Intelligently monitored and controlled brakes
19-02-2018
New modules for the monitoring and braking torque control of ROBA-stop® safety brakes
They can quickly and easily monitor safety brakes or facilitate the even and smooth deceleration of machines and devices – the intelligent ROBA®-brake-checker and ROBA®-torqcontrol modules by mayr® power transmission make brakes fit for the challenges of the Industrie 4.0 government initiative. Furthermore, they create the prerequisites for preventative fault recognition and maintenance, and thus for the increased productivity of machines and systems.
When driving a car, drivers use the footbrake to gently decelerate the vehicle in a targeted manner. Nobody would come upon the idea to pull the handbrake or parking brake when a car is driving at speed. The same applies for devices and machine applications featuring dynamic braking procedures; where controlled, even deceleration is often desired. However, unlike automotive brakes, electromagnetic safety brakes only have two design-dependent operating conditions as “braking torque present” and “braking torque cancelled”, and therefore each braking procedure is implemented with the maximum-available braking torque, determined through the spring pressure. On devices such as material handling truck, the loads on which can differ, the brake has up to now always been dimensioned to the maximum load. However, it is not always expedient to operate with full braking torque. As a result, in case of a partial load, a more severe deceleration can lead to damage of the transportation goods or even to blocking or skidding of the wheels. In applications such as film wrapping machines, in which the torque changes as the wrapping radius increases and decreases, limitation of the tensile forces through a correspondingly-adjusted braking torque is often significant for the protection of the material, but also for the machine design. For this reason, mayr® power transmission has now developed the ROBA®-torqcontrol module, an intelligent and economically-attractive solution, using which adjustable braking reactions are possible and machines can be brought to a defined standstill.
Gentle and well-aligned braking
The prerequisite for this electronic braking torque control is that the system measures operating conditions such as loading, speed or acceleration, and converts these measurements into a specification signal for the ROBA®-torqcontrol module. “If the module is used in a closed control loop system, then it is possible to run defined deceleration ramps, i.e. bringing the machine to a standstill gently and in accordance with the requirements”, explains Frank Timmler from Electronics Development at mayr® power transmission. “Using this module, it is possible for us to continuously change the contact force on the brake linings, and therefore the braking torque, during operation. In addition, in the case of applications, which require a constant braking torque within narrow tolerance limits, negative influences on the braking torque consistency can be compensated through such braking torque control. Our customers particularly value the fact that the ROBA®-torqcontrol module can be extremely easily integrated into superordinate control and regulation systems, and that no undesired feedback occurs on the control and regulation systems”.
The ROBA®-torqcontrol module can either be operated with 24V or 48V DC voltage, and controls brakes with a nominal coil current of 10A or 5A. With two digital inputs, the resulting contact force on the brake linings can be specified to 30%, 50%, 75% or 100% of the nominal spring force. Alternatively, a stepless analogue specification signal of 0 to 10V (30-100%) is possible.
Electronic braking torque control
In order to control the brakes, the ROBA®-torqcontrol module specifically influences the current and voltage, and therefore the internal physical values. Besides the parameters of friction radius, coefficient of friction and the number of active friction surfaces, the braking torque of a safety brake is also calculated from the sum of the spring force and magnetic force. “The maximum torque of the closed brake is achieved when the magnetic force is equal to zero, and only the springs are taking effect”, says Frank Timmler. “If the magnetic force is then specifically applied against the spring force, then direct influencing of the effective spring force and therefore the braking torque is possible. We can already specify the desired braking torque with the module prior to application of the brake”.
Permanent brake monitoring and preventative maintenance
Besides the ROBA®-torqcontrol module for controlling electromagnetic safety brakes, mayr® power transmission has developed an intelligent solution for monitoring the brakes with the ROBA®-brake-checker module. Both modules are based on the same functional principle. The ROBA®-brake-checker module exclusively serves to monitor the brakes; the ROBA®-torqcontrol module shares this monitoring function, and can also control the brakes. Users can select the appropriate solution depending on the application case. Both modules operate without sensors; instead they use the brake itself, i.e. the electromagnetic actuator, as the sensor. In this way, the modules analyse the physical conversion processes in the brake, i.e. the conversion from electrical to magnetic and then to mechanical energy. These processes generate reactions, and can be identified through the assessment of current and voltage. Through the analysis of current and voltage, the modules recognise the movement of the armature disk, and thus know the condition of the brake. In addition to the switching condition, the modules can also determine the temperature, wear and tension path or tensile force reserve, i.e. whether the magnet still has sufficient force to attract the armature disk. With the new modules, a significantly larger number of processes can be depicted by the monitoring than was hitherto the case, for example using Hall sensors, which monitor the energisation or the magnetic field, or microswitches or inductive proximity sensors. On reaching the tensile force reserve, the ROBA®-brake-checker and ROBA®-torqcontrol emit a warning signal, early enough so that a defined operating time of the brake is still possible. Within this time, the machine operator can undertake specific maintenance in coordination with their work process – maintenance with foresight, so to speak.
The ROBA®-brake-checker is now available in a design for AC voltage. In addition, another version of the module will also in future take on the supply of the brake, and as a result, replace the rectifier. Switching condition monitoring and brake control are therefore combined in one unit.
Condition monitoring without switches
Due to the fact that ROBA®-torqcontrol and ROBA®-brake-checker operate without sensors, i.e. no microswitches or proximity sensors have to be attached to the exterior of the brake for switching condition monitoring, all possible weaknesses of today’s micro switches, such as incorrect adjustment, limited service life etc., are eliminated. Furthermore, safety brakes can be used in their basic design, and, if required, can be painted over without any problem. Additional wiring is rendered obsolete, and, depending on the Protection, so is the sealing of the switches and sensors. The modules therefore ensure complete design freedom. This is very different to the solutions with switches and sensors, which are exposed to impacts and vibrations due to the installation position on the brake. The modules monitor or control from the control cabinet, i.e. from a protected environment. They operate without mechanical contacts and with high reliability, and remain wear-free, independent of the cycle frequency.