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Power & Force Limiting Cobots for Dull, Dirty and Dangerous Applications

Collaborative robots, or cobots, is currently one of the most exciting topics in automation. But what do people mean when they say “collaborative robot”? Generally, they are talking about robots which can safely work near and together with humans. The goal of a collaborative robot system is to optimize the use of humans and robots, building on the capabilities of each.

There are four modes of robot collaborative operation defined by the global standard ISO/TS 15066. We discussed these modes in a previous blog, Robot Collaborative Operation.

This post will go more deeply into the most commonly used mode: power & force limiting. Robots in this category include ones made by Universal Robots, as well as FANUC’s green robots and ABB’s Yumi.

What is power & force limiting?

Power & force limiting robots are designed with limited power and force, along with physical features to avoid or reduce injury or damage in case of contact. These robots are generally smaller, slower and less powerful than traditional robots but also more flexible and able to work near or with humans — assuming a risk assessment determines it is safe to do so.

The standards define the creation of a shared or collaborative work space for the robot and human, and define how they may interact in this space. In a power & force limiting application, the robot and operator can be in the shared/collaborative work space at the same time and there may be contact or collision between the operator and the collaborative robot system (which includes the robot, gripper/tool and work piece). Under the proper conditions the features built into the power & force limiting robot allow this close interaction and contact to occur without danger to the operator.

What technologies allow these robots to work closely with humans?

The limiting of the robot’s force can be implemented in several ways. Internal torque/feedback sensors in the joints, external sensors or “skins” and/or elastic joints are some of the methods robot suppliers use to assure low force or low impact. They also design possible contact areas to avoid injury or damage by using rounded edges, padding, large surface areas, etc. to soften contact. Grippers, tools and work pieces also need to be considered and designed to avoid injury or damage to people and equipment.

Peripherally, additional sensors in the robots, grippers, tools, work holders and surrounding work stations are critical parts of high performance robot applications. Connecting these sensors through protocols such as IO-Link and PROFISafe Over IO-Link allows more tightly integrated, better performing, and safer collaborative robot systems.

Where are power & force limiting robots typically applied?

Similar to traditional robots, power & force limiting robots are best applied in applications which are dull, dirty and/or dangerous (the 3 Ds of robotics). They are especially well suited to applications where the danger is ergonomic — repetitive tasks which cause strain on an operator. In many cases, power & force limiting robots are being applied to cooperate closely with people: the robots take on the repetitive tasks, while the humans take on the tasks which require more cognitive skills.

A large number of the customers for power & force limiting robots are small or medium-sized enterprises which can not afford the investment and time to implement a traditional robot, but find that power & force limiting robots fit within their budget and technical capabilities.

What are some of the benefits and drawbacks to power & force limiting robots?

Benefits:

  • Low cost
  • Fast, simple programming and set up; often does not require special knowledge or training
  • Small and lightweight
  • Easy to deploy and redeploy
  • Can be fenceless
  • Low power usage
  • Close human-robot interaction

Drawbacks:

  • Slow
  • Small payload
  • Low force
  • Low precision (not always the case, and improving)

Final Thoughts

Buying a power & force limiting robot does not necessarily mean that fences or other safeguards can be removed; a risk assessment must be completed in order to ensure the application is appropriately safeguarded. The benefits, however, can be significant, especially for smaller firms with limited resources. These firms will find that power & force limiting robots are very good at cost-effectively solving many of their dull, dirty and dangerous applications.

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The Emergence of Device-level Safety Communications in Manufacturing

Manufacturing is rapidly changing, driven by trends such as low volume/high mix, shorter lifecycles, changing labor dynamics and other global factors. One way industry is responding to these trends is by changing the way humans and machines safely work together, enabled by updated standards and new technologies including safety communications.

In the past, safety systems utilized hard-wired connections, often resulting in long cable runs, large wire bundles, difficult troubleshooting and inflexible designs. The more recent shift to safety networks addresses these issues and allows fast, secure and reliable communications between the various components in a safety control system. Another benefit of these communications systems is that they are key elements in implementing the Industrial Internet of Things (IIoT) and Industry 4.0 solutions.

Within a typical factory, there are three or more communications levels, including an Enterprise level (Ethernet), a Control level (Ethernet based industrial protocol) and a Device/sensor level (various technologies). The popularity of control and device level industrial communications for standard control systems has led to strong demand for similar safety communications solutions.

Safety architectures based on the most popular control level protocols are now common and often reside on the same physical media, thereby simplifying wiring and control schemes. The table, below, includes a list of the most common safety control level protocols with their Ethernet-based industrial “parent” protocols and the governing organizations:

Ethernet Based Safety Protocol Ethernet Based Control Protocol Governing Organization
CIP Safety Ethernet IP Open DeviceNet Vendor Association (ODVA)
PROFISafe PROFINET PROFIBUS and PROFINET International (PI)
Fail Safe over EtherCAT (FSoE) EtherCAT EtherCAT Technology Group
CC-Link IE Safety CC-Link IE CC-Link Partner Association
openSAFETY Ethernet POWERLINK Ethernet POWERLINK Standardization Group (EPSG)

 

These Ethernet-based safety protocols are high speed, can carry fairly large amounts of information and are excellent for exchanging data between higher level devices such as safety PLCs, drives, CNCs, HMIs, motion controllers, remote safety I/O and advanced safety devices. Ethernet is familiar to most customers, and these protocols are open and supported by many vendors and device suppliers – customers can create systems utilizing products from multiple suppliers. One drawback, however, is that devices compatible with one protocol are not compatible with other protocols, requiring vendors to offer multiple communication connection options for their devices. Other drawbacks include the high cost to connect, the need to use one IP address per connected device and strong influence by a single supplier over some protocols.

Device level safety protocols are fairly new and less common, and realize many of the same benefits as the Ethernet-based safety protocols while addressing some of the drawbacks. As with Ethernet protocols, a wide variety of safety devices can be connected (often from a range of suppliers), wiring and troubleshooting are simplified, and more data can be gathered than with hard wiring. The disadvantages are that they are usually slower, carry much less data and cover shorter distances than Ethernet protocols. On the other hand, device connections are physically smaller, much less expensive and do not use up IP addresses, allowing the integration into small, low cost devices including E-stops, safety switches, inductive safety sensors and simple safety light curtains.

Device level Safety Protocol Device level Standard Protocol Open or Proprietary Governing Organization
Safety Over IO-Link/IO-Link Safety* IO-Link Semi-open/Open Balluff/IO-Link Consortium
AS-Interface Safety at Work (ASISafe) AS-Interface (AS-I) Open AS-International
Flexi Loop Proprietary Sick GmbH
GuardLink Proprietary Rockwell Automation

* Safety Over IO-Link is the first implementation of safety and IO-Link. The specification for IO-Link Safety was released recently and devices are not yet available.

The awareness of, and the need for, device level safety communications will increase with the desire to more tightly integrate safety and standard sensors into control systems. This will be driven by the need to:

  • Reduce and simplify wiring
  • Add flexibility to scale up, down or change solutions
  • Improve troubleshooting
  • Mix of best-in-class components from a variety of suppliers to optimize solutions
  • Gather and distribute IIoT data upwards to higher level systems

Many users are realizing that neither an Ethernet-based safety protocol, nor a device level safety protocol can meet all their needs, especially if they are trying to implement a cost-effective, comprehensive safety solution which can also support their IIoT needs. This is where a safety communications master (or bridge) comes in – it can connect a device level safety protocol to a control level safety protocol, allowing low cost sensor connection and data gathering at the device level, and transmission of this data to the higher-level communications and control system.

An example of this architecture is Safety Over IO-Link on PROFISafe/PROFINET. Devices such as safety light curtains, E-stops and safety switches are connected to a “Safety Hub” which has implemented the Safety Over IO-Link protocol. This hub communicates via a “black channel” over a PROFINET/IO-Link Master to a PROFISafe PLC. The safety device connections are very simple and inexpensive (off the shelf cables & standard M12 connectors), and the more expensive (and more capable) Ethernet (PROFINET/PROFISafe) connections are only made where they are needed: at the masters, PLCs and other control level devices. And an added benefit is that standard and safety sensors can both connect through the PROFINET/IO-Link Master, simplifying the device level architecture.

Safety

Combining device level and control level protocols helps users optimize their safety communications solutions, balancing cost, data and speed requirements, and allows IIoT data to be gathered and distributed upwards to control and MES systems.

 

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Connecting Safety Devices to a Safety Hub

Safety device users face a dilemma when selecting safety components: They want to create a high-performance system, using best-in-class parts, but this often means buying from multiple suppliers. Connecting these devices to the safety control system to create an integrated system can be complicated and may require different cabling/wiring configurations, communications interfaces and/or long, hardwired cables.

Device-Level Protocols

One solution, discussed in a previous blog on industrial safety protocols, is to connect devices to an open, device-level protocol such as Safety Over IO-Link or AS-i Safety At Work. These protocols offer a simple way to connect devices from various suppliers using non-proprietary technologies. Both Safety Over IO-Link and AS-i Safe offer modules to which many third party devices can be connected.

Connecting to a Safety HubSafety-Arch_012518

The simplest way to connect to a safety hub/module is to buy compatible products from the hub supplier. Many safety block/hub suppliers also offer products such as E-stops, safety light curtains, door switches, inductive safety sensors and guard locking switches which may provide plug & plug solutions. There are, however, also many third party devices which can also be easily connected to some of these hubs. Hubs which are AIDA (Automation Initiative of German Domestic Automobile manufacturers) compliant allow connection of devices which are compatible with this standard. Generally, these devices have M12 connectors with 4, 5 or 8 pins, and the power, signal and ground pins are defined in the AIDA specifications. Most major safety device manufacturers offer at least one variant of their main products lines, which are AIDA pin-compatible.

AIDA/Safety Hub Compatible Devices

Some suppliers have lists of devices which meet the M12 pin/connector AIDA specification and may be connected to AIDA compatible modules. Note that not all the listed safety devices may have been tested with the safety blocks/hubs, but their specifications match the requirements. AIDA compatible devices have been identified from all major safety suppliers including Balluff, Rockwell, Sick, Schmersal, Banner, Euchner and Omron STI; and range from safety light curtains to door switches to E-stop devices.

Easy Connection

While some manufacturers prefer to focus on locking customers into a single supplier solution, many users want to combine devices from multiple suppliers in a best-in-class solution. Selecting a safety I/O block or hub which supports AIDA compatible devices makes it fast and easy to connect a wide range of these devices to create the safety system that is the best solution for your application.

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Industrial Safety Protocols

There are typically three or more communication levels in the modern factory which consist of:

  • Enterprise level (Ethernet)
  • Control level (Ethernet based industrial protocol)
  • Device/sensor level (various technologies)

IO-Link

The widespread use of control and device level communications for standard (non-safety) industrial applications led to a desire for similar communications for safety. We now have safety versions of the most popular industrial control level protocols, these make it possible to have safety and standard communications on the same physical media (with the appropriate safety hardware implemented for connectivity and control). In a similar manner, device level safety protocols are emerging to allow standard and safety communications over the same media. Safety Over IO-Link and AS-i Safety At Work are two examples.

This table lists the most common safety control level protocols with their Ethernet-based industrial “parent” protocols and the governing organizations:

chart1

And this table lists some of the emerging, more well-known, safety device level protocols with their related standard protocols and the governing or leading organizations:

Chart2
* Safety Over IO-Link is the first implementation of safety and IO-Link. The specification for IO-Link Safety was released recently and devices are not yet available.

Ethernet-based safety protocols are capable of high speed and high data transmission, they are ideal for exchanging data between higher level devices such as safety PLCs, drives, CNCs, HMIs, motion controllers, remote safety I/O and advanced safety devices. Device level protocol connections are physically smaller, much less expensive and do not use up IP addresses, but they also carry less data and cover shorter distances than Ethernet based protocols. They are ideal for connecting small, low cost devices such as E-stops, safety switches and simple safety light curtains.

As with standard protocols, neither a control level safety protocol, nor a device level safety protocol can meet all needs, therefore cost/performance considerations drive a “multi-level” communications approach for safety. This means a combined solution may be the best fit for many safety and standard communications applications.

A multi-level approach has many advantages for customers seeking a cost-effective, comprehensive safety and standard control and device solution which can also support their IIoT needs. Users can optimize their safety communications solutions, balancing cost, data and speed requirements.

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What Exactly is Safety Over IO-Link?

Users of IO-Link have long been in search of a solution for implementing the demands for functional safety using IO-Link. As a first step, the only possibility was to turn the actuators off using a separate power supply (Port class “B”, Pins 2, 5), which powers down the entire module. Today there is a better answer: Safety hub with IO-Link!

Automation Pyramid.png

This integrated safety concept is the logical continuation of the IO-Link philosophy. It is the only globally available technology to build on the proven IO-Link standards and profisafe. This means it uses the essential IO-Link benefits such as simple data transport and information exchange, high flexibility and universal applicability for safety signals as well. Safety over IO-Link combines automation and safety and represents efficient safety concepts in one system. Best of all, the functionality of the overall system remains unchanged. Safety is provided nearly as an add-on.

In the center of this safety concept is the new safety hub, which is connected to an available port on an IO-Link master. The safety components are connected to it using M12 standard cable. The safety profisafe signals are then tunneled to the controller through an IO-Link master. This has the advantage of allowing existing infrastructure to still be used without any changes. Parameters are configured centrally through the user interface of the controller.

Safety Hub

The safety hub has four 2-channel safe inputs for collecting safety signals, two safe outputs for turning off safety actuators, and two multi-channel ports for connecting things like safety interlocks which require both input and output signals to be processed simultaneously. The system is TÜV- and PNO-certified and can be used up to PLe/SIL 3. Safety components from all manufacturers can be connected to the safe I/O module.

Like IO-Link in general, Safety over IO-Link is characterized by simple system construction, time-and cost-saving wiring using M12 connectors, reduction in control cabinet volume and leaner system concepts. Virtually any network topology can be simply scaled with Safety over IO-Link, whereby the relative share of automation and safety can be varied as desired. Safety over IO-Link also means unlimited flexibility. Thanks to varying port configuration and simple configuration systems, it can be changed even at the last minute. All of this helps reduce costs. Additional savings come from the simple duplication of (PLC-) projects, prewiring of machine segments and short downtimes made possible by ease of component replacement.

Capture

To learn more about Safety over IO-Link, visit www.balluff.com.

 

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Safety Over IO-Link Helps Enable Human-Robot Collaboration

Safety Over IO-Link makes it easier to align a robot’s restricted and safeguarded spaces, simplifies creation of more dynamic safety zones and allows creation of “layers” of sensors around a robot work area.

For the past several years, “collaboration” has been a hot topic in robotics.  The idea is that humans and robots can work closely together, in a safe and productive manner.  Changes in technology and standards have created the environment for this close cooperation. These standards call out four collaborative modes of operation: Power & Force Limiting, Hand Guiding, Safety Rated Monitored Stop, and Speed & Separation Monitoring (these are defined in ISO/TS 15066).

Power & Force Limiting

Power & Force Limiting is what many people refer to when speaking about Collaborative Robots, and it applies to robots such as Baxter from Rethink Robotics and the UR series made by Universal Robots.  While the growth in this segment has been fast, there are projections that traditional robots will continue to make up 2/3 of the market through 2025, which means that many users will want to improve their traditional robot solutions to “collaborate”.

Hand Guiding

Hand guiding is the least commonly applied mode, it is used for very specific applications such as power assist (one example is loading spare tires into a new car). It generally requires special equipment mounted on the robot to facilitate the guiding function.

Safety Rated Monitored Stop and Speed & Separation Monitoring

Safety Rated Monitored Stop and Speed & Separation Monitoring are especially interesting for traditional robots, and require safety sensors and controls to be implemented.  Customers wanting closer human-robot collaboration using traditional robots will need devices such as safety laser scanners, safety position sensors, safety PLCs and even safety networks – this is where Safety Over IO-Link can enable collaborative applications.

SAfety

Many of IO-Link’s well-known features also provide advantages for traditional robot builders and users:

1) Faster & cheaper integration/startup through reduction in cabling, standardized connectors/cables/sensors and device parameterization.

2) Better connection between sensors and controllers supports robot supplier implementation of IIoT and improved collaboration by making it easier to gather process, device and event data – this allows improved productivity/uptime, better troubleshooting, safer machines, preventative maintenance, etc.

3) Easier alignment of the robot’s restricted and safeguarded spaces, simplifying creation of more dynamic safety zones to support closer human-robot collaboration.

The third item is especially relevant in enabling collaborative operation of traditional robots.  The updated standards allow the creation of a “shared workspace” for the robot and human, and how they interact in this space depends on the collaborative mode.  At a simple level, Safety Rated Monitored Stop and Speed & Separation Monitoring require this “shared workspace” to be monitored, this is generally accomplished using a “restricted space” and a “safeguarded space.”  These “spaces” must be monitored using many sensors, both inside and outside the robot.

First, the robot’s “restricted space” is set up to limit the robot’s motion to a specific 3-dimensional volume.  In the past, this was set up through hard stops, limit switches or sensors, more recently the ANSI RIA R15.06 robot standard was updated to allow this to be done in software through safety-rated soft axis and space limiting.  Most robot suppliers offer a software tool such as “Safe Move” or Dual Check Safety” to allow the robot to monitor its own position and confirm it is where it is supposed to be.  This feature requires safe position feedback and many sensors built into the robot.  This space can change dynamically with the robot’s program, allowing more flexibility to safely move the robot and assure its location.

Second, a safeguarded space must be defined and monitored.  This is monitored using safety rated sensors to track the position of people and equipment around the robot and send stop (and in some cases warning) signals to the safety controller and robot.  Safety Over IO-Link helps connect and manage the safety devices, and quickly send their signals to the control system.

In the past, integrating a robot with safety meant wiring many safety sensors with long cable runs and many terminations back to a central cabinet.  This was a time consuming, labor intensive process with risk of miswiring or broken cables.  IO-Link significantly reduces the cost, speed and length of connections due to use of standard cables and connectors, and the network approach.  It is also much simpler for customers to change their layout using the network, master & hub approach.

Customers wanting collaborative capability in traditional robots will find that Safety Over IO-Link can significantly simplify and reduce the cost of the process of integrating the many advanced safety sensors into the application.

To learn more, visit www.balluff.com.