MOTOR-OPERATED CRANE DRIVE

Abstract

The invention relates to a motor-operated crane drive in which a more rapidly rotating motor (1) drives a more slowly rotating cable drum (3) via a transmission (3). A safety brake (5) is arranged on the more slowly rotating side of the transmission (2). A signal that is used for actuating the safety brake (5) is utilized for initiating an electrical deceleration of the motor (1).

Claims

1.-5. (canceled)

6. A motor-driven crane drive, comprising: a rope drum; a gear unit; a motor driving the rope drum via the gear unit; and a safety brake arranged on a slower-rotating side of the gear unit, wherein a signal serving to trigger the safety brake is used to initiate electric braking of the motor.

7. The motor-driven crane drive claim 6, further comprising a frequency converter configured to control the motor.

8. The motor-driven crane drive claim 6, further comprising a control device configured to generate and determine a timing of the signal for initiating the electric braking of the motor.

9. The motor-driven crane drive claim 8 further comprising an emergency stop switch operably connected to the control device and configured such that upon actuation of the emergency stop switch an emergency stop signal is generated and transmitted to the control device to trigger the signal for initiating the electric braking of the motor.

10. The motor-driven crane drive claim 8 wherein the signal triggered in the control device is split into a first emergency stop signal to activate the safety brake and thereby cause a braking of the rope drum, and a second emergency stop signal transmitted to the frequency converter to cause the electric braking of the motor.

11. A method for operating a motor-driven crane drive, said method comprising: arranging a safety brake on a slower-rotating side of a gear unit placed between a faster-rotating motor and a slower-rotating rope drum; and initiating electric braking of the motor by the safety brake, when an emergency stop signal is activated to trigger the safety brake.

12. The method of claim 11, wherein the signal serving to trigger the safety brake is received in a control device, and further comprising, after receiving the signal the control device generating and determining a timing of an emergency stop signal for initiating the electric braking of the motor, and sending the emergency stop signal for initiating the electric braking of the motor to the motor or a converter supplying the motor.

Description

[0016] The invention is explained below on the basis of an exemplary embodiment with reference to the drawings, in which, schematically and not to scale

[0017] FIG. 1 shows a crane drive, and

[0018] FIG. 2 shows a diagram illustrating the time scales arising during the braking processes.

[0019] FIG. 1 is a schematic diagram, not true to scale, of a motor-driven crane drive, in which an electric motor 1, for example a three-phase motor, drives a rope drum 3 via a gear unit 2. The motor 1 is supplied with electric current via a frequency converter 6.

[0020] A drive shaft 11 of the motor 1 is connected with an input shaft 21 of the gear unit 2 by means of a clutch device 30. A service brake 4 comprising a brake disk 41 connected non-rotatably to the clutch 30 and a brake caliper 40 is arranged on the clutch 30. Brake pads mounted in the brake caliper 40 may act from both sides on the brake disc 41. The service brake 4, on the fast side of the gear unit 2, is designed merely as a holding brake for the stationary drive system.

[0021] A rotational motion of the input shaft 21 of the gear unit 2 is geared down through three gear stages to slower rotational motion of the output shaft 22 of the gear unit 2. A rope drum 3 is connected non-rotatably to the output shaft 22. A safety brake 5 comprising a brake disk 51 connected non-rotatably to the rope drum 3 and a brake caliper 50 is arranged on the rope drum 3. Brake pads mounted in the brake caliper 50 may act from both sides on the brake disc 51. After arrival of an emergency stop signal, the rope drum brake 5 located on the slow side of the gear unit 2 is activated. The rope drum brake 5 engages in a very short time and with very significant force, in order to bring a load transported by the crane to a standstill as quickly as possible.

[0022] In an emergency, for example if a person is present in the hazard zone under a load, a crane driver may actuate an emergency stop switch 70, in order to bring the rope drum to a standstill as quickly as possible. On actuation of the emergency stop switch 70, a first emergency stop signal is generated and transmitted to a control device 80 via a first signal line 7. In the control device the incoming first emergency stop signal triggers a process over the course of which a second emergency stop signal is generated and transmitted via a second signal line 8 to the rope drum brake 5, and a third emergency stop signal is generated and transmitted via a third signal line 9 to the frequency converter 6.

[0023] The emergency stop signal arriving at the rope drum brake 5 there triggers activation of the rope drum brake 5, as a consequence of which rotation of the rope drum 3 is braked to a standstill and the rope drum 3 is kept at a standstill.

[0024] The emergency stop signal arriving at the frequency converter 6 there triggers activation or maintenance of an air gap torque of the electric motor 1 contrary to the direction of rotation of the motor. In the case of generator operation, the kinetic energy of the electric motor 1 is converted into electrical energy and either dissipated as heat via an electrical resistor (rheostatic brake) or fed back into an electric power grid 60 or a storage device (regenerative brake).

[0025] Activation of generator operation of the electric motor 1 leads to electric braking of the motor 1, i.e. the motor 1 itself generates a braking torque directed contrary to the rotational motion thereof. The peak load to be absorbed by the gear unit 1, which is generated in the gear unit 1 by braking of the inert mass of the fast side of the gear unit 1 after activation of the rope drum brake 5, is reduced significantly by electric braking of the motor 1, because the inert mass of the motor 1 does not or at least in part does not come into play as a result of electric braking thereof. The precise level of load reduction depends on the performance of the motor/converter combination, but generally amounts to no less than the simple rated torque of the gear unit 1. This reduction is possible because the converter 6 is regenerative and can feed the kinetic energy of the mechanical system regeneratively back into the grid 60.

[0026] The emergency stop signals sent by the control device 80 are timed such that the engaging of the rope drum brake 5 and the electric braking of the motor 1 takes place at the same time or the electric braking of the motor 1 takes place shortly, in particular in the region of up to a few tenths of a second, before the engagement of the rope drum brake 5. In this way it is ensured that the inert mass to be absorbed by the gear unit 1 is actually reduced. If the electric braking of the motor 1 were namely to be delayed relative to the engagement of the rope drum brake 5, a reduction in load would not be achievable.

[0027] The emergency stop signal which is generated by the emergency stop switch 70 and which serves to trigger the safety brake 5 is used in the control device 80 to generate a further emergency stop signal addressed to the converter 6 and thus to initiate electric braking of the motor 1.

[0028] FIG. 2 shows a diagram illustrating the time scales within which the braking processes take place. In the diagram, torques M are plotted against the time t in the unit ms for a lifting process in which a sudden emergency stop signal occurs. In the diagram, the air gap torque 100 of the motor, the braking torque 110 of the rope drum and the gear unit torque 120 are plotted.

[0029] First of all, a lifting process of a crane, as shown in FIG. 1, takes place: in the electric motor 1 a constant air gap torque 100 is present, which is transmitted to the gear unit 2 and there acts as a constant gear unit torque 120. The braking torque 110 of the rope drum is zero, since the safety brake 5 has not been activated.

[0030] At the time S. roughly at t=100 ms, an emergency stop signal occurs, which triggers motor 1 cutout. The air gap torque 100 of the motor 1 thereby drops immediately to zero. At the same time, the safety brake 5 is triggered by the emergency stop signal.

[0031] Between the time S of the emergency stop signal and the increase in braking torque 110 at the time A, there is a time interval of approximately 200 ms, in which the brake pads move from their resting position onto the brake disk. After the 200 ms, i.e. at the time A, the brake pads rest against the brake disk. From this time the contact pressure of the brake pads against the brake disk increases, which causes the steep rise in the braking torque 110 of the rope drum.

[0032] Between the time S of the emergency stop signal and the increase in braking torque 110 at the time A, the gear unit torque 120 oscillates sinusoidally around a slightly decreasing torque value: the motor torque no longer acts on the gear unit 2, but inertia allows the gear unit 2 to continue rotating. The slight falling trend of the mean gear unit torque 120 results from the only slowly relaxing rope, and the oscillation results from the sudden removal of stress from the gear unit 2.

[0033] As soon as the brake pads of the safety brake 5 are resting against the brake disk, the braking torque 110 of the rope drum increases sharply and reaches its maximum value after approximately 40 ms. The gear unit torque 120 rises at the same time and similarly abruptly, since now the inert mass of the elements of the drive train connected to the gear unit input shaft 21, in particular of the motor 1, the clutch 30 and the service brake 4, act on the gear unit 2 from the front, i.e. via the gear unit input shaft 21.

[0034] From the time B, i.e. the time at which the braking torque 110 on the rope drum has reached its maximum value, this braking torque 110 remains constant at its maximum value, since the safety brake 5 has reached its maximum braking action. immediately after the time B the gear unit torque 120 also reaches its maximum value; this value may be so high that the gear unit 2 is damaged. Once the maximum value of the gear unit torque 120 has been reached, the gear unit torque 120 oscillates sinusoidally around a gently decreasing torque value.

[0035] The present invention allows the maximum value of the gear unit torque 120 to be reduced considerably.