FI88234C - DETAILED DESCRIPTION OF THE MEASURE - Google Patents

Abstract

The invention relates to a three-phase inverter bridge unit, containing for each phase a branch consisting of gate-controlled solid-state switches (T1'-T6'), said switches being used to convert a d.c. voltage into a three-phase a.c. voltage feeding a three-phase load (3'), and a control unit (5') for controlling the solid-state switches, and to a procedure for the use of the inverter bridge unit to prevent skewing of a lifting apparatus. The bridge unit comprises a parallel branch consisting of controlled solid-state switches (T7',T8') and connected in parallel with one of the branches of the bridge, said parallel branch being used along with the other phase branches feeding said three-phase load to feed another three-phase load (4'). <IMAGE>

Description

88234

REVERSE BRIDGE UNIT AND METHOD OF USING THEREOF -VÄXELRIKTARBRYGGENHET OCH FÖRFARANDE FÖR DESS ANVÄNDNING

The present invention relates to a reversing bridge unit according to the preamble of claim 1 and to a method for operating the same.

The skewing of cranes arises from the differences between the rotational speeds of the transmission motors, which are determined e.g. the load torques of the various motors, the motor-specific residue dependencies and the impedance differences of the supply lines.

Skidding can also be caused by differences in wear or friction of the crane's drive wheels, 15 dirt accumulated on the load-bearing surfaces, slipping during braking, etc.

Today, cranes use separate frequency converters to feed skew, which are fed by reversing bridges; each with its own transmission engine. The skew correction is performed in 20 known solutions according to Fig. 1 by using a control unit which performs the necessary measurements, a comparison of the results and the control functions required by each reversing bridge.

25 It is also possible to use a steel structure so rigid that there is no skew. This sometimes guides the mechanical design.

The known solutions have e.g. the following disadvantages:

Structures have to be oversized or special design used instead of a standard solution to achieve the rigidity required by the object.

35 Cranes may end up with a more complex mechanical structure than the basic function of the crane would require because --- τ— 2 88234 an economically advantageous and reliable method of preventing skidding is not used.

The increasing use of remote control (both in new cranes 5 and in modernization sites) also places additional demands on the prevention of crane skewing due to the lack or inadequacy of direct (local) driver control. The anti-skidding must then be fast and automatic.

10

Automation is most often based on agreed positioning accuracy, which can be a determining factor in the cost level of automation. In addition to preventing mechanical disadvantages due to skewing, these applications generally require a fairly precisely synchronized running between the ends of the crane in order to achieve a sufficiently good load positioning accuracy.

The object of the present invention is to obviate the drawbacks of the prior art. According to the invention, the rotational speeds of the motors (or motor groups) fed by the reversing bridges can be set or corrected independently by adding a parallel branch to the coupling component pair 25 supplying the phase of the reversing bridge according to the claims below. Thus, the three-phase system supplying each motor is similar for the two phases, but the voltage of the third phase can be adjusted separately.

The invention achieves the following advantages over the prior art: its reversing bridge solution with its controls is compact, its number of semiconductor components is smaller and its control is simpler than in the solutions according to the prior art.

35 3 88234

In the following, the invention will be described in more detail by way of example with reference to the accompanying drawings, in which

Figure 1 shows a solution according to the prior art implemented with separate 5 reversing bridges.

Figure 2 shows a solution according to the invention implemented with one reversing bridge.

Figure 3 shows the measurement of skew.

Figure 4 shows another skew measurement application.

Figure 1 shows a prior art arrangement with inverters 15 for correcting crane skew. It has two short-circuit motors 3 (M1) and 4 (M2), each using its own crane transfer mechanism. Both motors are supplied by an inverter generating symmetrical three-phase electricity, motor 3 (M1) is supplied by inverter 1 and motor 20 (M2) by inverter 2. Inverter 1 is controlled by control unit 9 and inverter 2 is controlled by control unit 10. DC circuits supplying inverters are not shown in Fig. 1, and nor the normal control of the inverters.

25 The position of each crane part used by the transmission is measured by the position measuring units 6 and 7. Their data are compared with each other in the comparison / correction unit 8, which sends a skew correction command to the control unit 9 and / or 10, which controls bridge transistors T1 to T6 and T7 to T12.

30

According to the prior art, the deviation caused by skewing can also be measured from only one part of the crane, in which case no comparison is required, and skewing can only be corrected by controlling another inverter.

35 4 88234

In the solution according to the invention shown in Fig. 2, one three-phase reversing bridge 1 1 is used to supply both motors 3 'and 4'. The bridge has transistors T1 'to T6' as above in bridge 1 of Fig. 1 for supplying the motor 3. In addition, a parallel branch formed by transistors T7 'and T8' is added to the power stage of the bridge in parallel with the pair of transistors T3 ', T6' supplying one phase. Thus, in two phases of the bridge, the same branch and thus the same transistors T1 ', T2', T4 'and T5' are connected to both motors.

In one step, the transistors T3 'and T6' of the first branch are connected to the first motor 3 'and the transistors T7' and T81 of the second branch parallel to the first branch to the second motor 4 '.

In Fig. 2, the position of the crane or a part thereof is measured by position measuring units 6 'and 7', the data of which are compared in a comparison / correction unit 8 ', which sends a skew correction instruction to the control unit 9'. which, according to the invention, controls the semiconductor switches of the bridge 1 '.

20

The difference from the prior art is that the number of semiconductor switches in the bridge 1 'is smaller than the total number of semiconductor switches in the bridges 1 and 2 according to the prior art of Fig. 1. A further difference is that the control unit 9 'of the bridge according to the invention is now one unit, while the prior art skew correction of Fig. 1 has two control units 9 and 10.

. ; The control of the bridge 1 'can take place by a separate control, for example an asymmetrical stator voltage limitation is applied to the motor to be controlled by reducing the voltage of one phase, whereby the rotational speed can be set independently, even if the fundamental frequency remains the same. Rotation speed setting: in this case based on the to reduce the peak torque of the motor by 35 and to taper the torque curve.

5,882,334

Figure 3 shows the measurement of crane skew. The structure of the crane is formed by a substantially rigid main support 11 and ends 12a and 12b rigidly attached to it. The crane moves on guide rails 13a and 13b, which are substantially parallel. The crane is described as sloping, ie the entire crane is slightly rotated horizontally relative to the rails. The crane lifting gear is not described.

The oblique travel of the crane is detected by measuring the position of the end 12a or 12b 10 relative to the guide rail 13a or 13b or other fixed structure using proximity sensors or proximity switches 14.

The skew correction can take place as described in the description 15 of Fig. 2, for example by limiting the voltage of the transfer motor (s) at the upstream end of the crane until the situation is corrected, i.e. the ends 12a, 12b are parallel to the rails 13a, 13b.

Figure 4 shows another measurement of crane skew. The crane • cannot now rotate horizontally as shown in figure 3.

The direction of the end 15a or 15b remains substantially parallel to the guide rail 13a *: or 13b, but the structure of the crane itself now appears skewed due to changes in position or deflections.

The second end 15a or 15b or both ends 15a and 15b may be articulated to the main support 16, and the position difference 30 between the main support 16 and the ends 15a and 15b is measured by displacement sensors 17a and 17b mounted between the ends and the main support. Of course, the position difference can also be measured with a rotation sensor mounted on the joint between the main support and the end.

The skew can also cause a stress state in the crane structures, which can be detected by β 38234 steel structure stress level sensors 18, which sensors can be attached to the main support 16 or, for example, to end supports or a separate measuring rod placed 5. in a position corresponding to the above-mentioned displacement sensors 17a and 17b.

The skew correction of Fig. 4 takes place in the same way as in Fig. 3.

The cranes of Fig. 3 or Fig. 4 can be of various constructions, for example semi-gantry or gantry cranes, the end (s) of which can be, for example, so-called A-pukkiraken-dimensional.

It will be apparent to those skilled in the art that the various embodiments of the invention are not limited to the examples set forth above, but may vary within the scope of the claims set forth below.

Claims (8)

1. A three-phase reversing bridge unit with gate-controlled semiconductor switches (T1 '~ Reversing bridge unit according to Claim 1, characterized in that the loads are asynchronous motors and in that the control unit controls the rotational speeds of the motors connected to the parallel branches. 20 independently. Reversing bridge unit according to Claim 1 or 2, characterized in that the control unit sets the rotational speed by an asymmetrical stator voltage limitation 25, in which the phase voltage of the parallel branch is reduced. Reversing bridge unit according to Claim 1 or 2, characterized in that the control unit adjusts the rotational speed by means of single-phase braking, in which a similar voltage is applied to the two phases of the motor to be set. A method of using a reversing bridge unit 35 according to claim 1 to prevent skewing of a hoisting device, the method using a three-phase reversing β 88234 orientation bridge unit having gate-controlled semiconductor switches (T11 to T6 ') with branches of each phase of the bridge a voltage for three-phase, an AC voltage supplying a three-phase asynchronous motor (3) or motor group for the first transmission-5 mechanism of the hoisting device, and a control unit (5) for controlling semiconductor switches, measuring the position of the hoist or part thereof with position measuring units (6 ', 7'); characterized in that at least one parallel branch consisting of controllable semiconductor switches (T71-T8 ') in parallel with one branch of the bridge is used in the reversing-10 rear bridge, which together with the other phases of the second asynchronous motor (3) n branches to supply a second three-phase asynchronous motor (4) or motor group to be used as the hoist transfer device of the hoist, and that the motor speeds of the hoist or its parts are set 20 sex. 5 T6 ') are formed by the branches of each phase of the bridge, by which the semiconductor switches alternately direct DC voltage into three-phase AC supplying three-phase load (3), and a control unit (5') for controlling semiconductor switches, characterized in that the bridge unit always has at least 10 controllable semiconductors. T7 ', T8'), a parallel branch connected in parallel with one branch of the bridge, which together with the branches of the second stages supplying said three-phase load supplies a second three-phase load (4). 15 Method according to Claim 5, characterized in that the skew of the hoisting device is detected by measuring the position of the hoisting device between it and the fixed structure by means of position measuring sensors (6 ', 7 *). Method according to Claim 5, characterized in that the skew of the hoisting device is detected by displacement sensors (17a, 17b) which measure the change in position between two mutually moving parts of the hoisting device, such as the main crane support and the crane end. 7 88234 Method according to Claim 5, characterized in that the skew of the hoisting device is detected by sensors (18), 9 88234 measuring the stress level of the steel structure of the hoisting device, which sensors are arranged directly on the steel structure of the hoisting device or on a measuring rod attached to the steel structure. 10 88234