Fast, precise and safe

Proven safety technology for flow wrapping machinexs

Whether it’s powder, liquid or solid: many products cut a better figure in a plastic pouch. Flow wrapping machines not only seal a wide range of products, they also persuade through a whole assortment of attractive pouch types. The machines work quickly and reliably, can be converted to new tasks in no time at all and take up very little space. Pilz safety technology ensures there's no conflict between productivity and safety.

With impressive speed the machine pulls the plastic web over several guide rollers and on to the forming shoulder: it is here that the film web is made into a tube package, which can be filled with pieced, powder, paste, granulated or liquid products as required. A discharge belt pulls the wrap down along the wall of the filling tube, the longitudinal sealing tool seals the film tube vertically. Once filled, the transverse sealing tool seals the packaging horizontally and the blade separates the bags. The benefits of flow wrapping: It can be adapted to suit almost any packaged product perfectly, it enables vacuum packaging and, because the film is transparent, the type and quality of the contents is clearly visible. Whether you need a stand-up, flat or side-sealed pouch: flow wrapping machines can now handle an impressive variety of shapes and solutions.
Rovema Verpackungsmaschinen GmbH is based in Germany and offers a wide range of packaging and cartoning machines for the most wide-ranging products and application areas. The Rovema Group has branches worldwide and currently employs around 700 staff. Flow wrapping machines are a key component in the Rovema portfolio. “The demand today is for intelligent packaging solutions which set standards and are based on the respective requirements at the point of sale. At the same time they must be economical and future-proof", says Walter Maurer, who is responsible for electrical design and standardisation at Rovema.

Perfect packaging in the shortest possible time
The medium-sized company supplies intermittent horizontal/vertical, continuous vertical and double axis flow wrapping machines with a linear motor. The machines are always modular and open for future tasks and trend changes.  All the flow wrapping machines have compact dimensions and can be operated in stand-alone mode as well as in a network with other plant and machinery.

As shown, the packaging material on the VPL flow wrapping machine is fed from rollers and the machine operates vertically: The product to be packaged is fed in to the bag via a collection container and down-tube; the filling, sealing and separating process runs continuously. A non-wearing linear motor is the main drive for the transverse sealing station. Some of the outstanding features of the VPL flow wrapping machine include: its wide format range with high performance, the ability to store individual production programs, freely programmable sealing times and high sealing pressures, plus the vacuum film draw down unit which guarantees consistent bag lengths even with extremely thin films (from 20 µm). The high pressure of the transverse sealing tools means that the sealed seams are especially tight. The use of special magnesium alloys for moving parts minimises the mass moment of inertia and increases output. If necessary it is also easy to integrate additional features such as pulse welding, a zip strip applicator for producing re-closable bags, edge profiling and online diagnostics via modem.

Safe, efficient processes
High availability and highly automated processes require an efficient safety management in the background, which will not only exclude any risk to operators in the event of a fault but will also prevent serious damage to the machine. However, safety-related equipment must not work to the detriment of productivity. In other words: safety technology is intended to protect the operator from injury, but must not obstruct him in his work any more than is necessary. In issues concerning safety, Pilz has enjoyed an excellent reputation in the mechanical engineering sector for many years.  “We choose Pilz because the company is the recognised manufacturer for safety technology on the market. That’s why our machines only leave this factory fitted with Pilz safety solutions”, stresses Walter Maurer. As with all their other flow wrapping machines, the VPL is fitted with PNOZ safety relays. When these are operated, the machine comes to an immediate stop.  Non-contact electromagnetic safety switches PSENmag monitor the sliding gates and covers to ensure they are securely locked, the safety relays evaluate the signals. Should an operator open one of the access gates during the filling phase, the machine will immediately switch to a safe condition.

Rovema can now look back on fifteen years of co-operation with the safety specialists from Ostfildern near Stuttgart. One of the reasons for the successful business partnership is that the development of new packaging solutions always goes hand in hand with the integration of modern safety solutions. When it comes to new and continuing developments, Pilz is one of the first at the table as a partner for safety. “Our partnership is characterised by the quality and reliability of the products, the expertise of Pilz's external sales engineers and, finally, trusting co-operation", says Walter Maurer, summing up. An excellent basis for some good business in the future.

Q. What challenges or hurdles still need to be addressed with safe motion.

A. The standards provide the performance criteria for more sophisticated applications, but there are still many opportunities to implement the more complex applications that are now permitted. In robotics, the most challenging applications involves systems that continue to operate in the present of operators. The collaborative operating mode of maintaining a safe distance between the robotic arm and the operator is yet to be realized. Also, yet to be achieved, is the mode of operation in which the robotic arm force, torque and momentum is limited to inherently safe levels.

The advantage of safe motion, is that it allows the user a closer proximity to the actual process. With safe motion (whether it's safe speed, position or torque), if you can guarantee that the robot/drive is doing exactly what it's intended to (ie. working in a restricted space, at a restricted speed or is at stop), you can reduce and even eliminated your "safe distance" requirements. This would allow the operator to essentially work hand-in-hand with the motion component, increasing production time, reducing floor space and giving the operator a more friendly & ergonomic working environment.

Q. How do safe motion systems work? What role does advance motion control technology play?

A. Reliability theory has been applied to adjustable speed drive technology to define the reliability required for safety applications. There is an acceptance in industry for concept of integrity levels. Higher CPU power, reliability of components and a high level of diagnostics to detect dangerous faults before a failure can prevent a safety function from occurring has allowed these functions to be realized. Application of redundancy and diversity to complex control systems provides a means to predictable and acceptable failure rates.

What is the concept of safe motion? How does it apply to robotics?

Safe motion is the capability of providing motion control functions at an integrity level high enough to reliably provide risk reduction in safe dependent applications. An integrity level is the measure of the predicted failure rate of a control function. Risk, the possibility of harm in relationship to the potential degree of severity, must be reduced to a tolerable level in a safety application. A given integrity level ensures the possibility of harm occurring is sufficiently reduced to be tolerable for a safety related function. These integrity levels and design requirements are now defined in IEC 61800.

Safe motion extends the safeguarding of hazardous motion beyond the traditional dropping of power to the motors when personnel are exposed to a hazard. With safe motion, these are some of the new safe functions available by allowing power to continue to flow to the drives and to the motors:

• Safe torque off
• Safe controlled deceleration to a stop
• Safe operational stop (safe stand still)
• Safely limiting speed or torque
• Monitoring a position or maintaining a speed 

Protective measures implemented in traditional control systems such as reduced speed and hold-to-run functions can be further enhanced through this higher integrity.

In robotics, new applications are now available to the user. The international standard ISO 10218, for robotic safeguarding, is defining new applications for safe motion.

Setting safety related axis limits and defining safety zones in three dimensional spaces is allowing easier reduction of the restricted space of a robot to provide maximum clearance while minimizing the work cell.

ISO 10218 allows for collaborative operation between the robot and the human. In this application the robot may be allowed to stay in automatic, with power available to the motors and possibly continue its motion. The robot may safely limit its speed and if necessary top in a safe standstill mode (safe operational stop) while the operator works on a part in the robots gripper. A safe operational stop is characterized by the halting of motion, but keep torque output on the motors to resisting external forces. Coupled with sophisticated presence sensing technology, all the variations of this application have not been thought of yet.