Explore the essentials of capacitive tactile force sensing - its unique advantages, challenges, and real-world applications - and see how SingleTact sets a new standard in a crowded market.
What is a Capacitive Tactile Sensor?
A capacitive tactile sensor is a sensor technology that is used to detect changes in capacitance caused by direct contact from touch, pressure, or force applied to the sensing face.
They typically consist of at least two metal electrodes and a compressible dielectric material. When pressure is applied to the sensor sensing face from physical contact with the sensor, the distance between the metal plate electrodes changes, altering the capacitance, which is then measured by a dedicated capacitance sensor/meter and translated into meaningful data by an electronic device.
The sensing range can be easily controlled by altering the dielectric constant between the two plates and/or the geometry of the sensor sensing face during the sensor design phase. This means a tactile capacitive sensor is applicable in a wide range of applications, from feather touch to heavy industrial.
Unlocking Precision:
Exploring Capacitive Tactile Force Sensing Technology
The capacitive sensor's outputs can be either digital or analogue, but it is common that the sensor will have a digital output for simple integration and analysis in customer applications. This also makes the sensor output wires robust to interference.
How are they different from capacitive proximity sensors?
These are not the same as other capacitive technologies such as capacitive sensing touch screens, or capacitive proximity sensors that are used to detect the capacitance change caused by proximity to an external capacitive object.
The subtle difference is that the capacitive proximity sensor and capacitive sensing touch screens typically uses the self capacitance mode, whereas capacitive tactile sensors typically use mutual capacitance mode between the two plates.
A tactile capacitive sensor, as a result of using mutual capacitance mode is generally well shielded to avoid the effect of stray capacitance and electrical field on the output signal, and so is an excellent option for EMI/EMC noisy applications, unlike a capacitive proximity sensor.
Advantages of Tactile Capacitive Sensors
A tactile capacitive sensor offers several valuable advantages for force/pressure sensing:
1. High Precision on any media:
The tactile capacitive sensor excels in precision, offering the ability to detect even the subtlest changes in touch or pressure exerted by solid or liquid targets, or even gasses, with the appropriate sensor.
2. Immune to external EM fields:
The tactile capacitive sensor shielding makes them largely immune to most EM interference on their sensing surface including: electrostatic field discharge (ESD), electrical field, magnetic field, and proximity effects.
3. Excellent EMC characteristics:
The tactile capacitive sensor is electrically quiet, allowing use in strict EMC environments. Despite often utilising a high frequency oscillator circuit to make the sensor work, tactile capacitive sensors emit only a minimal electrical field, unlike a typical resistive sensor or inductive sensor due to their excellent shielding on the sensing surface.
4. Wide Dynamic Ranges Addressed
A tactile capacitive sensor can be made to fit most practical dynamic range requirements, by making subtle adjustments to the dielectric constant or sensing surface area during manufacture. From feather touch to heavy industrial loads, there is a capacitive tactile sensor for you.
5. Simple Setup
A SingleTact capacitive sensor requires minimal setup, with dedicated electronics for easy setup with a computer system, plus an excellent API to integrate your sensor with low level systems in OEM applications.
6. Robustly Flexible
A tactile capacitive sensor can be very flexible, capable of dynamic flex operating cycles, unless required to be rigid of course. The sensing end of flexible sensors can conform to complex geometries, providing truly representative pressure and load responses.
Disadvantages of a Tactile Capacitive Sensor
Despite their many benefits, a tactile capacitive sensor can also have some limitations:
1. Sensitivity to Environmental Change:
A tactile capacitive sensor is sensitive to environmental effects such as temperature and humidity (unless it is a waterproof sensor). This is a sensitivity shared with capacitive proximity sensors amongst others as they alter the capacitive sensor geometry and dielectric constant respectively. A tactile capacitive sensor should be used at a relatively constant temperature unless taring, calibration, or algorithmic compensation is used to control the error.
2. Limited Sensing Range:
Tactile capacitive sensors do not have an adjustable sensing range, as they are typically set up to give the best precision over their nominal working range. Their nominal working range is predominantly positive with limited ability to handle negative loads, which can cause physical damage to the sensing surface.
3. Cost:
Due to the complexity of the electronics required to read capacitive sensors, and the multiple layers giving them the best EMC performance, they do come at a higher cost than other technologies such as resistive or strain gauge sensors, but at a significantly lower cost than equivalent piezo based systems.
Capacitive Tactile Sensor Pros and Cons Summary
Capacitive tactile sensors offer excellent benefits compared to competing technologies, boasting high precision in contact with solids, liquids, and gasses, a sleek low profile, and superb EMC characteristics making them ideal for complex and demanding sensing environments.
These benefits do come at the cost of... well, cost, compared to other budget sensing options. Care must be taken with these types of sensors to mitigate environmental errors sources and limit the range of negative loads they are subjected to.
Examples of Tactile Capacitive Sensing Applications
Capacitive sensing finds application in various industries and products, including:
1. Consumer Electronics:
Capacitive Buttons and Controls: Capacitive sensors are also used to create touch-sensitive buttons and controls on electronic devices, to replace mechanical buttons and switches.
These touch-sensitive controls offer a sleek and modern design while providing tactile feedback and intuitive operation for functions such as volume control, power on/off, and menu navigation, whilst also giving force proportional responsiveness not available in traditional capacitive buttons. This is beneficial as it only responds to load, rather than being sensitive to any electrical property of the body.
2. Automotive and Aerospace:
In the automotive industry, capacitive sensing technology is increasingly being integrated into vehicle design to enhance cost-effectiveness in design, convenience, and safety. Some notable applications include:
Aerodynamic Measurement: Capacitive sensors are also employed in touch-sensitive climate control systems, allowing drivers and passengers to adjust temperature, fan speed, and airflow direction with simple gestures.
3. Medical Devices:
In the field of healthcare, capacitive sensing technology plays a crucial role in various medical devices and applications, facilitating accurate measurements, monitoring, and diagnostics. Some key applications include:
Medical Imaging: Arrays of tactile sensors are routinely used to measure tissue hardness variation, a known differential for diseases such as breast cancer.
Pressure Sensing: Capacitive pressure sensors are used in medical devices such as blood pressure monitors, respiratory therapy equipment, and infusion pumps to measure pressure and provide real-time feedback.
4. Industrial Automation:
Capacitive sensing technology plays a vital role in industrial automation applications, providing precise and reliable force and touch sensing capabilities for robotics, manufacturing equipment, and human-machine interfaces. Some notable applications include:
Industrial Spray Sensing: In this application, sensors with a low pressure sensing range are used as liquid targets for spray tests. When properly waterproofed, a tactile sensor can be used to detect liquids as well as solid materials in contact with the sensor's body. This type of sensor can easily detect solid or liquid levels, and unlike other capacitive liquid level sensors, can be used with conductive materials.
Robotic Grippers and End Effectors: Capacitive sensors are integrated into robotic grippers and end effectors to enable precise force control and object detection during grasping, manipulation, and assembly tasks. Capacitive sensing allows robots to adjust their grip force and position based on the properties and condition of the objects being handled, ensuring accurate and efficient operation in industrial environments.
Industrial Process Control: A tactile capacitive sensor can be used in process control in industrial settings, either as binary input devices to a process controller providing a positive signal or negative signal based on a load threshold or a continuous sensor output for characterising process compliance. A sensor incorporated in a glove or fingertip device can ensure production systems are electrically connected at the cable connection end, and mechanical limit switches are within load tolerance as examples.
5. Ergonomic Design
Tactile capacitive sensors, with their flexibility and immunity to external capacitance and EMI are excellent options for use in ergonomic design.
Capable of conforming to complex geometry, and available in customisable form factors, tactile capacitive sensors provide accurate and interpretable results in a wide range of human body interactions such as the hand, and head, as shown. These can be used to assess safety standards, design comfortable consumer products, as well as medical and ergonomic research.
SingleTact: Setting a New Standard
SingleTact distinguishes itself in the tactile sensing market with its innovative approach and advanced features:
SingleTact Pros:
Ultra-Thin Design: SingleTact sensors boast an ultra-thin profile of 0.3mm, making them suitable for applications with tight space constraints.
High Sensitivity: SingleTact sensors offer exceptional sensitivity, enabling precise force measurement across the sensor’s sensing range even in delicate applications.
Customization Options: SingleTact provides customization options to tailor sensors with a manufacturer adjustable sensing range according to specific application requirements, ensuring optimal performance for your sensing range.
Integration Flexibility: SingleTact sensors can be seamlessly integrated into existing systems and devices, facilitating easy adoption. All this without the need for a single adjustment screw.
Rapid Setup and Visualisation: SingleTact USB sensor outputs directly to a PC and dedicated app, whilst the standard electronics are intended to connect to an arduino board, or similar microcontroller, providing both a convenient power supply and output to a serial monitor. The SingleTact USB features an indicator light on the printed circuit board, where the sensor's indicator light turns on proportionally to the applied force on the sensor.
Simple Data Synchronisation: SingleTact standard electronics features an interrupt output for data synchronisation in embedded systems.
SingleTact Cons:
Cost: SingleTact sensors may have a higher initial cost compared to some budget alternatives, which could be a consideration for budget-conscious projects.
Complexity: Integrating SingleTact sensors into complex systems may require specialized knowledge and expertise. SingleTact supports this with simple yet informative documentation available on our website.
Not waterproof: SingleTacts are sensitive to moisture, and so care must be taken to seal them in applications requiring liquid or reactive gas contact.
Summary
In conclusion, capacitive force sensing technology offers a compelling blend of precision, reliability, and versatility, making it an indispensable and valuable tool across various industries and applications. With SingleTact's cutting-edge solutions pushing the boundaries of what's possible, the future of capacitive pressure sensing looks brighter than ever.