be applied to at least one of the motors of the motorized slidable elements; applying the control action to at least one of the motors of the motorized slidable elements as a function of a desired inclination angle of the cable with respect to the vertical; and calculating a variable gain to be applied to the control of the speed of the motorized slidable element as a function of a distance of the load from the motorized slidable element, the distance being comprised between a maximum and a minimum value, wherein the calculation is performed by means of a gain scheduled proportional controller and wherein the variable gain is calculated as a function of the distance of the load from the motorized slidable element.

8. The process of claim 7, wherein the step of monitoring a value representing the inclination angle is done with the use of an inertial platform.

9. The process of claim 7, wherein the step of calculating the control action to be applied to at least one of the motors of the motorized slidable elements is carried out on the basis of a mathematical model which takes account of the representative value of the monitored inclination angle and the variation thereof over time.

10. The process of claim 7, wherein the calculating step of the control action is carried out taking account of variations in the distance of the load from the sliding element.

11. The process of claim 7, wherein the calculating step and the applying step of the calculated control action are carried out independently for each of the motors of the sliding elements, by commanding respective inverters.

12. A control apparatus for a lifting apparatus comprising a control unit, a memory and a computer program, stored in the memory, the computer program carrying out, when executed, the process of claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further characteristics and advantages of the invention will emerge from a reading of the description that follows, provided by way of non-limiting example, with the aid of the figures of the accompanying drawings.

(2) FIG. 1 is a perspective view of a bridge crane to which the control device is applied according to an embodiment of the present invention;

(3) FIG. 2 is a schematic view of the bridge crane of FIG. 1;

(4) FIG. 3 is a schematic view of embodiments of the control device of the invention;

(5) FIG. 4 is a schematic view of some relevant parameters for the control system of the invention;

(6) FIG. 5 illustrates a block diagram relating to the architecture of an embodiment of the control system;

(7) FIG. 6 illustrates a measuring element of the parameters describing the motion of a load;

(8) FIG. 7 is a schematic view, in a single dimension, of some relevant parameters for the control system of the invention; and

(9) FIG. 8 illustrates a block diagram relating to the architecture of a further embodiment of the control system.

DESCRIPTION OF THE DRAWINGS

(10) The present invention relates to a device and a procedure for controlling oscillation of a load suspended by means of cable or chain lifting equipment, such as bridge cranes, tower cranes for construction, mobile cranes and similar apparatus for lifting and moving loads. For the sake of simplicity, it will be described with reference to a bridge crane.

(11) FIG. 1 schematically illustrates a bridge crane 10 exhibiting a bridge 19 comprising two mutually parallel beams 15,16, the bridge 19 being mobile along a first direction denoted in FIG. 1 by X, which movement is achieved by the movement of the two heads 13,14 along two beams 33,34.

(12) A motorized carriage 20 is mounted on the bridge 19, which carriage can slide on two rails 15, 16, each located on a respective beam 15, 16 of the bridge 19. The carriage 20 can slide along a perpendicular direction to the first direction X, denoted by Y.

(13) The bridge 19 is associated with a motor 24, equipped with an inverter 24, which enables it to move along the X axis of FIG. 1, while the motorized carriage 20 is associated to a relative motor (not shown for the sake of simplicity), also equipped with a respective inverter.

(14) As illustrated in greater detail in the following, a control device is associated to the bridge crane, which control device includes a control unit 40 for imparting control actions to the motors of the bridge crane, and commanding (for each motor) a respective inverter which regulates the velocity of the engine to which it is associated.

(15) In a variant of the invention, the control unit 40 can command via a PLC (Programmable Logic Controller) or another control unit, which in turn acts on the inverters of the motors.

(16) A pulley 11 is associated to the carriage 20, which pulley is in turn provided with a gripping element 12, for example a hook, and can raise or lower a load (not shown for the sake of simplicity) using a system of cables 27 operated by a hoist 18 mounted on the cross member 17.

(17) The gripping element of the load 12 can thus be raised or lowered along a vertical direction, but can also be subject to movements in which the load 12 deviates from the vertical, depending on working conditions, for example when the bridge 19 and/or the carriage 20 are in motion, or when a force is applied by an operator.

(18) In FIG. 2 the crane of FIG. 1 is represented in terms of its main components, so as to highlight an inertial platform 30 able tb measure the movements of the cable bearing the gripping element of the load, as illustrated in the following description.

(19) A device for the active control of stability according to the various embodiments of the present invention is also associated to the bridge crane 10.

(20) With reference to FIG. 3, note that the control device comprises the inertial platform 30 and the control unit 40, the control unit being able to impart motion commands to the inverters that control the activation of the bridge crane motors.

(21) The control unit 40 can then issue commands both to the inverter 24 which adjusts the motor 24 activating the movement of the bridge 19, and to the inverter regulating the motor that drives the movement of the carriage 20; these commands are mutually independent and can be sent to the inverters of the motors by means of an analog, canbus or other ethernet bus connections.

(22) In particular, the inertial platform 30 comprises a three-axis accelerometer 34 and a gyroscope 36, both being manageable by a microprocessor 32.

(23) In a preferred embodiment the control unit 40 can be mounted on the actual bridge crane (as indicated in the left part of FIG. 3) and be connected by cable 42, or in wireless mode, to the inertial platform 30.

(24) In another preferred embodiment the control unit 40 can be associated to the remote control unit, for example incorporated in a server 80, where the remote unit can operate control and system configuration software, as well as data post-processing software and can interface with a Cranes Integrated Management Services (CIMS) type platform as described in patent IT 1 393 950, which is incorporated herein for reference purposes.

(25) In a variant of the invention, the inertial platform 30 and the control unit 40 can be integrated in a single unit.

(26) With reference now to the inertial platform 30, the three-axis accelerometer 34 is capable of measuring the angle of inclination of the cable 27 which supports the gripping element of the load 12; however the angle measured only indicates the inclination of the cable relative to the vertical, but does not contain the information relative to the direction in which the cable is inclined.

(27) In order to complete the representation in space of the movements of the gripping member 12, the inertial platform 30 also includes a gyroscope 36.

(28) As known, the gyroscope 36 is an instrument that tends to maintain the axis of rotation thereof orientated in a fixed direction and thus enables measuring an angle of orientation with respect to the fixed direction.

(29) Therefore the combination of the information derived from the measurements made by the three-axis accelerometer 34 and the gyroscope 36 is used to determine the position of the gripping element 12 in the space, as expressed for example by the angle of FIG. 2, as well as to calculate the change over time of the angle as well as the angular acceleration .

(30) In a preferred embodiment of the invention, the inertial platform is placed on the fixed head of the cable supporting the gripping element.

(31) This arrangement of the inertial platform is preferable to a positioning of the inertial platform on the pulley 11, in that the pulley 11 is free Lo slide on the cables 27 and the gripping element has a tendency always to maintain a substantially vertical orientation. Therefore an accelerometer on the pulley would have the tendency of measuring accelerations considerably smaller than the accelerations measured when it is placed on the cable head.

(32) In any case, the data from the inertial platform 30 are sent to the control unit 40 to allow the control device to identify the corrections that must be provided to the carriage 20 and the bridge 19. These corrections are then activated by operating on the inverters of the respective drive motors in order to move the carriage 20 and/or the bridge 19 so as to bring the gripping element of the load into a vertical position, or to a desired angle, in a shorter time than that in which no control is present.

(33) The control device can also act in conjunction with the movement of the bridge and/or carriage to keep the angle of inclination of the cable within small values that allow for safe operation.

(34) In order to illustrate the functioning of the control system, reference is now made to FIG. 4, which is a schematic view of some relevant parameters for the system, illustrated according to an example that considers only the horizontal movement of one of the components of the crane.

(35) As the bridge crane can include a movement of the carriage 20 along a first axis and another movement, given by the bridge 19, along a second axis perpendicular to the first, all the concepts that follow can be applied on both axes.

(36) Since, however, the motions of these axes are decoupled from one another as they are generated by respective motors, operable independently of one another, for reasons of simplicity reference can be made to a casc of movement along ori axis alone, i.e. in the present example the X-axis shown in FIG. 4, with the movement along the second axis being schematized and controllable independently and in an entirely similar way.

(37) Therefore, one of the components of the bridge crane, which can be the carriage 20 or the bridge 19, is shown schematically as an example in FIG. 4, indicating the mass M and its position X, i.e. the distance of the centre of gravity of the mass M from a fixed reference. The mass M can move along the axis X.

(38) A weight m is constrained to the mass M by a cable or chain having a length 1. The weight m can therefore oscillate like a simple pendulum and can therefore deviate from the vertical by an angle .

(39) The weight m thus indicates the weight that the crane has to lift, where, depending on individual cases, the weight can be given by the weight of the gripping element supporting the load or the unloaded gripping element. The logic of the system remains the same in both cases.

(40) Therefore, to build a model of the dynamic performance of the system illustrated in FIG. 4, the following procedure can be employed.

(41) Firstly the Lagrangian function L of the system of FIG. 4 can be defined:
L=T?U

(42) where, as is known, T is the kinetic energy of the system and U the potential energy thereof.

(43) For the system illustrated in FIG. 4, using the generalized Lagrange coordinates, the following equations can be written:
T=?(M+m){dot over (x)}.sup.2+? ml.sup.2.sup.2+ml{dot over (x)} cos

(44) and
U=mgl(1?cos)

(45) where {dot over (x)} is the velocity along the axis X and is the angular velocity of the pendulum with length l and mass m.

(46) In this case it has been assumed that the cable has a constant length of 1 and a weight that can be considered irrelevant.

(47) With this premise the Euler-Lagrange equations for the system of FIG. 4 can be written, i.e:

(48) $\frac{d}{\mathrm{dt}}\frac{?L}{?\stackrel{.}{?}}-\frac{?L}{??}=-b\stackrel{.}{?}$$\frac{d}{\mathrm{dt}}\frac{?L}{?\stackrel{.}{x}}-\frac{?L}{?x}=F$

(49) where b is a parameter representing the frictions and F is a force applied to the system.

(50) Following the calculations, the following equations result:

(51) $\frac{d}{\mathrm{dt}}\frac{?L}{?\stackrel{.}{?}}-\frac{?L}{??}={\mathrm{ml}}^2\stackrel{\mathrm{.Math.}}{?}+\mathrm{ml}\stackrel{\mathrm{.Math.}}{x}\cos ?+\mathrm{mgl}\sin ?=-b\stackrel{.}{?}$$\frac{d}{\mathrm{dt}}\frac{?L}{?\stackrel{.}{x}}-\frac{?L}{?x}=\left(M+m\right)\stackrel{\mathrm{.Math.}}{x}+\mathrm{ml}\left(\stackrel{\mathrm{.Math.}}{?}\cos ?-{\stackrel{.}{?}}^2\sin ?\right)=F$

(52) Using the reference velocity {dot over (x)}.sub.ref of the motor displacing the mass M along the axis X of FIG. 4 as a control variable, and, with the hypothesis that the control of the velocity is rapid and accurate, the following can be posited: {umlaut over (x)}?{dot over (x)}.sub.ref.

(53) Defining the control action as u?{umlaut over (x)}.sub.ref and linearizing with the condition ==u=0, a dynamic model is obtained, defined by the equation (1), which represents the relation between the control action u and the dynamic parameters defining the position, the velocity and the acceleration of the mass m, i.e:

(54) $\begin{array}{cc}\stackrel{\mathrm{.Math.}}{?}\left(t\right)+\frac{b}{{\mathrm{ml}}^2}\stackrel{.}{?}\left(t\right)+\frac{g}{l}?\left(t\right)+\frac{1}{l}u\left(t\right)=0& \left(1\right)\end{array}$

(55) With reference to FIG. 5, the block diagram relating to an embodiment of the control system of the invention is described.

(56) In particular, in the hypothesis that the load gripping element is to be brought into the vertical position, i.e. attaining .sub.ref(t)=0, in the block diagram of FIG. 5 the controller C(s) (block 110) and the possible inputs of a bridge crane operator (block 100) are indicated.

(57) The controller C(s) receives as input the angular error .sub.e, given by the difference between the desired angle .sub.ref(t) and the angle measured by the inertial platform 30, i.e. .sub.m(t).

(58) The controller C(s), on the basis of the angular error .sub.s, calculates the reference or desired velocity v.sub.ref(t) to be set to the carriage aiming to reduce or eliminate the angular error .sub.s.

(59) The control system also includes the consideration of the eventual inputs of an operator of the bridge crane (block 100), if present.

(60) The reference or desired velocity v.sub.ref(t) translates into an effective velocity v(t) of the carriage by effect of the relative inverter-controlled motor, which effect includes the internal mechanisms of the motor and which is schematized by the transfer function M (s) of the block 120. In many cases, for the sake of simplicity, M (s)?1 can be posited.

(61) In turn the effective velocity v(t) of the carriage is used as an input for the dynamic model of the bridge crane (Eq. (1)) which supplies in output the effective angle (t) assumed by the cable bearing the load gripping element.

(62) This angle can be measured by the inertial platform 30 which returns a value .sub.m(t) to be used for calculating a new value of the angular error .sub.s.

(63) The controller C (s) can be proportional, i.e. C (s)=K.sub.p, where the gain K.sub.p links the angular error to the reference velocity v.sub.ref(t) for piloting the motors.

(64) The effective value of K.sub.p to be applied depends on the system. In general with high K.sub.p there is a rapid reduction in swing, though with a cost in terms of reduction of velocity of the carriage and vice versa.

(65) Further, to improve the performance of the system a further consideration must be the variation in length of the cable, account of which can be taken by a gain scheduled proportional controller, described in more detail in the following.

(66) Alternatively, the controller C (s) can be a PI controller, i.e. a proportional-integral controller.

(67) The functioning of the control system is entirely alike when an inclination is required of the gripping element of the load that is not the vertical, for example a degree during the movement of the whole bridge crane from one position to another on the work site. The only difference will be setting a different desired inclination, i.e. in the example .sub.ref(t)=1?.

(68) FIG. 6 illustrates a measuring example of the parameters describing the motion of the gripping element carried out using the inertial platform 30.

(69) In this case a first measurement can be taken by the accelerometer which measures, in the described case, the variation in acceleration of the load along axis Y. At the same time the gyroscope 36 can measure a variation in the attitude angle of the load along axis X.

(70) The measurements can be combined by means of known filtering methods, for example with the use of an extended Kalman filter, with the aim of obtaining a measurement of the variation of the angle along the axis Y with the algebraic sign thereof.

(71) To refine the performance of the control system, the gain K.sub.p of the controller can be considered to depend also on the distance 1 of the load from the carriage, as is schematically illustrated in FIG. 7.

(72) In this case a gain scheduled proportional controller can be used in operation.

(73) As is known, the gain scheduled control method implicates designing a controller for various functioning points of the system to be controlled. The parameters obtained in this way can then be interpolated in such a way as to design a controller which has a variable gain depending on the various functioning points.

(74) FIG. 7 illustrates, by way of example, a carriage 20 which displaces on the rails and a load of a mass m connected to the carriage by means of cables or chains which are considered to have an insignificant mass.

(75) The variables required for gain scheduling control are: the distance d between the hook of the head and the axis formed between the carriage and the load in stationary conditions (without oscillations), the angle of oscillation, estimated using the inertial platform, which is equal to the inclination angle of the cable that supports the load, and the range h.sub.max and h.sub.min within which the mass m can move along the vertical axis.

(76) FIG. 8 schematizes the functioning of the proportional controller. The angle of oscillation is obtained by the inertial platform and filtered with a high-pass filter so as to eliminate the continuous component, while the desired angle is zero, i.e. no oscillation at all. The difference error obtained is multiplied by a coefficient K.sub.p(h) depending on the height h of the load so as to obtain the correction of the velocity to be sent to the inverters which command the motors.

(77) Starting from the available data the height of the load is estimated (understood as being the distance from the carriage) with the objective of scheduling the control gain:

(78) $?=\frac{d}{\sin ?}$$h=\sqrt{{?}^2-d^2}$

(79) At this point h is estimated and is saturated between h_max and h_min, i.e. in such a way that h is always comprised between these values.

(80) From an initial system setting step, the two values K.sub.p to be applied at the maximum and minimum heights can be obtained, i.e. K.sub.p.sub._.sub.max and K.sub.p.sub._.sub.min. At this point, to calculate the value of K.sub.p the following formula can be used:

(81) $K_p\left(h\right)=K_{p\_\min }+\left(K_{p\_\max }-K_{p\_\min }\right)*\frac{h-h_{\min }}{h_{\max }-h_{\min }}$

(82) This solution enables opeiaLirig in all cases where the load is subject to significant excursions, passing from a lowered position to a raised position, for example by effect of the hoist 18.

(83) Lastly, in general, by locating the control unit in a remote position with respect to the lifting apparatus, apart from remote control operation, the apparatus can be integrated with a real-time data collection with the purpose of controlling the functioning of the lifting operation and the planning of its maintenance.

(84) The invention as it is conceived is susceptible to numerous modifications and variants, all falling within the scope of the inventive concept. Further, all the details can be replaced by other technically-equivalent elements.