Technology, especially in robotics and industrial automation applications, continues to advance at a rapid pace. The demand for reliable and accurate sensing systems has grown commensurately. In this article, explore the portfolio of innovative solutions from Honeywell for pressure and force sensing.
Force Sensing
FMA force-sensing solutions from Honeywell are based on piezoresistive elements, which are superior to the existing style of physical switching mechanisms. This, coupled with calibration, temperature compensation, and direct mechanical coupling, provides stable accuracy over the life of the sensor. Additionally, a small package size makes these sensors able to be easily spec’d into the compact product designs that the market demands.
Pressure Sensing
The Amplified Basic Pressure (ABP) series of pressure sensors is useful for measuring the pressure of air or fluid lines. With a total-error-band measurement for accuracy, these sensors have all-inclusive measurement capabilities, including environmental considerations and other parameters. They’re also highly accurate, with an error rating of just ∓1.5% full-scale or ∓0.25% full-scale BFSL.
General Performance Characteristics
The digital outputs from these sensors allow for wireless transmission of data, which helps eliminate the need for bulky cable assemblies and wiring. With self-contained designs, they’re resistant to ingress by contaminants, so they can be used in almost any harsh-duty environment. From a life-cycle perspective, these sensors guarantee at least 1 million cycles.
As today’s technology in robotics increases in complexity and performance, there is a growing need for more reliable and accurate sensing systems. More systems today have closed-loop control than ever before, providing a tighter system response with more data-driven, error-free operation. And with a global pandemic that is still in effect, the use of robotics and full autonomy puts an even greater emphasis on reliability and efficiency for feedback systems. This article will explore Honeywell’s pressure and force solution portfolio for robotics applications, specifically when used for packaging or warehouse operation, and how it brings greater precision and reliability.
Honeywell’s sensors provide reliability and high accuracy
Traditionally, physical switching mechanisms have been used for feedback in motion-control platforms. One of the biggest shortcomings of these methodologies is long-term fatigue, which typically results in loss of accuracy/function over time.
Honeywell’s FMA force sensors (shown in Figure 1), which can be incorporated in robotic grippers used to help identify forces applied on items to ensure safe/accurate grasping, have been developed specifically to address this issue. Because of the piezoresistive elements, calibration, temperature compensation, and the direct mechanical coupling including tubing, membrane, or plunger, the FMA series of force sensors provides long-term, repeatable performance with a reliable mechanical interface. The fatigue does not impact its readings, which results in less downtime and higher productivity when compared with other similar sensors such as spring.
Figure 1: Honeywell FMA Force Sensor
Speaking of temperature compensation, the Amplified Basic Pressure (ABP) series of pressure sensors (normally used for measuring pressure of air or fluid in lines for control, power, or lubrication) provides a more comprehensive measurement of performance over its compensated temperature range. While most sensing platforms advertise accuracy specifications that do not include environmental considerations and other parameters, the ABP series includes a single specification for accuracy that is all-inclusive, called total error band (TEB). This specification is the worst error that the sensor could experience, which, for this series, is an industry-leading ±1.5% full-scale with ±0.25% full-scale best-fit straight line (BFSL). Figure 2 demonstrates the difference between BFSL and TEB while also showing the TEB over the total compensated pressure range. This fully characterized output and accuracy minimizes testing and calibration for each sensor and configuration, which, in turn, reduces manufacturing costs and improves system-to-system variability. It also allows for more flexibility of sensor interchangeability due to the minimal part-to-part variation.
Figure 2: Visual demonstration of accuracy for the ABP series of pressure sensors (left image compares BFSL with TEB and right image shows the TEB over the output range for an analog version)
While the ABP series supports board-level configurations, the Media Isolated Pressure (MIP) series of packaged pressure transducers (shown in Figure 3) offers heavy-duty measurements in a compact, stainless-steel, hermetically sealed construction. The sensor is meant for harsh environments with wide ranges and, like the ABP series, has an impressive TEB of up to ±0.75% full-scale with ±0.15% full-scale BFSL throughout a –40˚C to 125˚C temperature range. Because of its ruggedness, it can operate reliably in the presence of electromagnetic fields while also supporting almost any kind of liquid and gas media without the use of an internal seal. Its wide range of applications and operating environments includes industrial pumps, HVAC systems, hydraulics, transportation, and medical systems.
Figure 3: MIP series of pressure transducers
More advantages of FMA, ABP, and MIP series devices
While applications such as packaging robotics benefit greatly from improved reliability and accuracy, there are many other characteristics that should be considered as well.
The FMA micro force sensors, for instance, come in a very compact footprint (4.5 × 5 × 2.15 mm), which helps in space-constrained configurations like gripping assemblies. Also, their digital output (I2C or SPI) enables designers to incorporate wireless transmission to controllers, preventing the need for bulky cable assemblies and routing. In addition to wireless transmission, the digital interface also allows the sensor to be directly plugged into custom circuitry or interfaced to embedded processing without any major redesign needed. And diagnostic functions allow the user to determine if the sensor is working correctly by detecting internal shorts or opens, which greatly helps in resolving system errors and faults. The force sensor can withstand up to 3× its force range without any impact to its accuracy and repeatability (within the normal operating range).
ABP pressure sensors also provide a digital interface (24-bit I2C or SPI) that allows for flexible, custom connections as well as an IoT-ready interface. Also, the series offers a very wide range of pressure ranges and mechanical interfaces that support both dry gas and liquid media. This gives a variety of options, helping to design specifically for the range and accuracy requirements of the application. Additionally, its ultra-low power consumption (as low as 0.01-mW typical average power at 1-Hz measurement frequency) helps in power-constrained systems.
And MIP sensors can operate in almost any harsh duty environment, with notable features such as long-term stability, insulation resistance and dielectric strength, external freeze-thaw resistance, and excellent EMC performance. While providing a reliable option for the designer, they also provide great value. Multiple configuration possibilities provide flexibility of use in the application with no upfront NRE or tooling charges. And in critical applications, on-board diagnostics help to determine internal and external failure modes.
In addition to the features listed above, each of these series of sensors have an extensive lifespan with regard to cycling. The FMA and ABP sensors guarantee at least 1 million cycles, while the MIP devices can provide over 10 million pressure cycles.
Applications, examples, and reference material
For designers needing additional information and support on how to incorporate these sensors into an application, Honeywell provides documentation on installation, digital/analog interfaces, sensor selection, guidance on environmental variables, calibration and diagnostic functions/equations, pseudo-code snippets, and how to make use of many other features.
Figure 4, for instance, shows a flowchart for the ABP series of sensors on how to implement an auto-zero calibration routine with correction. This is taken from their technical note on auto-zero calibration. It also shows some real data describing the before and after of this routine for applications containing a large offset.
Figure 4: Auto-zero calibration routine for ABP pressure sensors and before (left)/after (right) comparisons
And for the FMA sensor, many technical documents exist to assist in both the electrical and mechanical integration process. The Microforce Sensor Coupling technical note describes how best to mechanically couple the sensor to the rest of your system, including notes on common coupling and mounting issues as well as examples and the equations to support them. Figure 5 shows a visual diagram of the optimal alignment of this sensor.
Figure 5: Diagram of optimal alignment for FMA force sensors
As with the ABP and FMA sensors, the MIP sensor also has many supporting documents to help easily integrate it into a custom configuration, such as application notes that describe how the MIP sensor can be used to provide continuous monitoring and feedback of system pressures (Figure 6). In the example below, the sensor reading is used to help control and regulate the flow of refrigerant while providing readings on the evaporator and compressor outlets.
Figure 6: HVAC implementation of MIP pressure sensor
To conclude, there is a growing need in the industrial automation industry for more reliable and higher-precision systems as production and operation become more dependent on robotics, especially with special circumstances such as a global pandemic. Reliability typically translates into longer-lasting, lower-maintenance systems, while higher accuracy generally allows for more efficient and robust operation. Honeywell’s pressure- and force-sensing platforms have been specifically developed to meet these needs, and many supporting documents can be referenced for design implementation from idea conception to mechanical integration. Check out how these sensing platforms can benefit your system design today.
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