Motor-driven crane drive and method for its operation

Abstract

Motor-driven crane drive comprising a motor (1) and a frequency converter (6) for controlling the motor (1), wherein the motor (1) drives a rope drum (3) via a gearbox (2) and a safety brake (5) is arranged on the slower rotating side of the gearbox (2), wherein a signal for triggering the safety brake (5) is used to initiate an electric braking of the motor (1), and a control unit (80) for generating and timing the signal to initiate an electric braking of the motor (1).

Description

[0001] The present invention relates to a motor-driven crane drive and a method for operating such a crane drive.

[0002] DE 3838058 A1 (Mannesmann AG) 10.05.1980 and EP 1 710 199 A1 (Shanghai Zhenhua Port Machinery Co. Ltd.) 11.10.2006 disclose motor-driven crane drives in which a high-speed motor drives a slow-speed rope drum via a gearbox. In these drive trains, it is known to arrange a service brake on the "fast side" of the gearbox, i.e. acting on the high-speed gearbox input shaft, and a safety brake on the "slow side" of the gearbox, i.e. acting on the slow-speed gearbox output shaft. Service brakes are rarely used as stopping brakes in the electrically braking systems known today, but rather serve to hold the load safely. Safety brakes serve as additional protection for the system, e.g. in the event of a gearbox shaft breakage. Since the safety brake is usually located on a flanged pulley of the rope drum, i.e.Located at the load-side end of the rotating drive train, it is also called a rope drum brake. Since the safety brake is capable of stopping and holding the load in addition to the service brake, it is also called an auxiliary brake.

[0003] From the document DE 695 11 674 T2, a method for stopping a winch is known. The winch is used to wind up and down a crane rope and has a motor connected to a winch drum via a reduction gear. The motor is powered by an inverter and is arranged between the reduction gear and an electromagnetic brake, which is designed to decelerate the motor. The winch is designed such that, upon stopping, motor control is terminated when the motor speed is zero after a torque command to the motor has been reduced to zero for a certain period of time, following the issuance of a braking command to the electromagnetic brake, which is directly coupled to the motor.

[0004] There are different methods for stopping a lifting or lowering operation in crane drives. In all cases, a crane drive must have an emergency stop that can prevent an imminent or actual danger. Directive 2006 / 42 / EC of the European Parliament and of the Council of May 17, 2006, on machinery and amending Directive 95 / 16 / EC, defines an emergency stop in the Annex, Section 1.2.4.3, as a stopping in an emergency such that the dangerous operation is brought to a halt as quickly as possible without creating additional risks.

[0005] DIN EN 13135:2013-05 “Cranes - Safety - Design - Equipment requirements” in Chapter 5.3.3.1 states that when the emergency stop of category 1 is activated, the service brake must be applied automatically after the electrical braking has brought the movement to a stop.

[0006] Especially in the case of an emergency stop or emergency shutdown, it is common practice to activate the rope drum brake on the slow side of the gearbox. This brake engages with a very short dead time in order to bring the load transported by the crane to a standstill as quickly as possible. During this braking process, the rotating mass on the axis of the high-speed motor shaft, in particular the motor, coupling and brake drum or disc of the service brake, must be absorbed by the gearbox. This can result in the gearbox experiencing a load peak many times the nominal torque. The resulting torque peaks require the gearbox to be designed larger than the maximum static load of the crane would require. Nevertheless, the load peaks are sometimes so large that the service life of the gearbox is shortened.

[0007] Vöth, Stefan, Hoists with safety brakes, parts 1-3, in: Hebezeuge Fördermittel, trade journal for technical logistics, ISSN 0017-9442, Berlin: Huss-Medien GmbH, 55 (2015), issue 3, pages 150 to 152; issue 4, pages 192 to 194; and issue 5, pages 254 to 255, www.hebezeuge-foerdermittel.de, suggests reducing the load on the drive train in the event of an emergency stop or emergency shutdown by ensuring that the service and / or safety brake intervenes as simultaneously as possible with the engine shutdown or that the safety brake and service brake intervene simultaneously or in a coordinated manner.

[0008] One object of the invention is to reduce the load acting on the gearbox during an emergency stop.

[0009] One solution to the problem is a crane drive with the features specified in claim 2. Another solution to the problem is a method with the features specified in claim 4. It is also possible for a corresponding method to be carried out in the event of an emergency stop.

[0010] The crane drive is a motor-driven crane drive. The crane drive consists of a drive motor, a gearbox, and a cable drum. The term "cable drum" encompasses all other types of rotating lifting devices that use chains, belts, etc.

[0011] The gearbox is connected between the drive motor and the cable drum in such a way that the rotation of the drive motor is translated into a slower rotation of the cable drum. The gearbox thus divides the crane drive into a faster-rotating part, also known as the faster-rotating side of the gearbox, and a slower-rotating part, also known as the slower-rotating side of the gearbox.

[0012] A safety brake is located on the slower-rotating side of the gearbox. The safety brake can be a disc brake mounted on the cable drum, or a shoe or drum brake. In the crane drive, a signal used to trigger the safety brake is used to initiate electrical braking of the drive motor, i.e., to generate a torque opposite to the current direction of rotation of the drive motor. This generates a torque that reduces the motor speed and thus supports the effectiveness of the safety brake. The signal used to trigger the safety brake is also referred to as an emergency stop signal.

[0013] The method involves operating a motor-driven crane drive in which a faster-rotating drive motor drives a slower-rotating rope drum via a gearbox. A safety brake is arranged on the slower-rotating side of the gearbox. A signal used to trigger the safety brake, particularly due to the actuation of an emergency stop switch, is used to initiate electrical braking of the drive motor.

[0014] If the motor generates a braking torque at the same time as or shortly before the safety brake is activated, the inertial mass to be braked by the safety brake, and thus the peak load in the gearbox, is reduced considerably. The exact amount depends on the performance of the motor-inverter combination, but is generally no less than the nominal torque. This is possible because the converters on crane drives are generally capable of regenerating the motor's kinetic energy back into the grid.

[0015] Alternatively, the motor's kinetic energy can be converted into thermal energy using a braking resistor. It is also possible to store the potential energy extracted from the load in a mechanical storage system, such as a spring or flywheel.

[0016] The invention reduces the load acting on the gearbox during an emergency stop. As a result, less gearbox damage occurs, and gearboxes or gearbox components can be smaller. This primarily brings economic benefits and, potentially, increased drive availability.

[0017] In the following, the invention is explained using an exemplary embodiment with the aid of the drawing. It shows schematically and not to scale Fig. 1 a crane drive, and Fig. 2 a diagram illustrating the time scales occurring during braking.

[0018] Fig. Figure 1 shows a schematic, not to scale, motor-driven crane drive in which an electric motor 1, e.g., a three-phase motor, drives a cable drum 3 via a gear 2. The motor 1 is supplied with electrical power via a frequency converter 6.

[0019] A drive shaft 11 of the engine 1 is connected to an input shaft 21 of the transmission 2 by means of a clutch device 30. A service brake 4 is arranged on the clutch 30. The service brake 4 has a brake disc 41 connected in a rotationally fixed manner to the clutch 30 and a brake caliper 40. Brake pads mounted in the brake caliper 40 can act on the brake disc 41 from both sides. The service brake 4 on the fast side of the transmission 2 is designed only as a holding brake for the stationary drive system.

[0020] A rotary motion of the input shaft 21 of the gearbox 2 is translated through three gear stages into a slower rotary motion of the output shaft 22 of the gearbox 2. A cable drum 3 is connected to the output shaft 22 in a rotationally fixed manner. A safety brake 5 is arranged on the cable drum 3 and has a brake disc 51 connected in a rotationally fixed manner to the cable drum 3 and a brake caliper 50. Brake blocks mounted in the brake caliper 50 can act on the brake disc 51 from both sides. Upon receipt of an emergency stop signal, the cable drum brake 5 located on the slow side of the gearbox 2 is activated. The cable drum brake 5 engages very quickly and with very great force in order to bring a load transported by the crane to a standstill as quickly as possible.

[0021] In an emergency, e.g., if a person is in the danger zone below a load, a crane operator can activate an emergency stop switch 70 to bring the cable drum to a standstill as quickly as possible. Upon activation of the emergency stop switch 70, a first emergency stop signal is generated and transmitted via a first signal line 7 to a control unit 80. In the control unit, the incoming first emergency stop signal triggers a process during which a second emergency stop signal is generated and transmitted via a second signal line 8 to the cable drum brake 5, and a third emergency stop signal is generated and transmitted via a third signal line 9 to the frequency converter 6.

[0022] The emergency stop signal arriving at the cable drum brake 5 triggers an activation of the cable drum brake 5, as a result of which rotation of the cable drum 3 is braked to a standstill and the cable drum 3 is held at a standstill.

[0023] The emergency stop signal arriving at the frequency converter 6 triggers the activation or maintenance of an air gap torque of the electric motor 1 that is opposite to the direction of rotation of the motor. During generator operation, the kinetic energy of the electric motor 1 is converted into electrical energy and either dissipated as heat via an electrical resistor (resistance brake) or fed back into a power grid 60 or a storage device (regenerative brake).

[0024] Activating generator operation of electric motor 1 results in electrical braking of motor 1, i.e. motor 1 itself generates a braking torque opposite to its rotational movement. The load peak to be absorbed by gearbox 1, which is generated by braking the inertial mass of the fast side of gearbox 1 after activation of cable drum brake 5 in gearbox 1, is significantly reduced by electrical braking of motor 1 because the inertial mass of motor 1 is not, or at least partially, affected by its electrical braking. The exact extent of the load reduction depends on the performance of the motor-inverter combination, but is generally not less than one times the rated torque of gearbox 1. This reduction is possible because converter 6 is capable of regenerating and can feed the kinetic energy of the mechanics back into grid 60 in a generator-like manner.

[0025] The emergency stop signals sent by control unit 80 are timed so that the engagement of cable drum brake 5 and the electrical braking of motor 1 occur at the same time, or the electrical braking of motor 1 occurs shortly, particularly within a few tenths of a second, before the engagement of cable drum brake 5. This ensures that the inertial mass to be absorbed by transmission 1 is actually reduced. If the electrical braking of motor 1 were delayed compared to the engagement of cable drum brake 5, a load reduction would not be achievable.

[0026] The emergency stop signal used to trigger the safety brake 5, which is generated by the emergency stop switch 70, is used in the control unit 80 to generate a further emergency stop signal addressed to the converter 6 and thus to initiate electrical braking of the motor 1.

[0027] Fig. Figure 2 shows a diagram illustrating the timescales on which the braking processes occur. The diagram plots torques M over time t in ms for a lifting process with a sudden emergency stop signal. The diagram shows the air gap torque 100 of the motor, the braking torque 110 of the cable drum, and the gear torque 120.

[0028] First, a crane is lifted, as in Fig. 1, instead: In the electric motor 1, there is a constant air gap torque 100, which is transmitted to the gearbox 2 and acts there as a constant gearbox torque 120. The braking torque 110 of the cable drum is zero because the safety brake 5 is not activated.

[0029] At time S, approximately at t = 100 ms, an emergency stop signal is issued, which triggers the shutdown of motor 1. As a result, the air gap torque 100 of motor 1 immediately drops to zero. At the same time, the emergency stop signal triggers the safety brake 5.

[0030] Between the time S of the emergency stop signal and the increase in braking torque 110 at time A, there is a period of approximately 200 ms during which the brake pads are moved from their rest position to the brake disc. After these 200 ms, i.e., at time A, the brake pads are in contact with the brake disc. From this point on, the contact pressure of the brake pads on the brake disc increases, causing the steep increase in braking torque 110 of the cable drum.

[0031] Between the time S of the emergency stop signal and the increase in braking torque 110 at time A, the gear torque 120 oscillates sinusoidally around a slightly decreasing torque value: the motor torque no longer acts on gear 2, but inertia causes gear 2 to continue rotating. The slightly decreasing trend of the mean value of gear torque 120 results from the cable now slowly relaxing; the oscillation results from the sudden relaxation of gear 2.

[0032] As soon as the brake pads of the safety brake 5 contact the brake disc, the braking torque 110 of the cable drum increases sharply and reaches its maximum value after approximately 40 ms.

[0033] At the same time and in a similarly abrupt manner, the transmission torque 120 increases since the inertial mass of the drive train elements connected to the transmission input shaft 21, in particular the engine 1, the clutch 30 and the service brake 4, now act on the transmission 2 “from the front”, ie via the transmission input shaft 21.

[0034] From time B, i.e., the time at which the braking torque 110 on the cable 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 effect. Immediately after time B, the transmission torque 120 also reaches its maximum value; this value can be so high that the transmission 2 is damaged. After reaching the maximum value of the transmission torque 120, the transmission torque 120 oscillates sinusoidally around a slightly decreasing torque value.

[0035] By means of the present invention, the maximum value of the transmission torque 120 can be significantly reduced. List of reference symbols 1 engine 2 gearboxes 3 rope drums 4 Service brake 5 Safety brake 6 frequency converters 7 First signal line 8 Second signal line 9 Third signal line 11 Drive shaft 21 Gearbox input shaft 22 Output shaft 30 Clutch 40 brake caliper 41 brake disc 50 brake caliper 51 brake disc 60 Power grid 70 emergency stop switches 80 control unit 100 air gap torque 110 Braking torque 120 transmission torque A Time B Time M torque

Claims

[1] Motor-driven crane drive, comprising a motor (1) and a frequency converter (6) for controlling the motor (1), wherein the motor (1) drives a cable drum (3) via a gear (2) and a safety brake (5) is arranged on the slower rotating side of the gear (2), wherein a signal serving to trigger the safety brake (5) is used to initiate an electrical braking of the motor (1), and a control device (80) for generating and timing the signal to initiate an electrical braking of the motor (1). [2] Method for operating a motor-driven crane drive, in which a faster-rotating motor (1) drives a slower-rotating cable drum (3) via a gear (2) and a safety brake (5) is arranged on the slower-rotating side of the gear (2), wherein an emergency stop signal serving to trigger the safety brake (5) is used to initiate electrical braking of the motor (1), wherein the signal serving to trigger the safety brake (5) is received in a control unit (80), the control unit (80) generates and times a signal for initiating electrical braking of the motor (1) after receiving the signal, and sends the signal for initiating electrical braking of the motor (1) to a motor or a converter feeding the motor.

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