Device for sewer pipe inspection and / or rehabilitation, with a DC motor driving a working machine

Abstract

Device for sewer pipe inspection and / or rehabilitation, with a DC motor driving a working machine, which is connected to an electrical voltage source by means of an intermediate circuit having a braking resistor, characterized by a step-down converter connecting the braking resistor to the intermediate circuit and a controller increasing the output voltage of the step-down converter when a predetermined input voltage applied to the step-down converter is exceeded.

Description

The invention relates to an apparatus for sewer pipe inspection and / or rehabilitation, with a direct current motor driving a working machine. In particular, the invention relates to a device for canal pipe inspection and / or rehabilitation, with a direct current motor driving a working machine, which is connected to an electric voltage source by means of an intermediate circuit having a brake resistor.Such a device with a working machine designed as a cable, cable, chain or hose winch is known from public prior use. The known winch is used, for example, for winding up a flushing hose, wherein it is necessary to brake, with the winch, the advancement of the flushing hose, which is caused by the water repulsion occurring at the flushing nozzle. However, even when heavy sewer pipe devices are simply lowered into a shaft of a pipe system, the winch must be braked.The engines used in the known winch are permanent-excitation direct current (DC) motors or brushless direct current (BLDC) motors, which are supplied with a direct voltage, which is generated, for example, by a switched-mode power supply. This voltage is called an intermediate circuit voltage because it represents a voltage level between the mains voltage and the motor voltage. For motors with an electrical power of up to a few hundred watts, this voltage is often designed as a safety low voltage (SELV) in order to ensure electrical safety.The motors used for this purpose are usually controlled with pulse width modulation (PWM), wherein the voltage for the motor is controlled with a frequency in the kHz range. The inductance of the motor smoothes the motor current and results in a motor speed corresponding to the average value of the applied voltage.In the applications mentioned at the beginning, there is also an operation in which the motor operates as a generator. The motor is thereby mechanically driven. For example, when lowering a load or when the carriage of a device for sewer pipe inspection and / or rehabilitation is travelling downhill or when pulling a flushing hose by water impulse drive.If the motor is provided with a fixed pulse duration with a duty cycle of, for example, D=0.5, the motor would output approximately 50% of its nominal rotational speed during motor operation and thereby draw power from the intermediate circuit and supply it to the mechanical side. If a mechanical drive acts in such a way that it increases the rotational speed, a mechanical braking action is established by the motor now acting as a generator. Mechanical energy is converted into electrical energy, which is shown as current flowing from the motor drive into the charging capacitors of the intermediate circuit voltage. A disadvantage of this is that the voltage in the intermediate circuit rises and can lead to the destruction of electronic components.To meet this problem, a brake resistor is usually connected to the intermediate circuit voltage, which permanently converts an appreciable electrical power into heat. However, it is disadvantageous that the use of such a braking resistance is poor in energy efficiency and heat balance of the apparatus.It has therefore already been proposed that the braking resistor be connected only in the operating state in which the operation of the motor as a generator can occur-for example in the case of a hoist in "downward" operation.Thus, the power converted on average can be reduced, for example, by the resistor being connected only in so-called chopper operation-as shown in FIG. 1 according to a circuit known from the prior art. In this case, it is monitored how high the intermediate circuit voltage is, wherein, when a critical value is exceeded, a resistor is connected, which discharges the capacitors of the intermediate circuit until a lower limit value is reached. A disadvantage of this is, in turn, that the intermediate circuit voltage fluctuates continuously between the two threshold values.If this fluctuation is not desired, a shunt regulator can be used as known for limiting the intermediate circuit voltage, as a result of which some of the power in semiconductors is converted into heat. In this case, the power semiconductors used must be designed such that they are protected from the second breakdown (secondary breakdown). However, here too there is a disadvantage, namely that an arrangement of a plurality of semiconductors requiring a relatively large amount of space is required, wherein the semiconductors can also be cooled only very laboriously.It is therefore the object of the invention to provide a device for sewer pipe inspection and / or repair with a circuit which produces overvoltage protection of the intermediate circuit, which is of simple construction and space-saving design, enables uniform limiting of the intermediate circuit voltage which is precisely matched to the load case and does not require complex cooling.This object is achieved according to the invention by the apparatus for sewer pipe inspection and / or rehabilitation having the features of claim 1. The dependent claims represent advantageous embodiments of the invention.The basic idea of the invention is to control a step-down converter (step-down switching regulator) supplied from the intermediate circuit voltage, to the output of which the braking resistor is connected, in such a way that the intermediate circuit is loaded to such an extent that the intermediate circuit voltage levels to an acceptable value. For this purpose, the intermediate circuit voltage is measured and fed to the feedback of the switching regulator, wherein the output voltage of the step-down converter is increased above a predefined value when a predetermined input voltage present at the step-down converter is exceeded and thus a voltage is present in the intermediate circuit.The step-down switching regulator, which acts like a regulating transformer for direct current, can transform the resistor to the intermediate circuit voltage. The resistance "appears" thereby with values between infinity to almost down to the nominal value of the resistance.Unlike in conventional applications of a step-down converter in which the pulse duration is increased if the output voltage of the step-down converter is too low, for example by means of pulse width modulation (PWM), according to the present invention, the pulse duration is increased if the input voltage applied to the step-down converter is too high and the overvoltage is dissipated to the brake resistor.An advantage of the present invention is that only as much electric power is converted to heat as is really necessary to brake the motor. If further loads load the intermediate circuit voltage, no further relief of the intermediate circuit may be required and the brake resistor is inactive.A further advantage of the invention is that the intermediate circuit voltage during braking rises only slightly and there is an only slight rotational speed difference between the rotational speeds during braking and during driving of the working machine. Moreover, the DC link voltage is stably maintained at a desired predetermined value, resulting in a uniform motor rotation speed without jerks or fluctuations.The power loss, i.e. the power obtained from the mechanism, is for the most part implemented in a cost-effective, robust resistor which can be freely selected within certain limits and can be easily cooled. In extreme cases, this can be a heating rod in the water tank. The semiconductors used for the configuration of the electronics only convert very little power, so that they do not have to be cooled additionally.According to the invention, therefore, a device for canal pipe inspection and / or rehabilitation is proposed, with a direct current motor driving a working machine, which direct current motor is connected to an electrical voltage source by means of an intermediate circuit having a braking resistor, wherein a step-down converter connecting the braking resistor to the intermediate circuit and a regulator increasing the output voltage of the step-down converter when a predetermined input voltage present at the step-down converter is exceeded are provided.As a working machine of the device for canal pipe inspection and / or rehabilitation, in particular a winch, especially a cable, rope, chain or hose winch, is provided. The hose or cable winch with a hose or cable wound thereon is configured for supplying a sewer pipe inspection and / or rehabilitation unit, wherein such a unit is specifically a carriage or a sliding system which has a camera, a tool for sewer pipe machining or a device for sewer pipe machining, a flushing nozzle or a shut-off device.According to a further preferred embodiment of the invention, the working machine is a milling cutter.Preferably, at least one additional electrical device connected to the intermediate circuit is also provided, which is supplied with electrical energy by the intermediate circuit and buffers an overvoltage in the intermediate circuit to a certain extent as an electrical load.Finally, the regulator is configured to increase the output voltage of the step-down converter preferably by means of a method for pulse width modulation (PWM).FIG. 2 shows a particularly preferred embodiment of a circuit suitable for implementing the device according to the invention. The circuit comprises a direct current motor M which is connected to an electrical voltage source by means of an intermediate circuit having a braking resistor R1. The brake resistor R 1 is connected to a step-down converter connected to the intermediate circuit, wherein a regulator increases the output voltage of the step-down converter by means of pulse width modulation (PWM) when a predetermined input voltage present at the step-down converter is exceeded.The sequence of the regulation realized by the circuit provides that, in the event of an increase in the intermediate circuit voltage, the difference UDIFFbetween a predetermined reference value Urefand the actual intermediate circuit voltage UZ* decreases, as a result of which the pulse width modulation is increased such that the power in the brake resistor R 1 increases. As a result, the DC link voltage is limited to a predetermined value.

Claims

Device for sewer pipe inspection and / or rehabilitation, having a direct current motor which drives a working machine and is connected to an electrical voltage source by means of an intermediate circuit having a braking resistor, characterized bya step-down converter which connects the braking resistor to the intermediate circuit, and a regulator which increases the output voltage of the step-down converter if a predetermined input voltage present at the step-down converter is exceeded.Device according to Claim 1, characterized in that the regulator is designed to increase the output voltage of the step-down converter by means of pulse width modulation (PWM).Device according to one of the preceding claims, characterized byan electrical device connected to the intermediate circuit.Device according to one of the preceding claims, characterized in that the working machine is a winch.Device according to one of Claims 1 to 4, characterized in that the working machine is a milling cutter.

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