GB2030727A

GB2030727A - Bridge crane control

Info

Publication number: GB2030727A
Application number: GB7927529A
Authority: GB
Original assignee: Heemaf BV; Heemaf NV
Current assignee: Heemaf BV; Heemaf NV
Priority date: 1978-09-25
Filing date: 1979-08-07
Publication date: 1980-04-10
Also published as: GB2030727B; NL7809720A; FR2436745A1; DE2930564A1

Abstract

The movement of the crab and the length of the tackle of a bridge crane is controlled. The initial position and the desired terminal position of the crab and the tackle and the maximum permissible tackle lengths during transport for different acceleration values are used with the pulse moment law: <IMAGE> wherein phi =angle of displacement with respect to the vertical, y=length of the tackle and g=gravitational acceleration and x=crab position. The equation is simulated using analog circuitry S. The residual swing of the tackle at the terminal position is repeatedly calculated, the acceleration is assessed by comparing the results at which the residual swing is at a minimum in unit 6 and the measured acceleration value is applied via integrator 9 to the drive of the bridge crane. <IMAGE>

Description

SPECIFICATION Bridge crane control The invention relates to a method and a device for controlling the movement of the crab and the length of the tackle of a bridge crane.

In prior art systems the angle of displacement of the tackle is measured and the movement of the crab is varied accordingly to an extend such that at the terminal position the angle of displacement of the tackle is zero or substantially zero.

It is furthermore possible to fix empirically given patterns of movement as a function of the path to be covered and to carry them automatically into effect.

The disadvantage of the first-mentioned control-method resides in that it is difficult to measure the angle of displacement, whilst in addition the control-system is complicated. The second method has the disadvantage that the performance of the movement is not optimal, since a selection has to be made among a number of existing patterns.

The invention has for its object to provide a control-method in which a load can be conveyed with the aid of a bridge crane to the desired place of destination within the shortest possible time and with a minimized residual swing of the tackle.

According to the invention this is achieved in that on the basis of the starting position and the desired terminal position of the crab and the tackle and of the tackle lengths maximum permissible during the transport for different acceleration values and by using the pulse moment law: d2? 2 dy dy g cos.cp = d2x + . ~~~ . ±sin.y= + dt2 y dt dt y y dt2 wherein ç = angle of displacement with respect to the vertical, y = length of the tackle, g = gravitational acceleration and x = crab position, the residual swing of the tackle in the terminal position is repeatedly calculated, in that the acceleration is assessed by comparing the results in which the residual swing is a minimum and in that the measured acceleration value is fed to the control-mechanism of the bridge crane.

In the proposed method, prior to the control of the bridge crane, the desired pattern of movement can be optimized, it being supposed that the calculations can be rapidly carried out, so that waiting time will be negligible. The control-system according to the invention constitutes an open i.e. non-feedback control. Prior to the calculations a number of acceleration values can be excluded on account of the tackle lengths maximum permissible during transport and of the distance to be covered by the crab. This provides the advantage that only a limited number of calculations has to be made, since those acceleration values which are not relevant are excluded in advance.This can be achieved in that the acceleration values to be used are divided into two groups, one of which is used with maximum permissible tackle lengths and a distance to be covered by the crab below selected values and the other with maximum permissible tackle lengths and a distance to be covered by the crab above selected values.

Obviously, in order to carry out a large number of calculations within the shortest possible time it is preferred to use electronic means. For this purpose the invention proposes a device for carrying out said method, which is characterized by an analogue simulator circuit for simulating the differential equation:: d2? 2 dy dy g cos.ç= d2x -+ + ---- . +sin.q = dt2 y dt dt y y dt2 by a generator circuit for generating different pulse signals and for applying them to the simulator circuit, by a comparison circuit connected to the output of the simulator circuit for repeatedly comparing the output signals thereof to preceding output signals and for assessing the output signals with the lowest possible y(t), by a memory connected to the comparator and the generator for storing the pulse signal associated with the g7(t), and by a circuit connected to the memory for generating control-signals for the bridge crane.It is furthermore proposed to use an excluding circuit connected to the simulator circuit and to the generator circuit for excluding undesired pulse signals formed by the generator circuit on account of the maximum permissible tackle lengths during transport. Since the resultant signals are analogue signals, the control-signals are fed to the bridge crane through an integrator circuit.

The invention will be explained with reference to a block diagram shown in the accompanying drawing.

In the block diagram x0 is the starting position of the crab, y0 the initial length of the tackle, Yd the desired final length of the tackle, xd the terminal position of the crab, y0 the initial speed of the tackle movement, Kh, Kl, Kr are the limit values of the region not to be occupied by the tackle, a(t) is the acceleration value, y(t) the instantaneous tackle length and q9(t) the angle of displacement with respect to the vertical.

The initial conditions are stored in the memory 2. These are the data xO, yg, y0, L,. Kh, K,, Kr Then a starting order Sl is given to actuate the control-circuit 1. As a result said initial conditions are stored in the memory 2. On the basis of the initial data the selection switch 10 decides whether the so-called short or long programme has to be carried out. The selection is made on the basis of the path to be covered by the crab and of the variation of the tackle length to be expected. When the short programme is chosen, only those acceleration values are generated which are appropriate to a short-time transport The result of the selection is transferred by the circuit 10 by means of a signal S2 to the control-circuit 1.

By means of the signal S3 the control-circuit 1 governs the generator 3, which forms in order of succession a plurality of acceleration values a(t). It should be noted that only useful values to a(t) are generated. Acceleration values which the drive cannot realize are not produced. Each acceleration signal is fed to the circuit 4, which has furthermore received the signals Kh, K,, K, from the circuit 2. On the basis of these data the circuit 4 forms the signals y(t) andy(t), which represents the hoisting speed of the tackle as a function of time. Said signals are fed to the simulator circuit 5, which is an electronic model of the tackle and in which in known manner by means of operation amplifiers, choice of resistors.

inductors and capacitors the differential equation: d2? 2 dy dy g cos.G) = d2x - + ----- . . +sin.? = dt2 y dt dt y y dt2 is simulated. As a result the circuit 5 provides the angle of displacement v(t) and the angular speed (p(t).

The latter signals are fed to the comparison circuit 6. This circuit 6 compares the applied values to the previously produced value, selects therefrom the value so far most desirable and applies these signals to the memory 7. It should be noted that the most desirable value is that value at which the calculated residual value of the swing is a minimum. The associated value of the acceleration is stored out of the generator 3 in the memory 7. After the optimum value is thus obtained, the driving generator circuit 8 is actuated by means of the signal S4, said circuit receiving the optimum value from the memory 7 and applying the generated control-signal to the integrator 9. The drive of the bridge crane is controlled from the integrator 9.

Claims

1. A method of controlling the movement of the crab and the length of the tackle of a bridge crane characterized in that on the basis of the initial position and the desired terminal position of the crab and the tackle and of the maximum permissible tackle lengths during transport for different acceleration values, by using the pulse moment law:: d2? 2 dy dy g cos.go = d2x + + ---- ---- ---- . --±sin.y= dt2 y dt dt y y dt2 wherein ç = angle of displacement with respect to the vertical, y = length of the tackle and g = gravitational acceleration and x = crab position, the residual swing of the tackle at the terminal position is repeatedly calculated, said acceleration is assessed by comparing the results at which the residual swing is at a minimum and the measured acceleration value is applied to the controlmechanism of the bridge crane.

2. A method as claimed in Claim 1 characterized in that the acceleration values are selected on the basis of the maximum permissible tackle lengths during transport and of the distance to be covered by the crab.

3. A method as claimed in Claim 2 characterized in that the acceleration values to be used are divided into two groups, one of which is used with maximum permissible tackle lengths and the distance to be covered by the crab below selected values and the other with maximum permissible tackle lengths and the distance to be covered by the crab above selected values.

4. A device for carrying out the method claimed in Claims 1 to 3 characterized by an analogue simulator circuit for simulating the differential equation: d2? 2 dy dy g COS.ev= d2x + . -- . ---- dt2 y dt dt y y dt2 by a generator circuit for generating different pulse signals and for applying them to the simulator circuit, by a comparison circuit connected to the output of the simulator circuit for repeatedly comparing the output signals thereof to preceding output signals and for assessing the output signals with the lowest possible (p(t), by a memory connected to the comparator and the generator for storing the pulse signal associated with the Ç)(t) and by a circuit connected to the memory for generating control-signals for the bridge crane.

5. A device as claimed in Claim 4 characterized by an excluding circuit connected to the simulator circuit and to the geneator circuit for excluding undesired pulse signals formed by the generator circuit on the basis of the maximum permissible tackle lengths during transport.

6. A device as claimed in Claims 4 and 5 characterized in that the control-signals are applied to the bridge crane through an integrator circuit.

7. A method and device of controlling the movement of the crab and the length of the tackle of a bridge crane substantially as hereinbefore described with reference to the accompanying drawing.