At a Glance:
Internet of Things (IoT) devices and apps are providing consumers with improved access to and control of their digital life. Common examples include residential smart systems like thermostats, appliances and garage door openers—each of which can be viewed and operated via a mobile device.
Naturally, those operating commercial facilities and industrial manufacturing sites would like to experience some of the same IoT benefits as personal consumers. There is a lot of useful data at these locations and these site operators could benefit from remote visibility into equipment status and alarms. Industry users are already familiar with traditional automation products which could offer some level of connectivity, but these products could be costly and difficult to design, implement and maintain.
In recent years, a collection of hardware, software and methods termed as the Industrial IoT (IIoT) has improved upon this situation. Industrial end-users will find it is now simpler and less expensive to establish remote connectivity using the IIoT by taking advantage of basic and workable solutions to make valuable information widely available.
Traditional industrial automation platforms have included specialized and robust programmable logic controllers (PLCs) and human-machine interfaces (HMIs) connected using various networking and fieldbus communication methods. Larger combinations of PLCs and HMIs may be called supervisory control and data acquisition (SCADA) systems. These elements were designed to deliver around-the-clock reliability and on-site visibility, but easy and secure integration and communication were much less of a consideration.
The situation has improved, first as industrial wired Ethernet media and protocols became practical for industrial use, and next as Wi-Fi gained sufficient performance to work well for industrial applications.
Today, many industrial protocols have matured or been developed over the past few years to work well for on-site automation system communications such as EtherNet/IP, Modbus TCP and OPC UA. However, these have been less well suited to deliver a good IIoT experience for IT, cloud and mobile networking systems.
Don Pham, senior product marketing manager, at IDEC Corporation.
Conventional automation products and protocols typically require a rigorous configuration and hierarchy to move data from a field sensor, to a field controller, to a site network, to a PC data server and then to the cloud. The resulting multi-layered architecture means these types of implementations can be complicated and expensive to create and manage.
To economically make industrial data available for all types of remote and mobile end-user access, a newer protocol and methodology was needed to meet the goals listed below, some of which may appear to be at odds with traditional computer networking requirements:
The protocol which has risen to prominence for addressing these issues is MQTT, which provides many features to meet the needs of IIoT users by compressing the architecture into just three roles (Fig. 1):
1. MQTT simplifies industrial data handling architectures, enabling MQTT-capable field IoT field devices like PLCs to publish and subscribe data directly through a broker.IDEC
Industrial automation devices which include MQTT capability are the latest answer for efficiently, economically and securely integrating commercial and industrial automation with the cloud using IIoT principles. These may be field devices which simply publish data, or more complex devices like PLCs which need to publish and subscribe to data.
While the network traffic associated with typical business computing is relatively large, this differs for industrial data packets which are most often small, and may change frequently or be very intermittent. MQTT is suitable for these types of small data payloads and consumes little communication message overhead; it is optimized to communicate (and use bandwidth) only as needed.
Most traditional industrial protocols follow a “poll and response” structure, where users must carefully arrange the source and destination, and also assign a polling rate which executes whether data is changing or not.
MQTT has improved the situation with a “publish and subscribe” or “pub/sub” model. For pub/sub, data producers publish data to a broker as the data becomes available. Subscribers notify the broker of what data they want, and the broker sends updated data to existing subscribers when it changes, or the latest available data to new subscribers.
Instead of predefining large data communications blocks, users instead configure “topics” to manage data “payloads.” A topic is constructed as a layered structure, which helps users organize the data in a logical and easy-to-understand manner (Fig. 2).
2. Users define easy-to-understand topics within MQTT as layered structures to manage and organize data payloads; a sample topic could be “site/area_1/temperature.”IDEC
Because IIoT devices connected using MQTT may be installed using less reliable network connections found in remote locations, an important feature of the protocol is how subscribers are notified if source data becomes unavailable. This “last will and testament” feature enables a subscriber to detect a disconnected publisher, so users can configure the system to act accordingly.
New subscribers can be added at any time, and each will immediately connect and receive the latest data and topic status. Both subscribers and publishers can dynamically be added or removed at will.
Another important aspect of industrial communications is security. Traditional industrial protocol implementations like Modbus TCP and EtherNet/IP simply allowed devices to connect and access each other using IP addresses. Once upon a time this was satisfactory, especially when such systems were air-gapped from the rest of the world.
For today’s highly-networked IIoT systems, MQTT is the protocol of choice. It relies on proven IT-based security measures. All communications are initiated by publishers in an outbound manner, which is allowed by most IT firewalls (and allows the firewall to protected against inbound threats). Centralized MQTT brokers ensure that only properly authenticated publishers can connect.
All these features are becoming available in certain automation products. Some users will have targeted applications and may be reluctant to commit to complex automation platforms which offer MQTT. In some cases, MQTT-capable micro PLCs are becoming available so users can economically apply them and begin realizing value (Fig. 3).
3. Some micro PLCs, like the IDEC FC6A shown here, now incorporate the MQTT protocol so users can economically take advantage of IIoT connectivity.IDEC
After selecting MQTT-capable devices and PLCs, there is still some legwork to be done by users to establish the broker. The broker can be created using an on-site computer, or more typically established in the cloud via an internet connection. For simplicity and best overall connectivity, many users with internet connectivity will prefer cloud-based solutions. There are three approaches:
Technical users will find the full scratch option is the most work, but gives proficient end-users the most control and could yield long-term savings. For this method, a user would typically create their own cloud service based on a commercial cloud platform like Amazon Web Services (AWS), Google Cloud Platform (GCP) or Microsoft Azure. That means they need to develop:
The easiest approach for many users would be to subscribe to a SCADA/dashboard cloud service which already includes the above listed functions and is hosted on the virtual servers of a cloud platform. Once the broker is established, MQTT devices can immediately publish and subscribe to the broker, and users can configure associated applications for viewing and reporting the data (Fig. 4).
4. Most users will find it easiest to use a SCADA/Dashboard cloud service for connecting MQTT-capable field device data and PLCs for remote monitoring and reporting.IDEC
A third option in the middle of the previous two is for users to buy the IoT SCADA/dashboard software and to instantiate it on a local or cloud-based server. The resulting functionality can be much like the cloud service, but this option gives the user more control and perhaps some cost savings.
Typical consumers are familiar with mobile apps which let them interact with many types of devices and systems. Commercial and industrial end-users are looking for similar advantages. As these users begin incorporating IIoT methods to securely gain remote access to their assets, they will find MQTT-capable devices and micro PLCs are available to help them. Modern IIoT products and features are much simpler, easier to implement and less expensive than traditional SCADA methods.
Don Pham is the senior product marketing manager at IDEC Corporation and has more than 15 years of detailed experience with industrial automation products, including PLCs, HMI touchscreens, machine safety and sensors.
By submitting this form and personal information, you understand and agree that the information provided here will be processed, stored and used to provide you with the requested services in accordance with Endeavor Business Media’s Terms of Service and Privacy Policy.
As part of our services, you agree to receive magazines, e-newsletters and other communication about related offerings from Endeavor Business Media, its brands, affiliates and/or third-party partners consistent with Endeavor’s Privacy Policy. Contact us at [email protected] or by mail to Endeavor Business Media, LLC, 331 54th Avenue N., Nashville, TN 37209.
You can unsubscribe from our communications at any time by emailing [email protected].
The right mechanical torque limiter protects equipment and prevents robots from running into each other.
Engineers working at robotic companies, auto makers, automatic equipment manufacturers and in many other industries all commonly use torque overload protection devices, slip clutches or torque limiters. They design in limiters to prevent accidental collisions between robots and other moving machines, to avoid overloads on production and assembly machines, and to keep drives and speed reducers safe. All of these collisions or overloads lead to machine downtime, along with the associated higher maintenance costs and lower productivity.
This Rencol tolerance ring uses spring force and friction as its operating principle but is not an actual Friction Type torque limiter. It gets installed coaxially into a drive instead of being installed in series with an assembly. It surface waves provide a radial force which acts as the spring force to create friction between components.
There are two types of torque overload protection: mechanical and electrical. This article focuses on mechanical protection. That’s because mechanical torque limiters are quicker at providing overload protection than electrical versions. In some cases, protection is supplied within milliseconds of the torque overload by mechanical limiters. Electrical limiters require sensors and other electrical devices to detect and monitor torque overloads. And finally, mechanical limiters are much less costly and simpler to install and use.
Mechanical torque limiters, which provide slip clutch functionality, fall in one of four types: friction, shear pin, ball or roller release detent. There are also pneumatic and hydraulic type torque limiters.
Friction type torque limiter.
Friction type. This type of torque limiter uses spring loaded friction disks that act on one another, similar to an automobile clutch. Adjusting the spring-force preload on the disks determines the limiter’s torque slip threshold. Under normal torque load conditions, the limiter transmits the entire amount of torque. If the torque exceeds the threshold, the friction disks slip against each other to bleed off or eliminate some of the torque. This type of torque limiter lowers the torque almost immediately when a higher level of torque is applied.
Shear pin type torque limiter.
Shear-pin type. In these torque limiters, metal shear pins connect two rotating bodies and a constant shear force is applied to these shear pins when torque is transmitted. Under normal torque loads, these limiters let it all be transmitted. When there’s an overload, the shear pins break and all torque transmission stops. The shear pins must be replaced after an overload. It is also difficult to accurately control the level of torque at which the shear pin will reliably and consistently break.
Ball and detent type torque limiter.
Ball or roller release detent type. In one of these limiters, a series of balls or rollers in one rotating body are matched with mating sockets or detents in the other rotating body. The balls or rollers are spring loaded to remain in their mating sockets or detents. Under normal torque loads, the limiter transmits all of it. In an overload, the centrifugal force on the balls or rollers overcome the spring forces and they disengage with their mating sockets or detents, preventing any torque from being transmitted until the torque drops and the balls are recaptured by the sockets or detents.
Pneumatic and hydraulic type. These limiters use pneumatic or hydraulic pressure to put force on the elements transmitting torque. These torque limiters tend to be complex and expensive and are not frequently used unless there is a special or compelling reason to do so.
The main criterion for specifying a torque limiter is the torque value threshold at which the limiter should slip or disengage. This value can be determined by the following equation:
T = [HP × (5,252/RPM)] / 0.73756
Where:
T = Torque (Newton-meters).
HP = Motor’s horsepower.
RPM = Revolutions per minute at the location where the torque limiter would be located in the system.
Here is an example: If you have a motor rated at 2 HP and there is a 1,800 RPM rotational speed where the torque limiter would be located, the torque is calculated as follows: Torque (in N-m) = [2 × (5,252/1,800)] / 0.73756 = 7.91 N-m.
And if ft-lb is the unit for torque, convert N-m to ft-lb by the following formula: Ft-lb = N-m × 0.73756 (or N-m = ft-lb/0.73756).
For electric motors, horsepower can be calculated from the motor’s torque and speed ratings. For example, if the motor is rated for 2,000 RPM and 4 N-m of torque, horsepower is calculated as follows:
Horsepower = (4 × 0.73756) / (5,252 / 2,000) = 1.123
Motors are also commonly rated in watts. The conversion from watts to horsepower is: 745.7 Watts = 1 HP, or 1 W = (1/745.7) HP
Engineers can also apply a safety factor to create a safety margin for the drive motor. Keep in mind that a safety factor is different from a motor’s Service Factor.
NEMA Standard MG 1-2014 defines a Service Factor as: “A multiplier which, when applied to rated power, indicates a permissible power loading that may be carried under conditions specified for the service factor.” NEMA’s definition of Service Factor also contains the phrase “normal service conditions.” These conditions include rated voltage and frequency at a maximum temperature of 40°C (104°F) and a maximum altitude of 3,300 ft (1,000 m). Only under these conditions can the motor handle the full Service Factor overload. NEMA also warns that even if the motor can perform successfully at ±10% of the rated voltage, operating it at other than the rated voltages may affect motor performance. The decision to apply a safety factor, if any, is solely the responsibility of the end-user.
The torque limiter should have a torque threshold that lets it slip only at torques higher than those the motor generates when first beginning to move. No one wants unnecessary and nuisance slipping when a machine or robot starts up, as this creates unnecessary and costly downtime.
Another consideration is the amount of space available for the torque limiting device. Depending on the application, there will be varying degrees of space available and design flexibility for adding a torque limiter. The torque limiter should be between the speed reduction unit ( a gearbox, harmonic drive, gear reduction unit or other speed reduction component) and whatever is being driven. This lets it protect both the motor and speed reduction device.
Another consideration is the reset style of the limiter. Do you want to require human intervention for resetting it? Although this adds downtime, some engineers might want this option. If this is the case, then a shear pin limiter might be the best choice as it always needs human intervention to restart. However, if you want to automatically or immediately re-start, a friction type or a ball or roller detent type would do the trick.
By doing calculations to determine the torque value threshold at which the limiter should slip or disengage, designers and engineers can determine the torque limiter’s torque-slip capacity. And depending on considerations such as available space, system design flexibility and reset method, they can also determine which torque limiter type would be best suited for a robot or production machine.
Kenneth Smith is market development manager for Saint-Gobain, Bearings Strategic Business Unit.
By submitting this form and personal information, you understand and agree that the information provided here will be processed, stored and used to provide you with the requested services in accordance with Endeavor Business Media’s Terms of Service and Privacy Policy.
As part of our services, you agree to receive magazines, e-newsletters and other communication about related offerings from Endeavor Business Media, its brands, affiliates and/or third-party partners consistent with Endeavor’s Privacy Policy. Contact us at [email protected] or by mail to Endeavor Business Media, LLC, 331 54th Avenue N., Nashville, TN 37209.
You can unsubscribe from our communications at any time by emailing [email protected].