Custom Transfer System Adds Value by the Millisecond

Services and products from hydraulics, pneumatics, electrics, and linear technology were linked by Rexroth engineers to produce a custom engineering concept for Swiss company Mikron Machining Technology. “The fact that Rexroth offers coordinated components from pneumatic, hydraulic and electric drive technology right through to high speed control enabled us to select the most suitable characteristics for specific functions,” said Rolf Held, design manager, Mikron. The result was a machine tool that makes real added value out of milliseconds.

In a production environment, fractions of a second count and can accumulate to the extent that they affect cycle times. Automated transfer systems play a key role in many industries, particularly when metal parts must be processed using a number of different machining sequences. Suppliers to the automotive industry, for example, machine a number of items considerably more economically using intelligent transfer units. The machines pick up workpieces in clamping devices and transfer them automatically to the individual machining stations where they are drilled, milled, turned, chamfered or de-burred. Threads are cut and knurled profiles applied. Even peripheral processes such as installation operations or checks can be integrated into these transfer operations. With the transfer concept, all parts can be machined simultaneously.

The Multistep™ XT-200 is setting new standards for transfer systems – especially for the control speeds and the drives used for the various functions. The system makes precision manufacturing possible in non-stop operation. At the same time, the individual stations work practically hand in hand.

Extremely short chip-to-chip times ensure nearly continuous machining, and the system can even be used for high speed cutting. A key advantage is that it combines the productivity of a linear transfer machine with the flexible re-tooling capability of a machining center.

The concept is based on individual interlinked dual spindle modules, which can be used on a stand alone basis, or spread over up to four modules. Five interpolating CNC axes and up to 144 tools machine complex small and medium series parts on five and a half sides without remounting. If the parts are automatically re-mounted in-process, it is possible to machine six sides. The Multistep™ can be adapted to the production volume at any time. In addition, a loading and unloading station can assume the component feed function.

Without a break
While the main advantage of this machine is precision manufacturing almost without a break, further advantages come from the short chip-to-chip time of less than a second and the unusual dynamics. Accelerating the Rexroth CKK linear systems up to 1.4 g to 52 m per minute and spindles with speeds up to 40,000 rpm make for short machining cycles. This is where drive technology from Rexroth comes in: rodless pneumatic cylinders from the BRP Rexmover Series with a diameter of 50 mm and a stroke of 400 mm, as well as a linear axis Type CKK20-145 for strokes of up to 1,100 mm. The maximum force on this axis is around 72 kN in the direction of movement.

“At the end of the day it’s the number of milliseconds that we gain from a number of different points that is the decisive factor,” said Held.

In the standard version, the Multistep™ is fitted with a high-speed CNC Rexroth IndraMotion MTX. Up to 64 axes can be operated in twelve CNC channels independently of one another. The maximum extended version features 54 axes that are required to work in parallel. “Using any other approach would mean that we would need at least two controls and we would have to combine these with each other,” said Held.

The PLC can process 1,000 instructions in 60 ms. At the same time the CNC offers, when controlling eight axes, an interpolation cycle time of 1 ms maximum. The Rexroth IndraDrive servo drives have integrated safety functions for secure hold and safe movement. “Also of interest is the so-called feedback capability, with which the generator capacity of the motors is fed back into the network during the braking operation,” noted Held. Mikron uses the force of hydraulic components for clamping the direct drive B/C axes. The tool clamping mechanisms in the motor spindles that close by means of spring assemblies are opened hydraulically. Here the valve blocks are the same for all spindle variations.

When it comes to workpiece handling in the loading and unloading station as well as workpiece transfer, it is pneumatics that takes care of speed and safety. With the HF03-LG “light generation,” Mikron uses a light and compact variant of the HF valve series. It has a narrow valve width, yet can flow up to 700 standard liters. By using plastic plates, the weight can be reduced even further. The pneumatic and electric controls are located towards the front and arranged in one direction, thus offering increased installation potential, compactness and the possibility of adapting to the space available. By way of an alternative to the traditional multi-pole connection, a field bus connection is used.

From a single source
When it comes to compressed air treatment, Series AS2 maintenance units feature a modular structure. The individual air treatment processes are brought together in maintenance units made from high quality plastic. Filtering, closed-loop control, lubricating and draining – the configuration is geared to user requirements. With the patented oil-fill system, the oil is directly extracted from the storage tank by suction using a hose. This means that the maintenance unit is protected against fouling by oil.

The maintenance units for the pneumatics are located, like the hydraulic power unit and the master control, in a separate control cabinet. The cabinet also houses the central lubrication, power connection and the fire extinguishing system. This arrangement corresponds to the modular structure of the Multistep™ and, by ensuring simple and rapid access to central components, guarantees that the unit is maintenance friendly.

Bosch Rexroth Group
www.boschrexroth-us.com

Mechatronics: New answers call for new questions

By Richard Vaughn, Product Engineer
Bosch Rexroth Corporation–Project Management Dept.

In a short time, mechatronics has evolved into a universally accepted engineering concept. It integrates mechanics with electronics – and with engineering itself. The result is expanded technological capabilities and assembly-line successes like the Cartesian multi-axis robot. Because it enables more flexible automated production, users can precisely control parameters such as weight, speed, reach, and work envelope. That is why mechatronics can be the answer to a variety of design challenges.

Mechatronics enables the development of creative designs that extend the capabilities of existing robotics and controls to new levels.

But obtaining the right answers requires asking the right questions – from the very first stage of a design. A mechatronics approach is a 3-stage ongoing process:
—Design – configure the system to accomplish a specific task.
—Integration – determine how components work together.
—Implementation – achieve optimum value in daily operations, and prepare for future changes.

As an example, consider the parameters involved in an application such as pin insertion in automobile underbodies traveling on an assembly line. Proper design begins with the determination of mathematical factors such as payload, travel distance, desired speed, and axes size. Then there are questions of machine control, motor size to deliver proper speed and torque, and even the operator HMI. There is also the key question of how much it all will cost.

The design of a mechatronics system requires a multidisciplinary focus — to root out potential difficulties before they grow into time-consuming, costly and distracting problems.

Here are a few specific mechatronics challenges—and some tips for handling them.

Keep envelope restrictions in mind. Consider work envelope restrictions including walls, supports, and safety barriers to avoid physical interference. The difference between length of a module and length of stroke is also crucial, especially when selecting linear actuators. A rodless actuator’s “dead length” means the actuator’s stroke is shorter than the apparent length of the cylinder. The best approach is to use a 3D simulation, rather than reconfigure system elements later in the project.

Find a proper protocol. Approach the marriage of controls and drives from different sources cautiously – it can lead to problems, especially when using off-the-shelf protocols such as PROFIBUS, DeviceNet or Ethernet. Some off-the-shelf protocols, such as Bosch Rexroth’s IndraControl components, can communicate with many proprietary controllers, but this may not be true of all protocols. Problems may arise if a controller running DeviceNet is added to a platform running PROFIBUS. Similarly, if your plant runs Ethernet, you may not be able to “plug in” a component from any vendor. During the specification phase, you should ensure that compatible off-the-shelf control systems are available for expansion or reconfiguration.

Consider the implications of specifications. Specifications can have powerful, difficult-to-foresee implications for mechatronics. For example, a 480 V 3-phase motor may be ideal for a servo application, but not if your drive amplifier is only capable of 220 V – which may require retrofitting a transformer. A change from Class 1000 to Class 100 semiconductor production clean room conditions may require third party specification.

Build in cable management. Often, this is the last challenge addressed, leading to last-minute scrambles to avoid interference with motion and parts pickup. Rather, cable management for a gantry pick-and-place application should be one of the first factors considered. A program such as Bosch Rexroth’s camoLINE can offer predefined cable management and 3D modeling, letting you “drop in” components to ensure all components work cleanly together.

Cable management is an important and often overlooked consideration during mechatronic system design.

Find the right tool for the job. An application that requires complex interpolative motion, such as cutting or gluing circular seals on catalytic converters, requires an interpolative motion controller and device. Attempts to adapt point-to-point controllers for these applications can be time-intensive and deliver inadequate precision. The best approach is to determine the circular interpolation path and identify the needed controller performance; that in turn will guide the selection of drives, power requirements, I/O and other elements to achieve that performance.

Following some basic tips like these can help avoid common – and costly – problems like either over engineering and over sizing machines (resulting in heavy-duty capabilities that are rarely if ever used) or under sizing machines (not accounting for occasional increases in payload or run speed).

Either situation can unnecessarily increase automation costs, which might discourage implementation of mechatronics – another reason why asking detailed questions is essential.

Integration
Mechatronics is clearly a cross-disciplinary science, requiring expertise in mechanical and electrical engineering as well as electronics and computers. But few have a background in all these disciplines. Those with expertise in one particular area, such as electrical engineering, may end up doing on-the-job training in other aspects of mechatronics, or trying to learn how to incorporate components from an unfamiliar manufacturer.

One effective approach is to use the services of an integrator who specializes in mechatronics and is experienced in blending mechanics and electronics. Cross-disciplinary integrators are becoming more common as mechatronics applications expand, and the trend toward cross-disciplinary integration skill is consistent with the current industry focus on accomplishing more with fewer people.

Integration can act as a “force multiplier,” extending the capabilities of existing technology to create quantum leaps in production efficiency, reduced downtime, and cost savings. For example, an automotive production line can be made many times more productive by substituting different control commands for retooling, and an outboard support axis added to a 3-axis Cartesian robot creates a gantry device. Many similar solutions are possible for designers who adopt a multidisciplinary, full-system approach.

Use of 3D simulation during the design phase of the project can prevent the need for reconfiguring system elements later in the project.

After integration, the final step is implementation. But the final step should be well planned early in the process, or the result can be significant delays and added machine or production line costs. Avoid potential problems by clearly defining the roles and responsibilities of integrator and customer. This task can be a challenge in a process that blends a number of different engineering disciplines to create an integrated solution. The key is communication, right from the beginning — including detailed questions. For example, regarding system adjustments or changes, what is the responsibility of the integrator and what can be done by on-site personnel? The answers should be carefully documented to head off potential problems before they start. Of course, no one can foresee the future. But good implementation envisions the context in which a mechatronics system will operate.

Cross-disciplinary integrators are becoming more common as mechatronics applications expand.

As a cross-disciplinary process, mechatronics demands integrated thinking to go with integrated engineering. Part of this thinking involves the ability to envision the day-to-day operation of assembly line functions, including the working environment and the blending of electronic protocols, to anticipate and head off potential disciplines. Be prepared for the reality of cross-disciplinary requirements that may call for an integration specialist to get all the components working together. Finally, to implement the system, clearly communicate with everyone involved about their roles and responsibilities. For mechatronics to be truly successful, the development process must involve not only mechanical and electronic elements, but process elements as well: the key phases of design, integration, and implementation.

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Software tools speed integration

Proper design begins with determining mathematical factors such as payload, travel distance, desired speed, and sizing of axes. Bosch Rexroth developed “LOSTPED”—a multi-step analysis process to help designers gather information for specifications.

To help answer mechatronic questions, Bosch Rexroth developed “LOSTPED”—a multi-step analysis process for gathering information for specifications. LOSTPED stands for Load (the weight or force applied), Orientation (direction each axis is mounted), Speed (and acceleration), Travel (distance and range of motion), Precision (repeatability or positioning accuracy), Environment (operating conditions), and Duty cycle (duration the machine will run; example: 24 hr/day, 5 days per week). In an automotive assembly application, for example, duty cycle and assembly line speed are crucial to determine insertion arm size, motor size and logic control, along with many other key factors.

Bosch Rexroth
www.boschrexroth-us.com