Self-balanced apparatus for hoisting and positioning loads, with six degrees of freedom

Abstract

An apparatus for hoisting and positioning a load in a self-balanced manner regardless of the position of its center of gravity. The apparatus comprises an upper platform adapted for being hoisted from a general hoisting point, a lower platform adapted the attachment of a load to be hoisted and positioned, and a six degrees of freedom actuator comprising six variable length tendons, adapted for moving the lower frame with respect the upper frame in the three directions of the space and tilted around the three axis of the space. A configurable counterweight system supported by the upper platform is arranged for modifying the center of mass of the apparatus over a horizontal plane, and processing means are configured for dynamically calculating a desired position of the counterweight system, for balancing the apparatus with the respect to a general hoisting point.

Claims

1. An apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom, comprising: an upper platform adapted to hang from a general hoisting point; a lower platform arranged below the upper platform and adapted to hold the load to be hoisted and positioned; a six degrees of freedom actuator having six variable length tendons connected with the upper platform and with the lower platform, such that the lower platform is suspended from the upper platform through the six variable length tendons; wherein the six degrees of freedom actuator is adapted for moving a lower frame with respect to a upper frame in three directions of space and tilted around the three axis of the space; at least one configurable counterweight system supported by the upper platform, arranged for modifying a center of mass of the apparatus over a horizontal plane allowing a minimum of two degrees of freedom; a load measuring means adapted for individually measuring forces transmitted by each one of the six variable length tendons; a processing means configured for dynamically calculating a desired position of the counterweight system, based on weight and center of gravity measures provided by the load measuring means, for balancing the apparatus with the respect the central hoisting point, and a counterweight system control means for moving the counterweight system to the desired positions calculated by the processing means.

2. The apparatus of claim 1, wherein the upper platform has three vertexes spaced within a first plane, and wherein the lower platform has three vertexes spaced within a second plane, and wherein each of the variable length tendons is coupled in an articulated manner with one vertex of the lower platform and with one vertex of the upper platform.

3. The apparatus of claim 1, wherein the lower frame is suspended from the upper frame by means of the variable length tendons, such that the variable length tendons are tensioned by the weight of the lower platform and any load attached to the lower platform.

4. The apparatus of claim 3 further comprising: a winch mechanism for each variable length tendon for varying the length of the same, and wherein each variable length tendon has one end articulately connected with one vertex of the lower platform, and another end is connected to the associated winch mechanism such that the length of each variable length tendon is varied by alternatively rolling and unrolling each tendon on the associated mechanism.

5. The apparatus of claim 4, wherein the winch mechanisms are coupled with the upper triangular frame, and each vertex of the upper triangular frame has two free-spinning pulleys, and an intermediate part of each tendon is placed to roll on the tendons associated pulley as the tendon is being extended and retracted by the respective winch mechanism.

6. The apparatus of claim 3, wherein each variable length tendon is one of a cable, a link chain, and a strap-like element.

7. The apparatus of claim 1, wherein the load measuring means are adapted for individual measuring axial tension in each variable length tendon.

8. The apparatus of claim 1, wherein the counterweight system includes at least one mobile counterweight displaced within at least one plane.

9. The apparatus of claim 8, wherein counterweight system includes three counterweight devices placed above one another, such that the weights of the counterweight devices are displaceable on parallel and overlapping planes.

10. The apparatus of claim 9, wherein the counterweight devices are arranged such that each weight is displaceable along a straight line passing through any axis of the upper platform.

11. The apparatus of claim 1, wherein at least one of the upper platform and the lower platform have a triangular frame and are arranged such that the relative position of the triangular frame is offset with respect to each other.

12. The apparatus of claim 1, wherein at least one of the upper platform and the lower platform have an equilateral triangular frame.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Preferred aspects of the present disclosure are henceforth described with reference to the accompanying Figures, wherein:

(2) FIG. 1A shows a perspective view of an example of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(3) FIG. 1B shows an elevational front view of an example of an upper platform of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(4) FIG. 2A shows a perspective view of another example of the upper platform of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(5) FIG. 2B shows a bottom plan view of an example of an upper platform of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(6) FIG. 3 shows a perspective view of an example of a counterweight device of a counterweight system of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(7) FIGS. 4A and 4B show schematic representations in plant view of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure, which serves to illustrate the operation of the counterweight system of the present disclosure. The position of each variable length tendon is represented with broken lines in FIG. 4A.

(8) FIG. 5 shows a perspective view of one of a motor-driven winding spool for varying the length of the tendons of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(9) FIG. 6A shows a front elevational view of a proposed means for measuring the axial tension in each tendon of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(10) FIG. 6B shows a cross-sectional view taken along line A-A of a proposed means for measuring the axial tension in each tendon of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure,

(11) FIG. 6C shows a cross-sectional view taken along line B-B of a proposed means for measuring the axial tension in each tendon of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure, and

(12) FIG. 6D shows a schematic representation of an example of an operating principle of a measuring device of a proposed means for measuring the axial tension in each tendon of an apparatus for hoisting and positioning a load in a self-balanced manner with six degrees of freedom in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

(13) FIGS. 1A and 1B show an exemplary aspect of the apparatus of the present disclosure, which comprises an upper platform (1) and a lower platform (2) arranged below the upper platform, and a six degrees of freedom actuator (3) connected with the upper and lower platforms (1,2), as to configure an inverted Stewart platform for moving the lower platform (2) relative to the upper platform (1), such as a part (not shown) attached to the lower platform (2) can be moved with six degrees of freedom at the same time that it is being hoisted. The apparatus is intended to provide a way of easily achieving accurate movements of the load, while coarse displacements can be obtained via an overhead crane or any other industrial apparatus for material handling.

(14) The upper platform (1) includes an upper equilateral triangular frame (6) adapted for being hoisted from a general hoisting point; for that purpose, the apparatus includes a connection member (4) having a ring or eye (8) (which defines said general hoisting point), for receiving the hook of a crane (not shown), and three rods (9a, 9b, 9c) with same length and having opposite ends connected respectively with the connection member (4) and with the upper platform (1). The points at the upper frame where the three rods (9a, 9b, 9c) are connected, are spaced in such a way so that the ring or eye (8) is vertically aligned with the geometric center of the upper triangular frame (6).

(15) On the other hand, the lower platform (2) includes a lower equilateral triangular frame (7) adapted for the attachment of a part to be lifted and positioned.

(16) The six degrees of freedom actuator (3) comprises six variable length tendons (5a, 5b, 5c, 5d, 5e, 5f), which in this aspect consist of a cable or strap of suitable material. Each of the three vertexes of the upper and lower triangular frames (6,7), is provided with articulated connection means, such as each tendon (5a, 5b, 5c, 5d, 5e, 5f), is connected between one the three vertexes of lower triangular frame (7) and one of the three vertexes of upper triangular frame (6), such as, the lower triangular frame (7) is suspended from the upper triangular frame (6), and the tendons are tensioned by the weight of the lower frame and any load attached to it.

(17) Preferably, upper and lower triangular frames (6,7) have the same size, and are offset to each other as shown more clearly in FIG. 4A. In this way, the working space, that is the space wherein the center of gravity of the assembly formed by the lower platform and a piece attached to it, can be moved without compressing the six variable length tendons, is axis-symmetric. As shown more clearly in FIG. 4A, in a plan view, the working space is a regular hexagon obtained by the intersection of the two upper and lower triangular frames.

(18) For varying the length of each tendon, a winch mechanism (10a, 10b, 10c, 10d, 10e, 10f) such as the motor-driven winding drum shown in FIG. 5, is individually provided for each one of the six tendons (5a, 5b, 5c, 5d, 5e, 5f), and as shown in FIG. 1A, each variable length tendon has one end articulately connected with one vertex of the lower triangular platform (7), and another end connected with its associated winch mechanism, such as the length of each variable length tendon is varied by alternatively winding and unwinding each tendons on its associated winch mechanism.

(19) Each winch mechanism (10a, 10b, 10c, 10d, 10e, 10f), conventionally comprises a pulley (12a, 12b, 12c, 12d, 12e, 12f) driven by an electric motor (17) through a reduction gearbox. The winch mechanism includes a brake, built-in encoder, and it is controlled by a closed-loop electronic frequency inverter.

(20) In the aspect of FIG. 1A, the winch mechanisms (10a, 10b, 10c, 10d, 10e, 10f) are coupled with the upper triangular frame (6). In this aspect, each of the three sides of the upper triangular frame (6) has two winch mechanisms, and the pulleys of the same are placed approximately in the middle of that side. Each vertex of the upper triangular frame (6) has two free-spinning pulleys (11a, 11b, 11c, 11d, 11e, 11f), one for each of the two tendons connected to each vertex. An intermediate part of each tendon roll on its associated pulley as the tendon is being extended and retracted by the respective winch.

(21) By controlling the operation of each winch mechanism (10a, 10b, 10c, 10d, 10e, 10f), the length of each tendon is individually varied, such as the lower triangle frame (7) can be moved with six degrees of freedom in all directions and angles of the space.

(22) A configurable counterweight system (13) is fitted to the upper triangular frame, and comprises at least one counterweight device (14) as the one shown in more detail in FIG. 3, which includes a lineal guide (15) and a weight (16) mounted on the lineal guide (15) and an electric motor (17), for moving the counterweight system to the desired positions calculated by the processing means, for linearly displacing the weight (16) along the guide (15), for example a ball screw drive, a chain, a belt or any other conventional technique. The counterweight device (14) is arranged such as its weight (16) is displaceable on a third plane parallel to the first plane. Control means for operating the counterweight system, may comprise a speed controller for the electric motors, encoders and electronic control means.

(23) Although any counterweight system able to displace a mass over a horizontal plane would be useful for the purpose of the apparatus, only the triple radial system hereby described allows obtaining the desired mass displacement in a progressive way, with minimum load jerks, and in a minimum time.

(24) Preferably, the counterweight system (13) comprises three counterweight devices (14a,14b,14c) placed one above the other, such as the weights (16a, 16b, 16c) of the counterweight devices are displaceable on overlapping planes, parallel to each other and parallel to the plane defined by the upper triangular frame (6). Additionally the relative arrangement of the three counterweight devices (14a, 14b, 14c) is shown in FIG. 4A, wherein it can be seen that each lineal guide (15a, 15b, 15c) of the counterweight devices (14a, 14b, 14c), is aligned with one bisecting line (bisector) of the upper or lower triangular frames (6,7), and pass through the central point of each counterweight devices (14a, 14b, 14c) is vertically aligned with the geometric center of the upper triangular frame (6).

(25) Load measuring means are provided for measuring axial forces transmitted by each of the six variable length tendons, which represent the degrees of freedom of the actuator device, in particular a load sensor (18a, 18b, 18c, 18d, 18e, 18f) is provided for each tendon (5a, 5b, 5c, 5d, 5e, 5f).

(26) The configuration of these load sensors (18) is represent in FIG. 6A, which is based on a set of three pulleys, two side pulleys (19,19) and a central pulley (20) assembled between front and rear walls (21,21), such as the respective tendon (5) under tension run through these three pulleys, and it is pressed against the central pulley (20) in its radial direction, so as to exert a resulting force proportional to the tension in the tendon (5).

(27) For measuring that force, the central pulley (20) has a load pin or load bolt (22) axially arranged therein. A load pin is known device conventionally used to measure radial forces applied to the axis of the load pin, formed by a rod-shaped metallic member having strain gauges for measuring deformation of that member.

(28) FIG. 6D shows the operating principle of this assembly, and the composition of forces in the axle (x) of the central pulley (20), where the angle (a) formed by the strands of the tendon (5) on the central pulley (20) is 120, showing that the resulting force (R) is equal to the tension of the tendon (5). If the angle () is not 120 the resulting force (R) is different to the tension of the tendon (T), but the forces relationship, could be easily calculated.

(29) The apparatus also includes processing means (not shown) such as an industrial computer, configured for dynamically calculating a desired position of the configurable counterweight system, based on weight and center of gravity measures provided by the load measuring means, and angle measures of the upper frame related to the horizontal plane.

(30) The self-balancing function of the apparatus is carried out by a control system including several encoders, level and load sensors, an industrial computer to solve the problem kinematic and dynamic of the Stewart platform and for implementing a control algorithm specifically developed for the apparatus, and a control post allowing a human operator to receive signals from and to send orders to the control system.

(31) The apparatus is capable of keeping itself balanced all time regardless of the position of the center of gravity of a load being hoisted by automatically setting a configuration, that is, a position of the weights of the counterweight system, such as the location of the center of gravity of the whole assembly is made coincident with the general hoisting point. At the same time, a part attached to the lower triangular frame (7), while it is being hoisted can be moved to any desired position by actuating the inverted Steward platform, obviously within the geometrical and physical limitations of the apparatus, and the mass compensation capacity of the counterweight system.

(32) As a part of the control system, a mathematical logical algorithm has been developed to determine the optimal position of the masses belonging to the counterweight system, for a given location of the center of mass and minimizing the distances to the center of the triangle.

(33) Taking into account a star or radial configuration for the counterweight system, as shown in FIGS. 4A and 4B the algorithm has the purpose of determining the position of the three weights (16a, 16b, 16c). This problem is mathematically indeterminate given that three variables must be defined for positioning the three weights, but only two equilibrium equations (X-axis and Y-axis) are available. The solution is attained by adding to the two equations a third condition, by imposing the counterweight displacement to be kept to a minimum.

(34) The mathematical procedures normally used to solve such systems of equations containing several inequalities are based on linear programming techniques or general numerical methods. In this particular case, given that only three unknown variables and one objective function are present, it is possible to solve for two variables by using the equilibrium equation, and then replacing their values in the objective function.

(35) By deriving the objective function respect to third variable and making it equal to zero, a relative maximum or minimum may be detected within the interval considered.

(36) In order to minimize the displacements of the counterweight system, several objective functions may be implemented. The best results have been achieved by adding the squares of the displacement of all masses, as taken from the geometrical center of the upper frame.

(37) Other preferred aspects of the present disclosure are described in the appended dependent claims.