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Effective protection of machine tools

Release date: 2018-10-15 14:30:47 Visits: 515

An important electrical parameter in machine tools is the effective power of the motor. This parameter can be accurately monitored using Phoenix Contact''s Contactron Motor Manager, and high overload and low load operating conditions are immediately detectable by this instrument. Since the motor manager can promptly issue alarms and maintenance prompts before the motor fails, it can effectively protect the machine tool and significantly improve the usability of the machine tool.

In industrial applications, electric motors are generally used to start production. In general, it is protected by a motor current protector that protects against the length of the overcurrent, or by a motor protection switch that is overload protected according to the magnitude of the load. However, what happens to the motor when the cooling fan of the motor is reversed, or when the cooler is clogged and normal cooling cannot be achieved?

FDT/DTM software for parameter assignment, troubleshooting and production data collection

Current monitoring is often insufficient
There is no doubt that when the temperature of the motor rises to a certain critical value, it will cause failure of the motor. As a solution, a thermistor can be placed in the winding of the motor and this thermistor can be connected to a control switch that can cut off the motor current when the motor temperature is too high. The thermistor and the temperature-controlled switch together constitute the overall protection of the motor. However, this protection scheme has little protection for its subsequent mechanical equipment or mechanical structure, and it cannot be avoided that it will still fail under the worst working conditions.
The main reason for motor failure is that many users reduce the inventory and reserve too few motor variants. In practice, about 90% of the motor''s working load is only 40% to 60% of the rated power, and it does not work within its optimal operating characteristics. The overcurrent protection devices of these motors are set according to the rated power on the motor nameplate and are set according to the parameters of the motor within the optimum operating characteristics. When the load changes, even small changes are reflected in the power factor and efficiency; the motor current changes almost unchanged. Despite this, the mechanical device can still be overloaded, but the problem is not shown in the pure current monitoring system. This can have serious consequences for machine tools: motor-driven mechanical devices are severely damaged and expensive.

Detect effective power to improve protection of machine tools
The Contactron series of motor managers developed and manufactured by Phoenix Contact have an effective power harvester that protects the motor and machine equipment (Figure 1). Since only the effective power is linearly varied over the entire power range of the motor, the magnitude of the motor output torque can be known at any time by such a linear change. On the other hand, only the two factors of power factor at overcurrent and low load can protect the motor. The motor manager monitors all variable parameters, such as current, voltage and power factor; and calculates the effective power based on the detected data after 6.6 ms, so that it can also determine load changes that are very short.
According to this monitoring method, it is possible to quickly issue an alarm message or cut off the power supply of the machine tool. The detected data that can draw the motor running curve truly reflects the working condition of the machine tool; clearly shows the difference between the theoretical observation data and the theoretical calculation data. With this Contactron Motor Manager, all the machine tool components and instruments installed behind the motor, such as bearings, mechanical components, etc., can be taken into account together and displayed, and can be quickly secured (Figure 2 ). Compared to pure current protection, effective power based monitoring can also provide safety protection at low loads, such as pump run-off operation, etc., to accomplish tasks that have long been required to assist with the use of an effective power monitor.
The saved start-up curve is an important part of the equipment''s operating conditions and can be used as a reference for equipment aging, dirt levels or wear conditions. Using this curve, it is possible to accurately determine all the monitoring parameters, the upper and lower limit values of the monitoring, and the alarms, prompts or power supply cutoffs, parameter assignments, etc. corresponding to these limit values. The manager''s parameter assignment is performed using DTM (Device Type Manager) software, which is compatible with FDT (Field Device Tools), such as Phoenix Contact''s automation management software AutomationXplorer. In this way, the motor manager can be integrated into various engineering tools or control systems in a unified and stable manner.
Only the effective power allows the entire range of upper and lower limit loads of the machine tool to be monitored. As a protective switch for machine tools, it guarantees high availability of machine tools and thus high production capacity. With its effective power monitoring function, it can detect faults and interferences during use in time to avoid equipment downtime. As the basis for the calculation of technical data, it is based on electrical data: electrical data obtained by using the motor as a sensor. Time-consuming and labor-intensive additional sensors, even expensive sensors such as pressure sensors, flow sensors or differential pressure sensors, can be omitted. Other electrical parameters, such as the operating time of different gears, the total working time of the machine tool, and the energy used, can be collected while optimizing maintenance.

Easy and convenient refill with motor power cable
With the integrated current converter''s motor manager, you can directly monitor the 16A current motor and install it without taking up too much space. When the motor current is larger, a special module can be used, combined with an external current converter, to monitor the motor of each power class. Therefore, the use of this instrument to monitor the motor and machine equipment becomes very simple: only the cable that supplies the motor is used. In this way, it is also possible to supplement the assembly of such a motor manager in the existing equipment, and it is possible to provide the user with accurate machine equipment operation data in the future.
The disconnection of the three-phase electrical load is performed by a special mechanical relay or a semiconductor relay that is contactless and powered by the Contactron series of digital outputs of the motor manager module. At this point, the motor manager provides safe monitoring and protection of the pump, console or cutting machine and evaluates the electrical energy required for each device. In this monitoring process, whether the motor manager is powered by itself or powered by fieldbus, this task can be done well.
With the help of the Profibus fieldbus gateway certified by Phoenix Contact and certified to the DPV1 specification (EN 50170), up to 32 motor manager modules can be easily and conveniently mounted on the T-Bus slot of the connector. It is possible to communicate with each other (Fig. 3) without complicated wiring. Compared with other solutions commonly found on the market, this solution can significantly reduce investment costs and save installation space in electrical cabinets. All production data can be transferred to the upper control system via FDT/DTM and processed by the upper control system. In addition, the Profibus fieldbus gateway also supports fault-safe functions: the DTM parameter assignments can be used to influence faults and errors in the Profibus fieldbus system for safe protective power-off control. In addition, this instrumentation also has digital I/O terminals that can be used to communicate with other components. The gateway integration in the Profibus DPV1 system can be assigned by the GSD instrument description method, and the FDT/DTM used is much more flexible in the parameter assignment, monitoring and troubleshooting of the motor manager and the entire machine tool.