Robots in collaboration with humans

Collaborative robots in manufacturing

Andy Pye looks at the emerging technology of collaborative robotics and some of the safety implications which need to be addressed.

Traditionally, the automotive industry has led the way in using robots on a large scale to perform tasks of varying complexity. Elsewhere, British firms are lagging behind their overseas counterparts when it comes to robotics, and this is nowhere more true than in the food industry.

“It’s evolving very slowly in our experience, and that’s probably the same for our competitors,” says Fanuc regional sales manager John Rainer. He suggests that one reason might be the structure of the food chain in Britain and the behaviour of retailers: “In Scandinavia they’ll look at a five-year payback, but in the British food industry a supplier will only get a six-month contract from the supermarket, so how can they justify that sort of investment?”

But recently, there has been a noticeable uptake in robotics in the food processing sector. Robots are now taking on more light-touch and delicate duties. Improved vision and conveyor tracking, advanced gripping tools, washdown capabilities, and ease of integration mean that the latest generation of robots combine affordability, reliability and speed with the flexibility of quick product changeover.

The advancements in vision technology also address another regular concern expressed by food producers; that of replicating human quality checks. In reality, adding ‘sight’ to a robot can aid quality control. What’s more, packaging code reading capabilities can play a key role in meeting product traceability requirements, further enhancing quality control. Automated systems can also manage shape recognition and check that the right pack and the right label are married with the product itself, all set up in one system accessible via one interface.

Flexible, continuous production is essential in the face of evolving consumer preferences – new tastes are arising due to health consciousness and cost. We now have organic, gluten-free, sugar-free, low-fat, high-fibre, low-sodium and caffeine-free variants of many products; the desire of food firms and retailers to build brands through a broadening range of portion sizes and packaging formats (including fridge packs and club-store sizes) is also driving product diversification; and consumers are seeking smaller-quantity packs that meet low-budgets.

Omron cites improved control and integration as key factors driving the adoption of robotic systems. Following the acquisition of Adept Technologies, Omron now offers all three primary classes of robots, fully integrated into Omron’s Sysmac automation platform and programming environment. Meanwhile, Omron’s smaller, existing two lines of SCARA and Delta robots will continue to be offered alongside the new range. “Despite the Adept range being the larger of the two, the ranges are also complementary – for example, by providing a mini-Delta robotic system to complement the models in the Adept range. Also, while Omron’s existing SCARA robots can carry higher payloads, albeit at slower speeds, the more compact Adept systems provide expanded flexibility with regard to application compatibility” says Omron’s Marketing Manager Dan Rossek.

Amongst the brightest new stars in the Omron Adept Technologies range is the Quattro s650H Delta (or “parallel”) robot. Claimed to be the world’s fastest industrial robot, it is specifically designed for high-speed applications in packaging, manufacturing, assembly and material handling. It is the only parallel robot in the world that features a patented four-arm design (rather than the usual three), advanced control algorithms and a large working envelope.

Safety issues

Back in 1961 when General Motors introduced the first industrial robot to its production line, humans were at high risk inside a robot’s work zone. But as robots have become more refined, it has been easier to introduce more devices that could monitor a robot’s surroundings. Devices such as vision and force sensing were introduced so that the robots could see and feel what was around them.

In recent years we have seen the emergence of collaborative robots – or Cobots – that are easier to program and that can work alongside humans. In contrast to traditional robots, which cannot operate in an operator-occupied workspace without safety fencing, these cage-free robots can work side by side with humans on shared or separate tasks.

The term “collaborative robots” usually refers to power and force limited robots that are all equipped with force sensing. This means that in any situation they can feel an abnormal force and stop their motion immediately. Although they still cannot avoid a crash, they can reduce its impact and avoid certain types of incidents, like crushing accidents. This makes them safer for human-scaled operations, since they can work alongside humans and, in the case of an accident, will not severely injure anyone.

Collaborative robots are probably the easiest type of robot to integrate into a workshop. Doing so requires minimal programming knowledge, does not require additional safety devices and they can easily be fixed on a table.

Although collaborative robots are still relatively new, their applications are multiplying exponentially and more workshops are introducing them. Although safety requirements are not fixed yet, several countries with stringent safety regulations, such as Germany, have adopted collaborative robots in their production lines with excellent results.

However, Cobots do still present new safety concerns. There is a thin line between a safe and unsafe robot. According to Stewart Robinson, Principal Engineer and Functional Safety Expert at TÜV SÜD Product Service, the increased need for adequate protection of people from the safety risks associated with industrial robot systems led to the development of an international and European standard which has two parts.

* EN ISO 10218-1:2011 Robots and robotic devices – Safety requirements for industrial robots – Part 1: Robots
* EN ISO 10218-2:2011 Robots and robotic devices – Safety requirements for industrial robots – Part 2: Robot systems and integration.

While EN ISO 10218 already contains some guidance on the use of Cobots, it is widely acknowledged that this guidance needs to be enhanced. Consequently, a Technical Specification (ISO/TS 15066 Robots and robotic devices – Safety requirements for industrial robots – Collaborative operation) is currently in preparation.

In order to ensure that humans are not exposed to unacceptable risks when working collaboratively, the current standards describe four separate measures that can be used to provide risk reduction. It is required that at least one of these is fulfilled, in addition to having visual indication that the robot is in collaborative operation.

* SAFETY-RATED MONITORED STOP: this requires that when it is detected that a human has entered the collaborative workspace, the robot should be stopped.
* HAND GUIDING: the human can guide the robot at the end effector by hand. Additional requirements for safety include safe-limited speed monitoring, a local emergency stop and the use of an enabling device which is a three position device that has to be held in the centre position.
* SPEED AND SEPARATION MONITORING: the robot must maintain a specified separation distance from the human and operate at a pre-determined speed. This measure requires careful risk assessment and needs to take account of safety distances, which should include the consideration of approach speeds of parts of the human body as described in EN ISO 13855.
* POWER AND FORCE LIMITING BY INHERENT DESIGN OR CONTROL: the power and force of the robot actuators need to be monitored by safety-related control systems to ensure that they are within limits established by a risk assessment.

In all four of the measures described above, the safety-related control system that provides this functionality needs to meet either:

* The Safety Performance Level d (PLd), with Category 3 architecture (the identified level to which the safety related parts of a control system resist faults and their subsequent behaviour if a fault occurs) as outlined within the standard EN ISO 13849 or
* Safety Integrity Level 2 (SIL 2) with hardware fault tolerance (HFT) 1, as set out in EN [IEC] 62061.

Whilst most other collaborative robots are encased in a sensing cover that stops the robot when a human gets too close, Fanuc’s s collaborative robot ensures safety through the use of intelligent sensors, which automatically stop the robot if it touches a human operator. This means the CR-35iA can go closer to the jig and other peripherals when required.

Rainer comments: “In real world applications, if someone accidentally gets closer to the robot than they should, you don’t necessarily want it to stop automatically. Slowing down might be a more appropriate response: it helps to optimise productivity, but at the same time eliminates sudden stoppages at high speeds which could lead to vacuum-gripped parts being dropped due to the high inertia. Only when a human puts a hand through the SC300 safety sensor will the robot stop. This vision-based protective device uses image processing technology to detect the intrusion of objects through its detection window. The sensor is continuously looking for a reflected pattern from special reflective tape around the cell entry window. When an object of a certain resolution blocks the device’s view of the pattern, the safety function is activated.”

Importantly, the human-safe CR-35iA Cobot has a 35kg payload, opening up applications that have previously been off-limits for both traditional industrial robots and lighter duty collaborative robots. With health and safety regulations stipulating 25kg as the maximum load a human operator may handle, there is a real requirement for a robot to handle higher loads than this.

Levels of robot safety

The national bureau of standards defines three levels of safety sensor systems in robots:

* Level 1 — perimeter penetration detection.
* Level 2 — intruder detection inside the workcell
* Level 3 — intruder detection in the immediate vicinity of the robot.

Level 1 systems are intended to detect that an intruder has crossed the perimeter boundary of the workcell without regard to the location of the robot.

Level 2 systems are designed to detect the presence of an intruder in the region between the workcell boundary and the limit of the robot work volume.

Level 3 systems provide intruder detection inside the work volume of the robot.

There are common means of implementing a robot safety sensing system

* Pressure sensitive floor mats — area pads placed on the floor around the workcell that sense the weight of someone standing on the mat. These can be used for either level1 or level2 sensing systems.
* Light curtain — consists of light beams and photsensitive devices placed around the workcell that sense the presence of an intruder by an interruption of the light beam. Use of light curtains would be more appropriate as level1 systems.
* Proximity sensors located on the robot arm could be utilised as level 3 sensors.

The safety monitoring strategies that might be followed by the workcell controller would include the following schemes.

* Complete shutdown of the robot upon detection of an intruder.
* Activation of warning alarms.
* Reduction of the speed of the robot to safe level.
* Directing the robot to move its arm away from the intruder to avoid collision.
* Directing the robot to perform tasks away from the intruder.

Note: there is another safety monitoring technique called a “fail-safe hazard detector.” The concept of this detector is based on the recognition that some component or basic hazard sensor system might fail and that this failure might not be found out until some safety emergency occurred. The fail-safe hazard detector is designed to overcome this problem.

Types of robots

* Portal robots: portal robots are mounted robotic systems that span a cubic handling area by means of three linear axes. The actual robotic kinematics (the moving axes) are located above the mounting.

* Articulated robots: articulated robots are industrial robots with multiple interacting jointed arms that can be fitted with grippers or tools. Because these arms can move through three dimensions, articulated robots offer a high  degree of flexibility. Depending on how many axes they have, they can offer up to six degrees of freedom, which enables almost any combination of movement. A limitation of articulated robots is that they generally have a restricted range and load capacity.

* Scaras (selective compliance assembly robot arms): a particular form of articulated robots. They have a single articulated arm that can only move horizontally. They work in a similar way to  human arms and are often called ‘horizontal articulated arm robots’. Scaras work in series, with each arm connected to only one other.

* Delta robots: spider-like delta robots – a special form of parallel robot – typically have three to four articulated axes with stationary actuators. Because their actuators are located in the base, these kinds of robots have only a small inertia. This enables very high speeds and acceleration.

Andy Pye

Andy Pye

Andy Pye is a graduate of Cambridge University and has had a high profile career in the technical press as well as being a pioneer in web publishing.
Andy Pye

Latest News Stories by Andy Pye (see all)

About Andy Pye

Andy Pye is a graduate of Cambridge University and has had a high profile career in the technical press as well as being a pioneer in web publishing.

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