Easy and quick monitoring of safety brakes

Production around the clock, high part quantities and maximum utilisation of capacity - thermoforming machines for the manufacture of packaging containers made of plastic demand the best performance from their drive systems. In addition, vibrations and impacts are generated within the system, caused amongst other things through the tools which are inserted into the hot plastic foils or plates and which specify the later contours of the moulded parts. In order to guarantee operational and functional safety, precisely in such difficult ambient conditions, reliable monitoring of the safety brakes is essential. Therefore, a manufacturer of thermoforming machines has used the ROBA-brake-checker in their latest generation of machines, trusting in state of the art technology by mayr power transmission.

As on previous thermoforming machines, a risk analysis must also be conducted on this new machine generation according to DIN EN ISO 13849 in concordance with the Machinery Directive. In order to achieve the required degree of diagnosis coverage, the user has up to now deployed electromagnetic ROBA-stop-M safety brakes on previous machines, on which the switching condition monitoring has been conducted using an inductive proximity sensor or a mechanical release monitoring system, i.e. with a microswitch. An additional ROBA-switch rectifier was installed for control of the brakes with overexcitation and a subsequent voltage reduction.

In the latest generation of machines, a ROBA-brake-checker is now being used, which replaces both the mechanical release monitoring and the ROBA-switch, meaning that it unites both functions and also offers further decisive advantages. This is because the ROBA-brake-checker works without the use of sensors, i.e. no microswitch or proximity sensor has to be mounted onto the brake outside for switching condition monitoring, and therefore ROBA-stop-M brakes can be used today in their basic design. In addition, the additional wiring and - depending on the protection class required - any sealing of switches and sensors are no longer necessary. The ROBA-brake-checker therefore guarantees complete freedom of design.

In contrast to systems using switches and sensors, which are exposed to impacts and vibrations due to their installation situation, using the ROBA-brake-checker monitoring takes place from the control cabinet, i.e. in a protected environment. It works without mechanical contacts, with high reliability and wear-free, independent of the cycle frequency. The module assesses the characteristics of the magnetic coil during the brake switching procedure. Because the magnetic coil is a component which is cast permanently into the brake and which is therefore highly durable, impacts and vibrations have no effect on the coil characteristics, and therefore on the reliability of the ROBA-brake-checker.

Detecting errors before they occur

The ROBA-brake-checker module detects when the brake changes condition, i.e. whether the armature disk is attracted to the coil carrier (brake opened) or has dropped (brake closed). The respective switching condition of the brake is emitted by the module via a signal output. On reaching the tension reserve, the ROBA-brake-checker emits a warning signal. In a similar way to the fuel display on a car, which is also able to drive a certain distance after the warning lamp lights up, the brake can also continue to run for a certain operating time. During this time, the machine operator can plan the maintenance - aligned to their working process - in a targeted manner. In addition, the ROBA-brake-checker can detect interruptions in the brake supply line. It is also able to deduce a possible wear reserve through the assessment of current and voltage, or detect unpermitted heat temperatures. In this way, it can find safety-critical conditions prior to their occurrence, and thus guarantees not only maximum operational safety but also increases the productivity of machines and systems.

In addition, the monitoring module ROBA-brake-checker is capable of automatically adapting the overexcitation time. An integrated, automatic mechanism analyses the optimum overexcitation time from the electrical characteristics of the brake, and accordingly regulates this to the set reduction voltage. Using a DIP switch, the automatic mechanism can be switched off and certain, specified values can be entered manually. The ROBA-brake-checker has been dimensioned for an input voltage of 24V or 48V DC, and can control brakes with a coil nominal current of 10A or 5A. The module can be used flexibly for a wide spectrum of ROBA-stop brakes, and can be easily and quickly installed, also into existing systems. Because the switching condition monitoring and brake control are combined with the ROBA-brake-checker in one device, users can also save on investment costs.

Intelligent braking of movements

For applications requiring braking torque regulation in addition to condition monitoring, mayr power transmission provides the braking torque control module ROBA-torqcontrol. It shares the properties of the ROBA-brake-checker and can also change the level of braking torque in operation through targeted influencing of the current and voltage. Devices and machines can thus be evenly and gently decelerated. The ROBA-torqcontrol module offers the possibility of building up control loops and intelligently braking movements -prerequisites for use in smart, networked machines.

For more information about mayr's intelligent brake control module ROBA-brake-checker please visit www.mayr.com.