Automatic leveling control method for a four-leg support working platform

An automatic leveling control method for a four-leg support working platform, with the four-leg support working platform comprising 4 legs, an upper end of each leg being connected with a lower horizontal surface of the four-leg support working platform, a lower end of each leg being supported on ground, each leg having an identical structure and an identical maximum actuating stroke and being identically connected to the four-leg support working platform at a respective connection point, a force sensor for measuring vertical load being installed between each leg and the four-leg support working platform, wherein the method comprises the following steps:

• step 1, driving one of the 4 legs to contract to be detached completely off the ground, treating a vertical load residual on the leg as a measurement error and clearing the measurement error to zero in calculation, then driving the leg to extend to support on the ground, performing identical operations successively for the other three legs;
• driving the four legs to fully support the four-leg support working platform, and adjusting each leg to bear the vertical load, recording the vertical load as Fi, with i ranging from 1-4;
• establishing a coordinate system by taking a symmetry center of the connection points between each leg respectively and the four-leg support working platform as a coordinate origin and longitudinal, transverse and vertical directions of the four-leg support working platform as an x, a y and a z axis respectively;
• denoting a coordinate of each connection point as (xi, yi, zi), denoting a total weight of the four-leg support working platform as G;
• obtaining, in accordance with a torque balance relationship of the four-leg support working platform along the x, along the y axes and a force balance relationship along the z axis respectively, and with positive directions of torques and inclination angles being determined in accordance with right hand screw rule, a longitudinal and a transverse coordinate of a mass center of the four-leg support working platform and the total weight of the four-leg support working platform respectively as:
• {
• x
• G
• =
• 1
• G
• ⁢
• ∑
• i
• =
• 1
• 4
• F
• i
• ⁢
• x
• i
• y
• G
• =
• 1
• G
• ⁢
• ∑
• i
• =
• 1
• 4
• F
• i
• ⁢
• y
• G
• =
• ∑
• i
• =
• 1
• 4
• F
• i
• ;
• (
• 1
• )
• step 2, dividing the four-leg support working platform into 4 virtual rectangular blocks along the longitudinal and transverse directions and from the origin of the coordinate system, corresponding to four quadrants of an xy plane of the coordinate system described in step 1, defining the virtual rectangular block where the coordinates of the mass center is located as a main bearing quadrant;
• the main bearing quadrant being a first quadrant if the x and y coordinates of the mass center are both positive values;
• the main bearing quadrant being a second quadrant if the x and y coordinates of the mass center are negative and positive values respectively;
• the main bearing quadrant being a third quadrant if the x and y coordinates of the mass center are both negative values;
• the main bearing quadrant being a fourth quadrant if the x and y coordinates of the mass center are positive and negative values respectively;
• selecting any three legs from the 4 legs and forming a virtual triangular block from the corresponding three connection points;
• forming other three virtual triangular blocks from remaining selection of three legs from the 4 legs;
• selecting the virtual triangular block that fully covers the main bearing quadrant as a main bearing zone, and designating the three corresponding legs forming the corresponding virtual triangular block as active legs, and designating a remaining leg as a driven leg;
• step 3, driving the driven leg to extend a specified vertical displacement, then contract to an original length thereof, while keeping the legs other than the driven leg unactuated;
• measuring changes of the inclination angle of the four-leg support working platform around the x and the y axes corresponding to extension of the driven leg to the specified vertical displacement;
• obtaining a vertical displacement actuation length of the driven leg under a unit inclination angle change by means of dividing the specified vertical displacement with a larger absolute quantity of the changes of the inclination angle of the four-leg support working platform around the x or they axes;
• step 4, controlling a contracting actuation of the driven leg until the vertical load thereof diminishes to zero, this state when a leg bearing a zero vertical load is defined as a weak leg state;
• step 5, setting an inclination angle threshold εθ of the four-leg support working platform, measuring the inclination angles of the four-leg support working platform around the x and the y axes respectively, calculating absolute values of the two inclination angles respectively;
• proceeding to step 8 on condition that the absolute values of the two inclination angles are both smaller than the inclination angle threshold εθ;
• otherwise proceeding to step 6;
• step 6, calculating an target actuation length for the leveling control for said each leg according to an expression βx1−αy1, βx2−αy2, βx3−αy3, βx4−αy4, wherein α and β are the inclination angles of the four-leg support working platform around the x and y axes respectively in a current state;
• determining a proportional relationship of the target actuation lengths of the four legs, setting an actuation speed of said each leg according to the proportional relationship;
• step 7, measuring the implemented actuation length of each active legs;
• proceeding to step 8 if the implemented actuation length of the each active leg is greater than or equal to the respective target actuation length of said each active leg;
• controlling said each leg to actuate simultaneously and in accordance with the actuation speed;
• contracting the driven leg to the weak leg state if a measurable vertical load of the driven leg is detected by the force sensor;
• proceeding to step 7;
• step 8, measuring the inclination angles of the four-leg support working platform around the x and y axes respectively, calculating the absolute values of the two inclination angles respectively;
• proceeding to step 9 on condition that the absolute values of the two inclination angles are both smaller than the inclination angle threshold εθ;
• otherwise proceeding to step 6;
• step 9, setting a limit inclination angle threshold εγ of the four-leg support working platform, wherein the limit inclination angle threshold εγ is larger than the inclination angle threshold εθ;
• calculating a difference εγ−εθ between the limit inclination angle threshold with the inclination angle threshold, multiplying the difference by the vertical displacement actuation length of the driven leg under the unit inclination angle change described in step 3 to obtain a limit compensating actuation length εz of the driven leg;
• step 10, controlling a compensating actuation of the driven leg, and measuring a compensating actuation length of the driven leg, while simultaneously measuring the inclination angles of the four-leg support working platform around the x and y axes;
• continually performing the compensating actuation of the driven leg on condition that the compensating actuation length is smaller than the limit compensating actuation length εz, and the absolute values of the inclination angles of the four-leg support working platform around the x and y axes are both smaller than the limit inclination angle threshold εγ;
• otherwise locking all four legs and concluding automatic leveling control method.