Robot specification for nutraceutical processing.
Described as existing somewhere between the food and pharmaceutical industries, the emerging nutraceuticals sector is seemingly bound to adopt much the same robotic technology, in the interests of flexible manufacturing, shorter time-to-market and contamination-control requirements. With global nutraceutical sales set to reach $75 billion in 2007, maintaining market competitiveness, increasing throughput and enhancing product quality will doubtless be among the main motivations for investing in robotics, especially as many newly established manufacturing operations will not be shackled by legacy fixed automation. Moreover, smaller installation footprints, more complex working envelopes and substantially reduced hardware costs mean robots are extremely viable for SMEs and smaller production lines.
As with food and beverages and pharmaceuticals, nutraceutical applications will additionally benefit from removing human involvement from many processing and packaging tasks, in the interests of health and safety, hygiene and contamination control, with the added bonus that robots can be placed in harsh and restricted environments, as well as confined clean rooms. Products such as vitamins and supplements, probiotics, energy drinks, fortified cereals, functional foods and other processed nutraceuticals also suggest similar scope for flexible automation, in areas such as picking, packing and palletizing, incoming materials inspection, metering and filling, machine tending, clean room production and the like, all performed with a level of accuracy, repeatability and uptime that human operators cannot hope to equal, day in and day out.
Identifying the potential applications for industrial robots within your own production process is one thing; however, choosing the right machine for the task and integrating it into a fully functioning, safety guarded, automated work cell is quite another. That's the job of specialist, independent robot system integrators like my own firm, Barr & Paatz, and I thought it might be instructive to review the steps we ourselves take when specifying and building a robot installation. Of course, we employ sophisticated CAD/CAM software, 3D modelling tools and project management programs when developing automation solutions for customers, but the basic procedures are relatively straightforward.
First step is to consider the specific application and ascertain the type of work piece or component manipulation required, in order to determine the geometry of the robot. For more routine assembly, packaging, palletising or pick and place duties, we would opt for a 4-axis or SCARA (Selective Compliant Assembly Robot Arm) robot, which has two rotary joints at the 'shoulder' and 'elbow,' a linear joint that provides the vertical positioning, and a simple wrist joint. They are generally faster and offer a good price/performance ratio, but have a more restricted, quasicylindrical work envelope and less functionality than a 6-axis robot (see Figure 1).
As the name implies, the 6-axis or Articulate robot has six joints or 'degrees of freedom' (DOF) to control the location and orientation of the end-of-arm tooling, closely resembling the action of the human arm and wrist. With a larger, almost-spherical operating envelope and the capacity to reach over and around obstructions or twist and tilt the part, the 6-axis robot is the solution for complex processing and machine tending tasks.
At this point, it's worth mentioning in passing the 5-axis robot, which has a similar articulate geometry, but without the rotating wrist joint; this actually offers little more functionality than a SCARA and, given the price differential, means that we rarely specify a 5-axis machine. Similarly, a conventional 3-axis Cartesian or Gantry robot has linear motion in only three directions, requires a large volume in which to operate and lacks the versatility of true flexible automation. Again, in most cases, a 4-axis robot will do the same job better at a comparable price, whilst having the flexibility for redeploying onto secondary robotic applications, unlike the fixed geometry of a Cartesian type.
For nutraceutical picking and packaging applications, where high speed execution is likely to be critical, we should additionally consider Delta-type robots, with their parallel kinematics and servo motors mounted off the arms, on the overhead chassis. Typically resembling a three-legged spider, with a fourth moving element extending from the centre to manipulate the end-effector, they offer up to three translational and one rotational degree of freedom and, thanks to their low mass arms, can perform up to 130 picks per minute, compared with, for example, 60-65 ppm for a SCARA type.
Specifications for industrial robots focus on the number of axes, load capacity, reach and the X, Y and Z-axes travel, as well as repeatability. So having determined whether it's 4-axis or 6-axis geometry, we consider how heavy is the work piece/component and any associated tooling, such as a gripper or vacuum, how much distance has to be covered in the process and to how many different places within the operating envelope. This identifies how long the robot arm has to be, or reach, and the nominal and maximum load capacities. Then it's a question of identifying which manufacturer offers suitable candidate machines.
The choice of robot manufacturer usually depends on price/performance. Although, if the customer has previous experience with particular equipment and/or existing installations, that can also be an important factor. After 16 years in the automation industry, we have refined our choice down to three class-leading makes that cover most applications: namely Mitsubishi, Staubli including former Bosch Rexroth models, and Comau. With more than 30,000 installations worldwide, Mitsubishi is a market leader in small-scale robots, with SCARA models handling payloads up to 15 kg and articulated-arm machines up to 12 kg. Staubli mainly covers the middle of our range, extending up to 130 kg, including former Bosch Rexroth SCARA models, and its excellent 24 hr field service means this brand is ideal for critical manufacturing environments. Although covering most ranges, we consider Comau's main strength in our product portfolio to be handling heavier payloads in a compact footprint, including the world's most powerful robot capable of lifting 800 kg.
For Delta 2/3 robots, we are excited about the potential of PWR's Unigrabber series, especially designed for high-speed tasks. The range extends from the UG2, with a 30 kg payload and 2 DOF for medium weight pick and place tasks, through to the ultrafast UG-D4 for single-picking and top-loading applications, which features a 1000 g payload, 3 or 4 DOF, a large working envelope and speeds up to 130 cycles/min.
Further options, where available, include floor, wall or ceiling mounting, to allow for any space constraints and optimize manoeuvrability, additional electronic protection to IP67 and special versions for clean room or food-grade applications. As we shall see later, end-of-arm connections for electrical and pneumatic peripherals and the means for internally mounting cables are further considerations.
So far so good and you can perform the robot selection stage interactively yourself, on our own website at www.barr-paatz.co.uk. Next is the configuration and specification of the gripper or end-effector, also known as end-of-arm tooling (EOAT). This is a key area of robot system design, as the precision and repeatability of any robotic process depends on how the EOAT grips, holds, locates, lifts and releases parts or products. The most commonly used tooling is the gripper, which activates jaws or fingers to manipulate parts, mainly pneumatically but also electrically or hydraulically. The weight and dimensions of the work piece, its shape, the specific process and permissible opening/closing times will determine factors such as two or more fingers, spring-assisted action, friction coefficient and gripping force, although it should be remembered that acceleration imposed on the work piece by the speed of movement should also be taken into account. Different jaw materials and facings, including thermoplastics and cushioning, accommodate work pieces liable to marking or damage as do those with, say, knurling or serrations.
For flat or moulded sheet materials like plastics, metal, glass, wood, cardboard and paper, vacuum cups offer the best solution for work piece handling and there are numerous permutations of cup material, profile and abrasion/ heat- resistance to accommodate a range of surfaces. Magnetic and electromagnetic pickups provide further options if parts have a ferrous content and, ideally, a large flat contact surface. Whatever the EOAT employed, it is critical that the combined weight of the tooling, the gripped component and ancillaries such as vacuum generators do not exceed the machine's payload capacity or create an unacceptable increase in cycle times, which is where our spreadsheet calculations come into play. Normally, any associated cable and hose is channelled internally through the robot arm, with plug-in connections at the base, but sometimes external routing of lines and ducting is unavoidable and must be configured into the design calculations.
Guarding and Transport
Sometimes overlooked in initial specifying, yet absolutely critical from a safety legislation angle, are working area guards or protective barriers. Robots are virtually silent and extremely fast in operation, so safety devices are needed to bar access to a potential source of danger and offer protection against the possibility of objects or liquids flying off the machine. For larger robot cells, we employ Bosch Rexroth's EcoSafe modular protection fence system, which allows us to comply with EN safety standards, exceeds minimum height requirements and cannot be removed without tools, even using force. For smaller cells, we integrate the guarding into the system, employing Rexroth's MGE modular aluminium profile system, stainless steel panels and shatter- resistant heavy duty polycarbonate viewing windows. In both instances, mechanical and electrical interlocks and magnetically locked access doors prevent working parts from operating while a hazardous zone is being accessed.
If operators do require regular access to the work cell, and where pallets or conveyors routinely pass through apertures in the guard barriers, an opto electronic device will maintain safety integrity without constantly interrupting the robot cycle. Here, we tend to use Sick light barriers, light curtains and light grids for finger, hand and personnel protection; these use contact-free optical sender and receiver units and help make work processes safer, without inhibiting production.
In this context, I should also refer to material infeed/outfeed transport mechanisms, which have to be integrated into the guarded robot cell and are largely dictated by the weight and dimensions of the product itself, as well as required throughput speeds. We rely on conveyors, vibratory feeders, powered rollers and other transfer systems from the likes of Rexroth and Interroll who, when necessary, can produce customized pallets and tooling to carry workpieces at the required orientation and frequency. In this context, we sometimes install 'machine vision' systems from market leaders Cognex, using cameras positioned over the conveyor belt or production line to analyse the shape of objects and determine whether they are in the correct orientation for pick and place processes; similarly, we are exploiting the potential of PWR's Pinpoint robot vision guidance for high speed picking applications, as well as detecting and removing downgraded products from fast-moving conveyor lines.
HMI and Simulation
Human input, in the form of operator commands, diagnostics and programming changes, is incorporated into the robot cell by means of an HMI (human machine interface). We favour the class-leading Pro-face touchscreen graphic operator interfaces, which help make complex processes easier to understand and simpler to control, helping to eliminate user error. Multilayered protocols enable varying levels of access to software commands, from routine machine operation, through maintenance to reprogramming, at the same time providing inbuilt connectivity with robot controllers and plant wide networks. Touchscreen controls are also clean and user-friendly, leaving mechanical push buttons for simple functions such as guard resets.
Finally, to prove the system, optimize the work cell layout and verify the reachability of all positions, we run the proposed configuration on our in-house COSIMIR 3D robot simulation package. This means that not only the robot action, but also its interaction with grippers and transport mechanisms are realistically simulated; all I/0 electrical connections can also be mapped out and the tested programs downloaded directly into the robot controller. This process also reassures you, the customer, that the work cell will perform the functions it's supposed to, at the throughput speeds required. It only remains for us to actually source the components and build the system, which is quite another story.
If all this sounds complex, then it is. However, a specialist robot system integrator like ourselves has all the multidisciplinary skills and in-house software tools to perform these calculations and design functions cost-efficiently, as well as familiarity with and practical experience of all the hardware options, so it really does pay to involve us at the earliest possible stage.
For more information
Barr & Paatz
7-11 Paragon Units, Ford Road
Totnes Industrial Estate, Totnes
TQ9 5LQ, UK.
T. +44 1803 869 833
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|Publication:||Nutraceutical Business & Technology|
|Date:||Sep 1, 2007|
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