In many industrial handling and automation tasks, workpieces or tools have to be rotated into position. This places great demands on swivel units, with requirements spanning everything from high speed and precise movement to powerful operation and low maintenance. In practice, it is difficult to combine these various requirements, since powerful pneumatics fail to reach the necessary positioning accuracy, while compact electric drives lack the required power. A novel combination of both drive concepts is now setting new standards for swivel units.
When two pneumatic cylinders act via the piston rack on a shaft with pinion, the result is a simple, powerful rotary motion. Depending on the piston surface and pressure, substantial force can be introduced to the shaft. The disadvantage of this approach is that gases are compressible, meaning that it is almost impossible to home in on a very specific position rapidly – even you if spend significant amounts on control valve technology. And if you switch to electric drives, small-footprint solutions usually lack the necessary power.
Schunk, a German-based company specialising in industrial handling, has now solved this primary dilemma with a combination of both drive variants.
For the electric drive components, they have brought micromotor experts FAULHABER, based in Schönaich, on board. The result is a compact, precise and efficient swivel unit.
Powerful high-precision rotation
In the new drive concept, the pneumatics and electromotor complement each other. The pneumatics provide the high power density required, while the electric motor contributes the fast response times and fine controllability. In the SRU 40 Masterdrive, designed according to this concept, in addition to the drives, the necessary control electronics are also integrated, making optimal use of both drives according to their key strengths.
The intelligent drive selection permits short cycle times even with different loads. The servomotor is activated directly after the signal to start from the PLC. With the inherent delay, the pneumatics act as a "turbo" to provide the required torque. This ensures an immediate, soft start-up and powerful acceleration. When decelerating, the pneumatics are responsible for ending the forward momentum, and the electromotor moves the unit precisely into position. Additionally, for the braking process with high loads, the pneumatics act as a soft brake that is adjustable to specified parameters; hydraulic shock absorbers subject to wear are no longer necessary with this design.
Despite the elaborate control system, the swivel unit manages with only two connections: a compressed air connection for filtered air and a control cable from the drive to the control cabinet. Here, a control box takes over the connection to the PLC and the standard 24 V power supply. Thus up to five positions can be set easily via digital inputs and outputs without the need for programming. The impulse from the PLC is then sent to the position in question, and the drive gives a feedback signal after reaching the position. Here, the pneumatic drive ensures a high torque of 13 Nm. The simple control of the DC micromotors means that a swivel range of 180° with positioning accuracy of an impressive 0.03° can be achieved.
Easy to adjust
Modern DC microdrives are well-priced, durable, reliable and – thanks to pulse width modulation (PWM) of the supply voltage – easily adjustable. In this application, a 24 V motor of around 100 W ensures the necessary "smooth precision". At only 4 A current consumption, the drive also permits compact, low-loss activation. Since the motors in four-quadrant operation assume both the drive and braking functions, they are well-suited for positioning tasks. The soft start-up with low loads and the high short-term overload capacity are also advantageous for many drive applications.
The drives with permanently lubricated bearings are completely maintenance-free. Due to the great variety of micromotor models, a standard drive can often be used, as in this case. For special tasks, the motor models in question can be specially tailored to the application as required. Here, it is advisable to involve FAULHABER as early on as possible, the aim being to achieve a maximum level of efficiency for the drive solution – with a minimum of effort. Users can concentrate fully on their core area of expertise, while the engineers in Schönaich/Germany draw on their many years of experience to address all the challenges relating to drive technology.
Modern micromotors are suited to a great variety of tasks, the main focus being on setting objects in motion. Whether as the sole drive source or in a hybrid design together with another drive concept, the only limit placed on state-of-the-art microdrives is the imagination of product developers.
SCHUNK GmbH & Co. KG