Machinedesign 1435 0112 Modularity 0 0

Modularity making motion engineering a snap

Jan. 1, 2012
Standardized subcomponents play an increasingly important role in motion designs, because modular parts and unifying networks reduce investment costs and the time needed to commission moving machinery.

Modular systems are based on standardized individual components that can be combined in different ways to form moving machinery, while reducing the amount of planning, design, and commissioning by system integrators, plant designers, and users. Interchangeable motion components also boost stability, while concurrently allowing modifications and expansions for reconfiguration when a design's purpose changes.

Consider one typical system — the Deprag Compact Assembly Module (DCAM), manufactured by Deprag Inc., with U.S. headquarters in Lewisville, Texas. The DCAM's first iteration assembled mobile phones, abolishing expensive and time-consuming hand assembly: One Swedish cell-phone manufacturer commissioned the first DCAM Weasel assembly platform — and the first 100 were put to use on cell-phone assembly.

At MOTEK 2011 in Stuttgart, engineers presented a new iteration. Jürgen Hierold of Deprag explains, “Until now, every DCAM has been custom, so they took a long time to produce — from initial consultation, through design engineering, to the manufacturing stage — and that degraded delivery times.” In contrast, new modular DCAMs can be deployed in a variety of assembly and production tasks, while a height-adjustable base plate ensures production and operator safety. Production parts are either manually loaded (using a sliding part nest or rotary index table) or automatically by means of a linear transfer mechanism. X and Y axes have tooth-ring drives and (if needed) are augmented with a ballscrew-driven Z-axis. Axes are ultimately driven either by three-phase stepper or servomotors.

DCAM Version A reaches 400 mm in the X axis, and 250 in the Y axis. In version B, both the X and Y axes travel up to 600 mm. The optional Z axis has an effective working range of 150 mm — useful for applications in which several processing points (or paths) must be completed quickly — for assembly, pliable and hard-plate labeling, monitoring the presence or position of components, and dispensing, joining, and marking.

Engineers at Schunk Inc., Morrisville, N.C., are also pursuing modularity. Via adapter plates, many of their gripping modules connect for thousands of application variants. For linear motion and gantry setups, a pneumatically driven line gantry (for payloads of 5 kg), two electrically driven line gantries, and two electrically driven room gantries (for up to 20 kg) sport stroke lengths tailored to particular applications.

For support structures of flexible design, pillar profiles abound. In both electrically driven and pneumatically driven gantries, the servo drives, energy supply, mechanic connections, and sensors are all integrated.

No matter the supplier, Schunk engineers recommend asking the following questions when modularity is a major design goal.

  • How big is the selection of modules for a given family of motion components? Which sizes, weights, and movement ranges are covered? Which drive types does the program comprise? What kind of performance do the modules allow? Is it easy to choose the right module? Does the program also include connecting and add-on elements?

  • Do the modules have uniform interfaces?

  • How are the modules controlled? How difficult is the integration into machines and plants?

  • Does the manufacturer offer CAD data for every module? For assembly groups, does the manufacturer preconfigure components?

  • How much energy do modules consume?

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Connectivity and network conformity

No assembly is truly modular until its communications are standardized as well. Reconsider the Deprag DCAM: It allows up to 199 inputs and outputs, and supports up to three programmable axes, electrical components and relays for controls and safety, and myriad communications modules. Why must it be compatible with so many networks? Protocols (especially those based on Ethernet) have proliferated in recent years. Leading Ethernet-based networks now include EtherCAT, SERCOS, Powerlink, PROFINET, and Ethernet/IP, to name a few. However, some networks diverge from Ethernet flavors for various reasons.

One example is Mechatrolink, supported by the Mechatrolink Members Association (MMA), Waukegan, Ill. Mechatrolink is the most common motion control network in Asia — interconnecting devices such as servomotors, servo amps, and I/O and linking them to PLCs, PACs, and other motion controllers.

Derek Lee, representative for the MMA, concedes that in the U.S., Yaskawa America Inc., Waukegan, Ill., is the major sponsor of Mechatrolink. “However, in China, the major sponsor is actually a CNC company enthusiastic about promoting the Mechatrolink network,” Lee says. Why the big push? The network's same-cycle data resends boost noise immunity, which is particularly critical in CNC applications, where data cannot be missed.

“Mechatrolink is the only motion field network that utilizes a ‘data retry’ feature,” explains Lee. “This feature allows a resend of data to a slave when the slave does not acknowledge receipt of data — and the resend occurs within the same transmission cycle as the original data.” Other networks supporting data retry resend that data in the next transmission cycle. “This is why Mechatrolink does not support the Ethernet communication technology, beyond a physical RJ-45 option to utilize the physical aspect of Ethernet,” says Lee.

Mechatrolink also supports motion commands that allow positioning from an input within the same command — instead of reading the position from the controller, then having the controller issue the new position command.

On the physical level, Mechatrolink supports the standard single-point RJ-45 connector that competing networks support, plus an industrial miniature connector sporting dual-point contacts and a 360° shield — versus the two-point shield connection on an RJ-45.

Interestingly, even major sponsors of common protocols make concessions and integrate other networks: The A1000 variable speed drive from the Drives & Motion Division of Yaskawa America, for example, includes connectivity for Mechatrolink-II — expansion ports for additional I/O, and feedback — in addition to network communications including DeviceNet, EtherNet/IP, Modbus TCP/IP, Profibus-DP, and PROFINET. Embedded application functions, such as PID control, droop control, and function block programming provide system level control without a standalone controller.

In a similar way, the decentralized IndraDrive Mi servo drive from Bosch Rexroth, Hoffman Estates, Ill., also allows a host of Ethernet components to connect via a multi-Ethernet interface. The latter reduces the configuration of SERCOS III, PROFINET IO (RT), EtherNet/IP, and EtherCAT communication protocols to simple software adjustments.

Optional modules of the past meant installing separate control cabinets or panels throughout a machine, but “decentralized I/O modules and drive controllers can only reach their full cost reduction potential and effectiveness if they completely rid themselves of these additional distribution panels,” explains Abdulilah Alzayyat, product manager at Bosch Rexroth, Hoffman Estates, Ill. “This reduces overall costs as well as the space needed by the devices.”

By using the Rexroth IndraDrive Mi, machine builders can offer multiple designs without having to change the size of the main cabinet. By enabling additional Ethernet and peripheral devices to be connected directly to the drive, these components no longer need to be wired into the control cabinet.

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As an original contributor to the development of SERCOS, Bosch Rexroth still emphasizes that particular communications network — for motion control and I/O: “IndraDrive Mi has the drive and its intelligence integrated directly on the motor, allowing additional Sercos III and peripheral devices to be connected directly to the IndraDrive Mi,” explains Alzayyat.

For example, for one module requiring Sercos III fieldline I/O for a specific application, decentralized Sercos III I/O can be directly connected, thanks to a combination of hardware, firmware, and communication protocol available.

“This reduces the use of DIN-rails in the cabinet because the Sercos III fieldline I/O is mounted on the machine module and not in the cabinet,” says Alzayyat.

That said, traditional cabinets are increasingly modular in their own right, to dramatically simplify setup and reduce cost. DIN rails take the lead here: Electrical installations for industrial control were quite complicated before the widespread adoption of this standard. Now, the elegantly simple standardization on DIN rail geometry allows for organizing compatible terminal blocks, power supplies, motor starters, relays, circuit breakers, I/O, and contactors inside control cabinets into tidy rows — by simply snapping into the rails.

Established by the Deutsche Institute von Normen (DIN), this German Institute of Standards ensures dimensional uniformity so that the rails accept the mounting of all the compatible electrical products mentioned. The most common DIN rail is 35 mm in length (TS35 or DIN 46277-2) and 7.5 to 15 mm thick. Designers can choose products standardized to DIN rail dimensions from any number of manufacturers — to save time and space, while centralizing electrical contacts. In fact, dc and ac power supplies, terminal blocks, Ethernet switches, and discrete power relays abound for DIN setups.

According to Christian Kastinger, key account manager at B&R Industrial Automation Corp., Roswell, Ga., truly modular assemblies (such as the B&R setup shown on this page) require four things: Fine granularity of automation components and cabinetless designs — and in communication, one bus for everything, plus versatile topologies.

“Until recent years, the limiting factor in modular motion-system design was often the structure of the electrical system — with power distribution, control, and drive technology in a centrally located control cabinet,” adds Markus Sandhöfner of B&R. Why? “Electrical and electronic equipment and its connections for all possible option combinations vary, so the control cabinet and cabling could only be completed after the entire machine was assembled. In contrast, modularization of mechanical connections for future expansions is (for the most part) implemented rather easily.”

Now, however, electrical and electronic equipment design is increasingly flexible. A basic requirement for this type of modular structure is the ability to connect all types of different control and automation hardware anywhere via the system bus. Here, “B&R relies on the Ethernet-based Powerlink fieldbus,” reports Sandhöfner. “It allows all combinations of bus, ring, or star topologies to be implemented, which makes it easier to move system components away from the centralized control cabinet. The control cabinets are then always identically equipped and can be small while meeting the needs of the main machine.”

Powerlink also allows easy pathways to other fieldbuses — to simplify connection to purchased modules that use their own fieldbus interface.

Hardware modularity abounds here, too: “Even the spectrum of electric motor functions is represented,” concludes Sandhöfner, “from frequency inverter controlled three-phase asynchronous drives and synchronous drives for servo, torque or linear motors to highly precise stepper motor control with integrated feedback.”

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