Integrated Small Servo Drives for Synchronized Motion Control Applications Dipl. Wirt.-Ing. Markus Britsch, Baumüller Kamenz GmbH, Technical Director Volker Banholzer, M.A., Baumüller Nürnberg GmbH, Director Marketing Dr.-Ing. Peter Heidrich, Baumüller Nürnberg Electronic GmbH & Co. KG, Director Development Abstract - For integrating small servo drives and actuators in the integrated automation world of large servo drives, there is currently no all-encompassing solution (i.e., an integrated synchronised fieldbus and standardised operating tools are basically missing). The solution to this integration task comes in the form of a small servo drive that exhibits the characteristic features of the large servo drives (i.e., synchronised fieldbuses and a standardised device control via fieldbus or a standard service interface, among others). This ensures a simple integration in the machine-automation environment and an integrated diagnostics capability and allows for replacing classical actuators and small drives by costoptimised small servo drives. Integrated synchronised fieldbuses, integrated small servo drive. 1. Problem For integrating small servo drives in the integrated automation world of large servo drives with respect to actuators, there is currently no all-encompassing solution (i.e., an integrated synchronized fieldbus for the complete range of servo drives is basically missing). If a small drive features a fieldbus, it must generally be addressed differently than that of a large servo drive. A similar situation applies if the small drive does not feature a fieldbus, since it would then, generally, require different operating tools. 2. State of the art The current implementation, for example, of infeed, adjustment and proportioning tasks continues to predominantly feature solutions with mechanical, manually-operated mechanisms, actuators with fixed start and target positions, and stepping motor drives. In part, mechanical revolution counters are still used to check these actuators. Each one of these approaches features disadvantages, such as the missing control for mechanical, manually-operated mechanisms or limited functionality. In addition, the required limit switches and sensor technology create expenses for cabling, component matching and troubleshooting. All approaches share the non-existent or insufficient integration in the automation structure of the corresponding production system. 3. Innovative Solution To be able to implement production systems in a safer, faster, more integrated and more precise way, the small servo drive with the essential characteristics of a large servo drive represents a more futureoriented approach. The required characteristics include: Synchronized fieldbuses
Active motor braking with regenerative braking to the DC link A standardized device control via fieldbus or via a standard service interface. This allows for a simple integration in the automation architecture of the machine and ensures an integrated diagnostics capability. Small servo drives typically have an electrical output of less than 750 W (less than 1 HP). Frequently, only safety extra-low voltages are used. Similar to classical large servo drives, small servo drives are also available as control cabinet versions. In addition, an integrated design has been implemented for small servo drives in which the electrical machine, the position sensing technology and the drive electronics form a compact unit. Furthermore, this variant revolutionizes the automation world through extensive savings for project planning, space requirements and implementation. These savings are based on the fact that the combination of electronics and motor as a compact unit requires wiring only the communication and supply cable, and the project planning effort is essentially restricted to the dimensioning of the power supply. Commissioning is facilitated on principle through the drive unit that is perfectly matched. Due to the mounting of the integrated small servo drives directly onto the machine, an enclosure of IP 54 and, optionally, IP 65, is a necessary requirement of these drives. Figure 1 shows an example of a small servo drive from Baumüller; on the left side is a control cabinet version, on the right side is an integrated small servo drive. Figure 1: Small servo drives from Baumüller. Left: Control cabinet version b maxx 2400. Right: Integrated small servo drive b maxx 2300. Table 1 shows how typical combinations for the integrated small servo drives can be implemented.
Size Unit Example 1 Example 2 Motor shaft height mm 28 M 36 S Rated speed 1/min 2200 3000 Standstill torque Nm 1.3 1 Rated torque Nm 1.25 0.95 Position encoder Hall or incr. Hall or incr. DC link voltage V 12 to 59 12 to 59 Max. mech. output power W 300 300 Fieldbus: CANopen with sync message Yes Yes Fieldbus: CANsync In preparation In preparation Table 1: Typical designs of integrated small servo drives. Size Unit Example 1 Example 2 Motor shaft height mm 36 S 36 M Rated speed 1/min 3000 3000 Standstill torque Nm 1 2.2 Rated torque Nm 0.95 1.9 Position encoder Hall or incr. Resolver, incr. absolute, SinCos DC link voltage V 12 to 59 up to 380 V (1x 230 VAC) Max. mech. output power W 300 700 Fieldbus: CANopen with sync message Yes Yes Fieldbus: CANsync In preparation Yes Table 2: Typical designs of small servo drives as control cabinet variants. 3.1. Implementation of uniform integration The uniform integration in the automation environment of the machine is possible because of a connection to a master control system and a corresponding fieldbus master by means of a synchronized fieldbus. In principle, the three approaches consisting of Drive PLC, Controller PLC or Soft PLC, which can be flexibly and individually matched to the needs of each individual machine, are possible as control systems. The three approaches can be used to represent decentral, central, as well as hybrid architectures on a uniform platform. 3.2 Approach with synchronized CANopen CANopen has established itself as an economical fieldbus that is supported by many manufacturers. In the meantime, there are also PLCs from different manufacturers with CANopen master interface modules. By using the standardized CANopen sync message, they are capable of establishing a synchronization on the CANopen fieldbus with only a few µs of jitter. Using the synchronized CANopen fieldbus then enables the covering of many applications that rely on synchronized movements. Figures 2 and 3 show examples of how small drive systems can be integrated in motion control and automation solutions with a Drive PLC or Controller PLC using the standard CANopen fieldbus so that a
uniform drive system is created that encompasses servo drives with high output as well as small servo drives. The following applies to the programmer of the motion control and automation application: All servo drives, including the small servo drives, feel the same. Figure 2: System interconnection with a drive-based PLC via CANopen. Here, it is implemented as b maxx-drive PLC in the controller b maxx 4400 in interconnection with b maxx 3400, the integrated variant of the small servo b maxx 2300 and b maxx 2400.
Figure 3: System interconnection via CANopen with a Controller PLC as an independent PLC, together with integrated small servos. 3.3 Approach with CANsync For applications that pose even higher demands on synchronous movements, the use of the highsynchronous CANsync is possible. With this fieldbus, the synchronization jitter is reduced to < 1 µs by using a hardware-bound sync line. A corresponding system with Drive PLC is shown in Figure 3. The same applies here: Using the same fieldbus in the large servo drives and the small servo drives creates a system that must be treated equally by the programmer with respect to motion control and automation applications regaedless of whether it is a servo drive with only a few watts and 24-V DC link voltage, or a servo drive with the power of several kilowatts and high DC link voltages (310 V to typically 760 V).
Figure 4: System interconnection with Drive PLC and CANsync. 4. Use and Practical Experience as well as Advantages of the Uniform Servo Series up to the Small Servo Drive In an implemented application with eight servo axes, six of the eight drives could be replaced by small servo drives with synchronized fieldbus. In the end, it contributed to a cost-optimized implementation of this application so that the competitiveness of the automated machine could be significantly improved.
Figure 5.1: Architectural diagram of the application. Original solution with eight servo drives. Figure 5.2: Architectural diagram of the application. Solution with two servo drives and six small servo drives.
In addition, the integration increased the flexibility of the architecture. This, in turn, resulted in new perspectives for the implementation of automation tasks. 5. Summary and Outlook Based on the constantly increasing requirements for machines, particularly in the areas of availability, accuracy, synchronization of all movements, including existing auxiliary drives, continuity of project planning and programming, and the accompanying increasing automation of the machines, an even more far-reaching integration of small drives in the conventional automation world can be expected in the future. In this context, faster commissioning, diagnostics capability and flexibility will play an important role. It can also be assumed that new, high-performance fieldbuses and fieldbuses based on industrial real-time Ethernet (e.g., on the basis of EtherCAT), will make their entrance for small servo drives and allow for further innovations in the application of small servo drives.