5 Replies Latest reply on Oct 11, 2020 11:33 PM by AH_96

    Capsense vs Magsense for a tactile sensor

    JeSi_4326976

      Hi,
      I am trying to look at the differences between Capsense and Magsense for a robotic gripper tactile sensor.
      I am mainly curious about magsense's ability to read any object applying pressure (light to high) on the sensor, and its possible resolution and sensing speed compared to capsense. I am easily able to get a frequency of a few hundred Hz with capsense readings, with a matrix of 5x5 elements.

       

      1. Is it possible to use some sort of compressible overlay with magsense that would help capture the presence of any object? It could be a conductive fabric or something, and the object would compress it to change inductance?
      I am currently trying to implement this with capsense, but a finger is always generating a much stronger signal than any other object compressing the overlay.

       

      2. Is magsense advantageous for fast reading and small sensor elements for a high sensing resolution?

       

      Thanks!

        • 1. Re: Capsense vs Magsense for a tactile sensor
          AH_96

          Hello JeSi_4326976

           

          1. Is it possible to use some sort of compressible overlay with magsense that would help capture the presence of any object? It could be a conductive fabric or something, and the object would compress it to change inductance?
          I am currently trying to implement this with capsense, but a finger is always generating a much stronger signal than any other object compressing the overlay.

          Yes, MagSense is made for these applications specifically. With CapSense, the higher signal is due to the additional capacitance added by finger capacitance, whereas with MagSense, the finger will not modify the inductance and therefore, will not cause any signal change. Over the sensor, a metallic plane must be kept. In our kits, this is achieved by using a 0.5 mm thick Aluminium.

           

          Whenever any material touches the Al sheet, the pressure causes the Al overlay to flex and this changes the inductance of the coil, thereby increasing the signal.

           

          2. Is magsense advantageous for fast reading and small sensor elements for a high sensing resolution?

          Yes. MagSense scan speed is comparable with that of CapSense. The scan speed is the number of subconversions divided by the Lx clock frequency, which will be in the order of micro seconds (note that this is subject to the coil design which affects the Lx clock frequency). The resolution depends on a lot of factors such as the thickness of the metal plate, the separation between sensor and the metal overlay, the material of the overlay etc.

           

          Best regards,

          Hari

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          • 2. Re: Capsense vs Magsense for a tactile sensor
            JeSi_4326976

            Hi Hari,
            This is wonderful news.

            AH_96 wrote:

             

            The resolution depends on a lot of factors such as the thickness of the metal plate, the separation between sensor and the metal overlay, the material of the overlay etc.

             

            We currently have a 4x7 button matrix on a 5cm x 3cm PCB with capsense, which gives a good sensing capability and resolution with a doped overlay.

             

            I assume you cannot make an official statement about magsense maximum touch resolution, but can you affirm if yes or know it would be able to reach something similar as this, or it would be well under our current settings with capsense?

             

            Here is a photo of the resolution we can get with our capsense sensor PCB, holding a cup by the handle:
            Do you think mapping the force applied on a magsense sensor would be possible this way?

            • 3. Re: Capsense vs Magsense for a tactile sensor
              AH_96

              Hi JeSi_4326976

               

              The output map looks like a touchpad response. Note that with MagSense you will not be able to design a touchpad configuration. You can have a matrix button arrangement and the limitation is that the spacing between the coils must be 0.5* Dout, where Dout is the outer diameter of the coil.

              So the response might not be uniform and the sensors will work as individual buttons. If the application is that of matrix button, then this can be used and will enable 'Any-Sense'.


              Best regards,

              Hari

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              • 4. Re: Capsense vs Magsense for a tactile sensor
                JeSi_4326976
                The output map looks like a touchpad response. Note that with MagSense you will not be able to design a touchpad configuration. You can have a matrix button arrangement and the limitation is that the spacing between the coils must be 0.5* Dout, where Dout is the outer diameter of the coil.
                Sorry my statement was misleading. The current PCB is made of (4x7) 28 individual CSD buttons. I am looking for an optimal replacement to confer better resolution, reading speed and feasibility between other capsense widgets and magsense (magsense which I barely know by now). A matrix, if it cannot get rid of ghost touches, would not be a viable option since we are trying to develop something similar to robotic sensory skin. The maximum amount of widgets for a magsense block is 16, correct?

                 


                So the response might not be uniform and the sensors will work as individual buttons. If the application is that of matrix button, then this can be used and will enable 'Any-Sense'.


                Best regards,

                Hari

                What is any-sense? I wasn't able to find an answer online.

                 

                From what I see, magsense doesnt seem to be very good resolution-wise, even though it would have helped quite a lot with the even sensing of any object. Either we consider using 2 PSoCs (with one magsense block each), or we remove the possibility of working with magsense for this project and focus on capsense

                • 5. Re: Capsense vs Magsense for a tactile sensor
                  AH_96

                  Hi JeSi_4326976

                   

                  Sorry my statement was misleading. The current PCB is made of (4x7) 28 individual CSD buttons. I am looking for an optimal replacement to confer better resolution, reading speed and feasibility between other capsense widgets and magsense (magsense which I barely know by now). A matrix, if it cannot get rid of ghost touches, would not be a viable option since we are trying to develop something similar to robotic sensory skin. The maximum amount of widgets for a magsense block is 16, correct?

                  That is correct. Only 16 sensors are supported. So I'm afraid a 4x7 arrangement would not be possible. A CSX matrix would be able to get rid of ghost touches, but it is sensitive only to grounded objects.

                   

                  What is any-sense? I wasn't able to find an answer online.

                  What I meant is that, with a metal overlay, it would be able to sense anything that can apply a pressure on it. The necessity of grounded objects is not present with MagSense.

                   

                  From what I see, magsense doesnt seem to be very good resolution-wise, even though it would have helped quite a lot with the even sensing of any object. Either we consider using 2 PSoCs (with one magsense block each), or we remove the possibility of working with magsense for this project and focus on capsense

                  The choice of MagSense vs CapSense depends solely on the application. With CapSense, the object to be detected must be grounded. Whereas, with MagSense, this limitation is not present. Any pressure on the metallic overlay, causing a change in distance between the overlay and the sensor can be detected. This is true for any object such as gloves. To have an idea of the resolution, you can take a look at the performance of the CY8CKIT-148, which is our inductive sensing eval kit.

                   

                  Best regards,
                  Hari

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