DE1087335B - Lowering brake circuit for hoist drives - Google Patents

Description

The invention relates to a lowering brake circuit for hoist drives with three-phase asynchronous motors, which are DC excited for braking with disconnection from the mains and / or with an electrical controllable braking machine are provided, the characteristics of which have a stable and an unstable range having.

With hoists, there is a requirement to lower heavy loads slowly. With three-phase asynchronous motors, in which the stator is disconnected from the three-phase network for the slow lowering of the load and is fed with single-phase direct current at the same time and / or an electrically controllable braking machine is excited, there is a risk that when switching back from full lowering speed in the unstable area of the braking curve of the DC-excited asynchronous motor or the braking machine and the load can fall.

Using the torque-speed characteristic shown in FIG. 1 the behavior of the drive during lowering braking is to be explained.

A slip ring rotor is provided as the drive motor for hoists, which is the usual Way for the lifting and lowering operation with power is connected to the three-phase network and to achieve is excited by low lowering speeds with direct current.

In quadrant I, the load lifting is shown, in quadrant III the load lowering by motor and in quadrant IV the load lowering by generator (with pulling loads) in several starting stages. In quadrant IV, two characteristic braking curves br I and br 2 for a DC-excited asynchronous motor with constant excitation, but different rotor resistances, are also entered.

If you now switch back quickly from full lowering speed, switching to the DC braking at high speed does not apply the required braking torque, and the Load accelerates instead of decelerating.

Control arrangements are known which automatically generate the maximum torque required for each speed switch on the brake. However, such arrangements are relatively expensive and also employ one continuously adjustable event resistance ahead.

There are also known brake circuits for hoist drives where braking is caused by electrical and mechanical means. In. First and foremost, to protect the mechanical brake, it is initially braked with countercurrent and then the drive is finally shut down with the aid of a mechanical brake. The countercurrent braking is therefore carried out using a lowering brake circuit
for hoist drives

Applicant:

LICENTIA Patent -Verwaltungs - G. mb H. _f Frankfurt / M., Theodor-Stern-Kai 1

Dipl.-Ing. Walter Endres, Frankfurt / M.,
has been named as the inventor

loaned to degrade the performance of the mechanical brake.

In contrast, the invention is based on the object of avoiding with certainty that when braking from heavy loads to lower speeds, the loads fall. According to the invention this is achieved by initially braking to low speeds when connected to the mains of the stator braking up to a speed of the drive that is in the stable range of the selected Braking curve lies, is made and then on DC excitation of the stator with simultaneous corresponding circuit of running he resistors and / or corresponding excitation of an electrical controllable braking machine is switched.

In crane hoists or the like, the three-phase asynchronous machine with direct current excitation or with an electrically controllable braking machine should be used small control speeds can be achieved.

In FIG. 1, in an exemplary embodiment for a DC-excited slip ring rotor, the torque M is plotted as a function of the speed η for countercurrent braking (straight line g).

When downshifting, the system first decelerates effectively and quickly to a speed that is definitely in the stable range of the braking curve, and only then, for example, in point X it switches to DC excitation and at the same time to the braking curve that corresponds to the selected braking curve (in the exemplary embodiment br V) Rotor resistances switched. In Fig. 1, the separation between the stable and unstable area of the braking curve br I is indicated by the dash-dotted straight line ζ . The braking made up to point X can, for. B. with the help of a mecha-. niche brake take place. Instead of a mechanical one

009 587/96

Braking is also a braking with countercurrent, expedient.

In the arrangement shown in FIG. 2, the drive motor of a hoist is a slip ring rotor 10 is provided, the rotor resistances of which are switched via the contactors 11 to 13. Inventor measure, the lowering contactor 14 is switched off to reduce the lowering speed to a certain amount and the countercurrent braking is switched on via brake contactor 15. To monitor the speed a speed monitor 17 is provided which, when a selected low lowering speed is reached the brake contactor 15 switches off and thus a separation of the stator from the three-phase network makes and at the same time contactor 16 for direct current excitation of the stator applies voltage. Simultaneously· so that the corresponding rotor resistance stage is switched on via the contactors 11 to 13.

Instead of or in addition to direct current braking, an electrically controllable braking system can be used according to the invention Braking machine, for example an eddy current brake, can be provided. This brake can also are excited at the same time as switching to countercurrent. This increases the braking force. the In this case, too, the countercurrent is switched off when the lowering speed is low.

For monitoring the lowering speed, at which the counter-current braking and the direct-current braking or eddy current brake is switched on, a speed monitor is expediently provided. Instead of this speed monitoring, time monitoring can also be used, for example with the aid of a timing relay.

As drive motors, abrasive belts can be used also squirrel cage with an electrically controllable slip clutch, preferably one Magnetic particle clutch, find use. In this case, the Slip-ring rotor changes the excitation of the slip clutch for speed control.

Claims (6)

Patent claims: 1. Lowering brake circuit for hoist drives with three-phase asynchronous motors, which are energized for braking with disconnection from the mains direct current and / or are provided with an electrically controllable braking machine, the characteristics of which have a stable and an unstable range, characterized in that for braking on low speeds, when the stator is connected to the mains, braking is carried out up to a speed of the drive that _{lies in the stable range of the selected braking curve (^ r 1} ) and then on DC excitation of the stator with simultaneous corresponding switching of rotor resistors and / or corresponding excitation an electrically controllable brake machine is switched. 2. lowering brake circuit according to claim 1, characterized characterized in that for monitoring the lowering speed at which the braking, preferably Countercurrent braking is switched off and DC braking is switched on, a speed monitor (17) is provided. 3. lowering brake circuit according to claim 1, characterized in that a temporal monitoring and switching off the braking, preferably countercurrent braking, and a switchover on DC braking by means of a timing relay. 4. lowering brake circuit according to claim 1, characterized in that for monitoring the Lowering speed at which the braking, preferably countercurrent braking, is down and the excitation the electrically controllable braking machine, preferably eddy current brake, switched on a speed monitor (17) is provided. 5. lowering brake circuit according to claim 1, characterized in that a time monitoring and switching off the braking, preferably countercurrent braking, and switching on the Excitation of the electrically controllable braking machine, preferably eddy current brake, by means of of a timing relay. 6. lowering brake circuit according to claim 1 and following, characterized in that the drive motor a squirrel cage with an electrically controllable slip clutch, preferably Magnetic particle clutch, is provided and this for speed control according to the various Lowered positions is excited. Considered publications:
German Patent Nos. 746 750, 765 379;
U.S. Patent Nos. 1,154,016, 1,684,247. 1 sheet of drawings © 009 587/96 8.60