EP0513954A2 - Method of compensating the torque in a driving apparatus of a pilger mill - Google Patents

Abstract

The invention relates to a method of compensating the torque at the drive of a pilger mill roll stand, in particular a cold pilger mill roll stand, moved backwards and forwards linearly via a crank mechanism. In order to avoid hitherto existing disadvantages and to provide compensation for torque which reliably and with little constructional outlay avoids generator operation of the motor of the driving apparatus, i.e. torque acting on the motor in the direction of rotation of the motor, it is proposed that the speed curve of the crank mechanism, determined by calculation from the kinematic dimensions, the moving masses and the external loads, be fed to the drive motor as the set point speed curve.

Description

The invention relates to a method for torque compensation on the drive of a rolling stand of a pilgrim step rolling mill, which is linearly reciprocated via a crank drive, in particular a cold pilger rolling mill.

The oscillating movement of the rolling stand of a pilgrim step rolling mill has the consequence that the kinetic energy of the rolling stand varies greatly over the path. Without countermeasures, the crank mechanism would want to overhaul the engine twice per period, i.e. bring it into generator operation. The resulting periodic alternation of engine and generator operation has a wear-promoting effect on the engine and also increases the energy consumption of the rolling mill. The energy that the engine extracts from the crank mechanism during generator operation must be fed back to the crank mechanism during the subsequent engine operation.

However, because the electrical energy generated in generator operation cannot be used in motor operation, this energy portion has the character of an apparent power for the operator of the rolling mill, which increases the operating costs unnecessarily.

In order to avoid the periodic alternation between generator and motor operation, two different designs have proven their worth. For example, it is known from German patent 10 64 461 to supplement the crank mechanism which generates the movement of the roll stand with a similar crank mechanism which is operated out of phase by 90 degrees. This way, there can be a constant exchange of kinetic energy between the two crank mechanisms. Although this method has the advantage that the crank speeds and the crank torque, and thus also the engine speed and engine torque, are almost constant over a movement cycle, it has the disadvantage that the mechanical engineering expenditure is very great. This also applies to the space requirement, because deep foundations are generally required. Finally, higher order inertial forces are difficult to balance.

Another way of solving the problem is to compensate the torque by interposing unevenly geared transmissions. If you accelerate a crank drive that moves a roll stand to a certain speed and then disconnect it from the drive, the speed of the crankshaft will change periodically. In the case of freedom from friction, this statement will apply for any length of time. If you now place an unevenly geared transmission between the drive and the crankshaft, which at the constant drive speed on the output side has exactly the speed curve that the crank drive in non-driven state, the crank mechanism can also be driven at a constant engine speed and constant engine torque. The intermediate gear must convert the constant speed into a variable speed, which corresponds to the free speed curve of the crank mechanism. Since the speed fluctuations of the crank mechanism depend on the respective speed, the transmission behavior of the intermediate gear must be variable.

An intermediate gear that is actually used for torque compensation is the universal joint, which can be adapted to the speed fluctuations by changing the articulation angle in the joint (German Patent 20 30 995).

The last-mentioned method also has the disadvantage that a great deal of design effort is required to enable the torque compensation to be set to a specific speed. When changing to a different operating speed, the engine returns to generator mode if the torque compensation is not automatically adjusted. In addition, the influence of the load on the torque compensation cannot be taken into account.

Based on the described prior art and the disadvantages described, it is the object of the present invention to provide a torque compensation which safely and with little construction effort avoids the generator operation of the motor of the drive device, i.e. torques acting on the motor in the direction of motor rotation.

To achieve the object, it is proposed according to the invention that the speed curve of the crank mechanism, which is calculated from the kinematic dimensions, the moving masses and the external loads, is specified as the target speed curve for the drive motor.

Favorable embodiments of the invention are described in the subclaims.

The invention has recognized that an optimal torque compensation can be achieved if the target speed of the engine does not become less than the current actual speed. Generator operation is safely avoided if the target speed of the drive motor always corresponds to the speed to which it is being accelerated or decelerated by the load. To ensure this, it is necessary to know the speed curve that is set. This can be calculated precisely if the kinematic dimensions, the moving masses and the external loads are known. The calculated speed curve, which a friction-free crank drive would have in the state driven with constant torque, is given to the drive motor as the desired speed curve.

The invention has the effect that acceleration or braking torques no longer have to be applied by the engine. In the stationary area, the engine only works against friction losses and external loads. If there is no external load, the engine only works against the almost constant friction losses, the engine torque is then approximately constant.

The proposed system is operated with a fast computer which, depending on the respective crank position, calculates the crank speed in advance and communicates it to the drive system. Systems of this type which meet the necessary control speed and control accuracy are state of the art.

• a) das reduzierte Massenträgheitsmoment Jred des Kurbeltriebes,
• b) die potentielle Energie Epot des Kurbeltriebes,
• c) die auf ein reduziertes Drehmoment ML an der Kurbel umgerechnete Last

als Funktion des Kurbelwinkels φ gespeichert. Ausgehend von der Kurbelwinkelgeschwindigkeit ω₀ in der Position φ₀ der Kurbel werden für die übrigen Kurbelwinkel φ die Winkelgeschwindigkeiten der Kurbel mit folgender Formel ermittelt.

To be able to calculate the speed, are in the calculator

• a) the reduced moment of inertia Jred of the crank mechanism,
• b) the potential energy epot of the crank mechanism,
• c) the load converted to a reduced torque ML on the crank

stored as a function of the crank angle φ. Starting from the crank angle speed ω₀ in the position φ₀ of the crank, the angular speeds of the crank are determined for the other crank angles φ using the following formula.

wobei das als konstant angenommene reduzierte Motormoment

dem mechanischen System Kurbeltrieb während einer Periode so viel Energie zuführt, wie ihm durch die übrigen äußeren Lasten entzogen wird.The working surplus ΔW (φ) results in

${\text{ΔW (φ) =}}_{\text{O}}{\text{∫}}^{\text{φ}}{\text{[M}}_{\text{Mot, red}}\text{- ML (φ)] dφ}$

the reduced engine torque assumed to be constant

During a period, the mechanical system of the crank mechanism supplies as much energy as is withdrawn by the other external loads.

This reduced engine torque is only a calculation variable, it should not be confused with the actual engine torque. The actual engine torque will differ from the ^" reduced engine torque" at least by the proportion for overcoming frictional losses.

mit $\overline{\text{n}}$

als vorgegebenem Drehzahlmittelwert hinreichend genau erfüllt wird.The starting value ω₀, on the basis of which the prediction of the angular velocity curve ω (φ) is based, must be determined iteratively. To do this, change ω₀ until the condition

With $\overline{\text{n}}$

as a predetermined mean speed value is met with sufficient accuracy.

Claims (3)

Method for torque compensation on the drive of a rolling stand of a pilgrim step rolling mill, in particular a cold pilger rolling mill, which is linearly reciprocated via a crank drive,
characterized,
that the drive motor of the calculated speed curve of the crank mechanism from the kinematic dimensions, the moving masses and the external loads is specified as the target speed curve. Method according to claim 1,
characterized,
that to calculate the target speed values, the reduced moment of inertia of the crank mechanism, the potential energy of the crank mechanism and the load converted to a reduced torque on the crank are stored as a function of the crank angle in a fast computer and based on the crank angle speed in a specific position of the crank the angular velocities for the other crank angles are calculated, the result of the processing of the respective speed setpoint being communicated to the engine of the drive device. Method according to claim 1,
characterized,
that the starting value of the crank angle speed in the starting position of the crank angle is determined iteratively.