Month: July 2016

Press productivity improves with controller upgrade

Guest contributor: Richard Meyerhoefer, Delta Computer Systems

Fastener stamping machine output triples after tuning the motion with a solution from Delta Computer Systems.

Improving the productivity of a manufacturing process by speeding up the operation of an old machine can be very difficult, driving plant managers to purchase new equipment. It’s often possible, however, to replace the control system, maintaining the old mechanics, and get the performance of a new machine for much lower cost. Hydraulics distributor CMA/Flodyne/Hydradyne (CMAFH) of Hanover Park, Illinois, recently assisted in such an upgrade for a manufacturer of fastening components. The machine was a press used to imprint patterns on the surface of metal fasteners with a punch that fits into the bottom of a 4″ bore hydraulic cylinder (Figure 1). As the punch comes down it reshapes the top of the fastener and its edges to provide a locking feature.

Motion controller selection

Figure 1. Diagram showing motion controller connections in the fastener press machine

In the past, the manufacturer used a programmable logic controller (PLC) to operate a two-position, bang-bang valve to drive the cylinder, but company engineers found imprecise results that limited production to around 60-to-70 parts per minute. As a result, the company moved to a proportional valve and closed-loop controller that operated the valve based on cylinder position/acceleration. The controller would open the valve quickly and then back off the valve as the cylinder got closer to making contact with the fastener. This method enabled an increase in production to approximately 140 parts per minute. But to meet competitive pressures, company managers demanded the rate be increased, driving the need for a new electro-hydraulic motion controller.

Company engineers called CMAFH, with whom they had worked on automation solutions for more than 20 years, to recommend a new controller for the company’s old bang-bang machine.

Hooking up the controller

The Delta RMC75E motion controller (Figure 2), recommended by CMAFH engineering manager Norman Dziedzic, accurately controls position and force, to control acceleration with more precision than the closed-loop controller previously used. Dziedzic programmed the motion controller to move the cylinder to a predetermined position while monitoring the force being applied by the punch. When the force reaches a particular value, the controller is switched to force control mode to ensure that adequate force is ultimately applied to the fastener. The old closed-loop control system used position control only, with some input from a load cell within the tool to verify that a certain minimum force was applied to the part.

“The Delta controller operates similar to that, but is easier to control,” says Richard Mellor, engineer at the fastener company. Every motion step made by the other controller was initiated by the PLC, and there was lag time in passing position information. “The beauty of the Delta controller is that the motion program now resides in the controller,” Mellor adds.

Now, the PLC just does overall machine control, triggering the Delta RMC to press the part at the appropriate time. When the pressing operation is complete, the Delta controller knows, based on the position and force ranges inputted to the controller, whether the pressed part is a good part or a bad one, and notifies the PLC. The Delta RMC75E gets cylinder position feedback from a linear magnetostrictive displacement transducer (LMDT) via a synchronous serial interface (SSI) to the controller. To measure force, the system uses a fatigue-rated (rugged) force transducer (shown in Figure 1).

Programming, tuning

Figure 2.  The Delta RMC75E motion controller can control up to two motion axes simultaneously

Dziedzic set up the motion program initially, and he fine-tuned the loop parameters working with a fastener company engineer. The two also developed the code to implement quality testing of the finished parts.

“I find the Delta very easy to program, but I have 30 years in as a controls engineer. If you’ve had anything to do with PLC or message display packages, it’s relatively intuitive to find your way around,” Mellor says

For tuning the motion, Dziedzic relied heavily on Delta Computer Systems’ Plot Manager software, which allows an engineer to view multiple key motion parameters versus time on a single graph (Figure 3). The plot shows three press cycles, where the red curve is the actual position of the press cylinder, the blue curve is the actual velocity of the cylinder, and the force being applied by the die to the work piece is shown by the black line. The cyan line is the target cylinder position. When the motion system is perfectly tuned, the actual cylinder position curve overlaps the target position, indicating that any positioning error caused by the mechanical aspects of the system – for example, the compressibility of the fluid or the friction of the moving parts – has been compensated for by the control algorithm. In Figure 3, the flat yellow line indicates the command force which must be applied to the part to make the press operation successful. The circle marked A highlights the point in time when the actual position (red line) begins to deviate from the target position (cyan line) as the tool comes into contact with the part. This is also when the force (black line) begins to climb. Then, at point B, the change in actual velocity (blue curve) shows force control taking over from position control. Area C in the plot shows when the actual force meets the target command force to signal a successful operation. Area D shows harmless motion transients that are caused by retracting the cylinder quickly to prepare for pressing the next part.

Using the Plot Manager, motion characteristics that occur too quickly to be visible to the naked eye can be analyzed and corrected if necessary, enabling the manufacturing process to be accelerated.

Results

Figure 3.  Delta’s RMCTools plot Manager software shows axis position and force versus time, enabling precise tuning of the motion.

One of the fastener company’s other key requirements on the controller upgrade project was to provide a means of accessing process data using the controller in order to do a pass/fail test on the finished parts.

“We track final position reached and maximum force achieved,” Dziedzic says. Previously, the company needed an external analog device to do this. Now, the Delta RMC75E eliminates this need by making process parameters available for the PLC to read directly over Ethernet. “The fact that the Delta controller can do this in addition to controlling the cylinder provides a huge benefit to them.”

“We have been very happy with the performance increase we have gotten with the Delta motion controller,” Mellor adds. “Even if we hadn’t gotten the performance, Delta’s ease of use in system setup and tuning would have made the difference.”

With the Delta RMC75E controlling the operation of the cylinder, the machine can now process up to 180 fasteners per minute.

“We can move faster because we have more control over the proportional valve, yielding tighter control loops and better control of the gain in the system,” Mellor says.

Another advantage of using the Delta RMC is operation repeatability; the controller is able to control the force exerted in each cycle to a tolerance of ±40 lb out of 10,000 lb applied.

ABOUT US

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CMA/Flodyne/Hydradyne is an authorized  Delta Computer Systems distributor in Illinois, Wisconsin, Iowa and Northern Indiana.

In addition to distribution, we design and fabricate complete engineered systems, including hydraulic power units, electrical control panels, pneumatic panels & aluminum framing. Our advanced components and system solutions are found in a wide variety of industrial applications such as wind energy, solar energy, process control and more.

Enhancing Stepper Motor Systems with Linear Encoders

Guest contributor, Henry Menke, Balluff

Tabletop automation is a trend that is gaining momentum, especially in the fields of medical laboratory automation and 3D printing. Both of these applications demand a level of linear positioning accuracy and speed that might suggest a servomotor as a solution, but market-driven cost constraints put most servos out of financial consideration. New advances in stepper motor design, including higher torque, higher power ratings, and the availability of closed-loop operation via integrated motor encoder feedback are enabling steppers to expand their application envelope to include many tasks that formerly demanded a servo system.

Meeting the Demand for Even More Accurate, More Reliable Positioning

As tabletop automation development progresses, performance demands are increasing to the point that steppers systems may struggle to meet requirements. Fortunately, the addition of an external linear encoder for direct position feedback can enhance a stepper system to enable the expected level of reliable accuracy. An external linear encoder puts drive-mechanism non-linearity inside the control loop, meaning any deviations caused by drive component inaccuracy are automatically corrected and compensated by the overall closed-loop positioning system. In addition, the external linear encoder provides another level of assurance that the driven element has actually moved to the position indicated by the number of stepper pulses and/or the movement reported by the motor encoder. This prevents position errors due to stepper motor stalling, lost counts on the motor encoder, someone manually moving the mechanism against motor torque, or drive mechanism malfunction, i.e. broken drive belt or sheared/skipped gearing.

Incremental, Absolute, or Hybrid Encoder Signals

bmlThe position signals from the external encoder are typically incremental, meaning a digital quadrature square wave train of pulses that are counted by the controller. To find a position, the system must be “homed” to a reference position and then moved the required number of counts to reach the command position. The next move requires starting with the position at the last move and computing the differential move to the next command position. Absolute position signals, typically SSI (synchronous serial interface) provide a unique data value for each position. This position is available upon power-up…no homing movement is required and there is no need for a pulse counter. A recent innovation is the hybrid encoder, where the encoder reads absolute position from the scale, but outputs a quadrature incremental pulse train in response to position moves. The hybrid encoder (sometimes referred to as “absolute quadrature”) can be programmed to deliver a continuous burst of pulses corresponding to absolute position at power up, upon request from the controller, or both.

For more information about magnetic linear encoder systems, visit www.balluff.us.

CMAFH resources for Balluff Linear Encoders

Secure Protection from Attacks, Malicious Software and Unauthorized Access

Guest contributors: Gerrit Boysen and Mariam Coladonato, Phoenix Contact

High system availability is very important in process engineering, because ongoing processes must not be interrupted. A fence is a physical, easily identifiable safety measure to secure systems from unauthorized persons. In addition to such physical protections, implementing IT security practices is also becoming more important.

The current trend toward interconnectivity is driving the growing need for IT security in process engineering. Not only is there an increasing number of horizontal interconnections from one system to another, but also the field level is more connected to the office level. In addition, all levels are using more and more Ethernet components. The good news is that this interconnection increases efficiency and reduces costs. The downside of this, however, is that it also increases the risk that malicious software will quickly spread throughout all areas of a company.

In light of this information, process-engineering systems are repeatedly being threatened by new security gaps and a growing number of malicious programs. The computers and control systems used in industrial networks must have much more extensive protection from attacks, malicious software, and unauthorized access than they have so far (Figure 1).

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Figure 1: The Process Analysis Center is protected by a firewall.

The security strategies used in conventional office IT, however, usually are not designed for industrial systems. Industrial networks require special protective measures. The IT systems used in production environments differ fundamentally from those used in office environments in four ways.

  1. Patches cannot typically be applied to industrial systems
  2. Industrial systems use special protocols such as OPC Classic, which are not used in the office world
  3. Large systems can have structurally identical modular assemblies with identical IP addresses
  4. Production systems often require different firewall rules and standards during maintenance and in the event of remote servicing

Office PCs usually have virus scanners that perform security updates at regular intervals. These measures do not normally work for industrial systems for a few reasons. Sometimes, the manufacturer of the operating systems or applications used in the industrial sector no longer provides security updates. In addition, test measures must be performed on industrial PCs before each operating system, antivirus software, or application update, and this cannot be done efficiently in terms of operation.

The use of specific industrial firewalls can protect these non-patchable systems against attacks from outside the network. To do this, hardware-based firewall appliances are connected between industrial PCs and outside networks. Another advantage of using external security hardware is that the system’s resources do not have to be used for security tasks (Figure 2).

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Figure 2: Security example from the process industry.

Targeted restriction of network communications

With firewalls, the user can configure the protocols and ports that can be used to access the protected systems. This can prevent or at least limit the attempt of an attacker to gain access to the network through insecure ports. The Stateful Packet Inspection Firewall approach is an ideal way to manage these systems. This approach uses rules to filter incoming and outgoing data packets in both directions: from the outside to the protected internal network and vice versa. Based on the protocol, source addresses and ports and destination addresses and ports can be used to limit network communications selectively to a defined scope required for production. Here, the Connection Tracking function identifies the response packets on permitted connections and lets them through.

When selecting a suitable firewall, the engineer must ensure that the selected firewall understands any protocols used in the particular industry. Otherwise, reliable protection cannot be guaranteed. For example, office firewalls typically do not support industrial protocols such as OPC Classic, so they cannot provide appropriate protection for the application.

While conventional firewalls cannot reliably protect data traffic via OPC Classic, industrial variants – such as one with a license for OPC Inspector – can provide a suitable solution. The firewall checks the OPC Classic communications data packets and filters them precisely, based on Deep Packet Inspection. For this purpose, the Stateful Inspection principle is also applied to OPC Classic data. This means that the firewall identifies the port changes negotiated in the OPC Classic protocol and approves them dynamically. In this context, it inspects whether a port opened by OPC is used within a timeout period and whether the data traffic moving through this port corresponds to the OPC protocol. This method provides high-access security (Figure 3).

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Figure 3: Deep Package Inspection in the OPC protocol.

Unique and clear mapping to virtual external networks

Complex production sequences are typically structured into networked, largely standalone cells. For an efficient design of the engineering, documentation, and cell operation, the use of identical IP addresses for all systems of a single type proves to be advantageous. If all communications are initiated from the internal cell networks, several identical systems can be connected with simple masquerading NAT (Network Address Translation) routers to the operator’s production network. If the higher level network also needs to establish a connection to the individual cell nodes, however, this solution is not sufficient, because the cell nodes cannot be addressed from the outside. In this case, the user requires a router that can map internal machine networks universally or selectively to unique virtual external networks using 1:1 NAT.

Because of this, an industrial firewall offers the so-called 1:1 NAT routing function, in addition to the pure NAT routing. OPC Inspector, mentioned above, allows this NAT function for the OPC Classic protocol. This sets it apart from conventional office firewalls and other industrial firewalls.

Event-controlled (de)activation of firewall rules

Different firewall rules and standards have advantages in different situations. This is because during production operation or maintenance and remote system servicing, different connections are allowed or forbidden. In practice, the user usually solves the problem by summarizing the various firewall requirements in a set of rules. This procedure inevitably lowers the level of security, because the firewall rules allow all connections required for the different operating states, even if they are not required for the current operation.

An industrial firewall solves the problem by implementing a Conditional Firewall. This function allows the firewall rules to be activated or deactivated depending on events. A variety of events – such as an externally connected button, switch, control window in a web interface, API command line, or establishing or disconnecting a VPN (Virtual Private Network) connection – can be selected to trigger a specific firewall rule (Figure 4).

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Figure 4: Secure remote access to the system.

Summary

The requirements placed on a firewall in a production zone are different from those in the office world. Therefore, using an industrial firewall with a NAT function can support the individual, simple segmentation of networks. This allows the Defense-in-Depth concept based on the ISA-99 and IEC 62443 international standards to be implemented even in systems using the OPC Classic protocol.