12 Replies Latest reply on May 24, 2017 8:24 AM by rsc

    How to detect usage of height adjustable table?

    svendsen2032

      Hi at element14

       

       

      We have been trying to solve this matter for quite some time now, and we simply haven't been able to come up with a satisfying solution. We are working on a little "bot" placed on top of a height adjustable desk. The bot has to measure whether the desk is in a sitting or standing position. So we do either need to measure the movement and direction of movement or the height of the table. We have had some luck using proximity sensors (IR and US), but they are very dependent on the environment and placement, as e.g. a desk lamp can make the readings worthless.

       

       

      We are now working with an accelerometer and/or a barometric sensor, but the acceleration of a table is very small and the height difference of the table is only 20-40 cm's. So the sensors have to be very precise and sensitive.

       

       

      Soo, do you maybe have other ideas to what sensors we could use? Or maybe some insights into how we can get the accelerometer and barometric sensors to work properly? - would be a of great help

       

      Best regards Mads

        • Re: How to detect usage of height adjustable table?
          DAB

          Hi Mads,

           

          Have you considered using a capacitive sensor mounted to the desk?

           

          The TI sensor system can accurately detect objects up to about 50 cms.

           

          Another way would be to use a light and a camera to measure spot size, but now you are adding some complexity.

           

          Maybe an ultrasonic sensor?

           

          DAB

          1 of 1 people found this helpful
            • Re: How to detect usage of height adjustable table?
              svendsen2032

              I'm not sure I do fully understand. Do you suggest to use a capacitive sensor to measure the electrical field of the motors? Or, how do you figure it's possible to detect movement with a capicitive sensor?

               

              And a camera might be a bit too complex and we do experience users linking cameras to surveillance, which ain't good.

               

              We have been using ultrasonic sensors and they do work, however they are very dependent on the environment.

              1 of 1 people found this helpful
                • Re: How to detect usage of height adjustable table?
                  DAB

                  Should be easy.

                  Just lay down a conductive strip near the keyboard and connect it to the capacitive sensing circuit.

                  When the compute keyboard is on the desk, you get a good reading when the hands are on the keyboard.

                  If the keyboard is raised to a standing position, then the reading will be less and can probably provide you with a fairly precise distance from the desk top.

                   

                  A simple program can check the height every time the computer is in use, so you can record trend data over time.

                   

                  Clean, simple and automatic.

                   

                  DAB

              • Re: How to detect usage of height adjustable table?
                vandia

                On the note of what you're trying to do, you've giving detail of your method, but it still leaves your end goal rather vague.... especially with "acceleration of a table".

                It leaves the questions: "Is this to be done on multiple/different floorings under the table", "is the table moving", and "how frequently does the table change heights".

                 

                If you want to stick with the accelerators: I haven't used them before to know their accuracy, but I remember an Arduino SHARP library that averaged 5 IR scans into one value.... you could use 2 accelerators, one on each end of the table, and run each end through that same thing to alleviate some of the fluctuation.

                 

                IR has the highest fluctuation of any simple sensor I've used. It varies based on ambient light, and even EM waves. Sonar varies by texture of what it's to hit, which is why a question is the flooring. I also have an idea for determining if you're on carpet or hard flooring if you wanted it.

                1 of 1 people found this helpful
                  • Re: How to detect usage of height adjustable table?
                    svendsen2032

                    I'll try to be a bit more specific So we are trying to register everytime the users changes working position from sitting to standing and from standing to sitting. So our ultimate goal is to register every time the height adjustable table changes from a height between 65 to 85 cm to a height between 90 and 125 cm. A height adjustable table moves up and down with an average speed of between 18 mm/sek to 40 mm/sek. The table is used between 0 and 8 times a day (8 hours). The table can be placed in whatever office environment you can think of, so the room height is different, the floor material is different etc. Hope that helps a bit

                     

                    2 accelerometers might not be a bad idea. Think we will try and see if we can make it work.

                      • Re: How to detect usage of height adjustable table?
                        dougw

                        To measure height use a Maxbotix ultrasonic sensor or a Sharp  GP2Y0A02YK0FGP2Y0A02YK0F or a string pot or a spring and force sensor

                        • Re: How to detect usage of height adjustable table?
                          mcb1

                          So we are trying to register everytime the users changes working position from sitting to standing and from standing to sitting

                          You could use an ultrasonic sensor and detect the height to the ceiling.

                           

                          That would give you a relatively clear path and is uniform.

                          Some code to establish when it's stationery and then record it, or transmit it to a collection device.

                           

                           

                          Cheers

                          Mark

                          2 of 2 people found this helpful
                            • Re: How to detect usage of height adjustable table?
                              balearicdynamics

                              Mark, I think this solution is totally reliable with a very low impact. It has been successfully used by the first drones to detect their height and avoid terrain obstacles. There instead a sensor needed together. Suppose you stay sit on the the desk and it is not rare that your feet impact the sensor. Ok, it can be placed in a very good position but the risk always exists; When I sit to a desk I can have to put downside my backpack, my skateboard, my shoes to wear a more comfortable pair while I am working and so on (these are all real situations I saw while working in the Netherlands past year). So to avoid the ultrasonic (the best solution anyway) is wrong a second sensor should be added to confirm that it is the table moving and not the ground or some part of it.

                              Also for this I see more than one easy solution:

                               

                              • If electronic movement it is sufficient to detect when the motor is on (no matter where it moves, the sensor detect the distance from the gorund (or the relative distance if something is on the ground in that moment).
                              • If manual movement a cap sense placed in proximity of the desk unlock lever is another possible solution for bare mechanical movement
                              • An inertial accelerometer is sufficient put beside the table to inow that it is the table moving instead the rest.

                               

                              Not only but the ultrasonic sensor is able with fewl ines of code to self-calibrate to a relative height when something is put under the table.

                               

                              Enrico

                              1 of 1 people found this helpful
                        • Re: How to detect usage of height adjustable table?
                          dougw

                          Your limit switch idea is a good one. Optical limit switches can easily be shielded from stray light or you can use regular electro-mechanical limit switches.

                          Like a garage door opener function.

                          • Re: How to detect usage of height adjustable table?
                            beacon_dave

                            Are there any restrictions on fitting sensors to the table ? Are you trying to have a device that just sits on the table and logs the information, or can the sensors be physically attached to the table ? Are the tables of the same design ?

                             

                            If you can attach the sensors to the table then:

                            - mechanical limit switches would be a simple choice

                            - a linear encoder could give you more detail about the heights the table was adjusted to

                            - a rotary encoder with rack and pinion arrangement could also be used

                             

                            If the floor covering is giving problems with the likes of ultrasonic sensors then perhaps locate the sensor on the floor so that the reflection is coming off the underside of the solid table rather than off a carpet.

                            1 of 1 people found this helpful
                            • Re: How to detect usage of height adjustable table?
                              koudelad

                              Hello,

                              is the table height adjusted by some electronic control or a manual handle?

                               

                              I use two types of these tables (both electronically controlled) and the manufacturer offers them with two types of controllers. The first one has only up and down keys, the second one has up and down keys, 7 segment display to display the height in centimetres and four keys to store / restore value from a memory. These controllers are interchangeable which means there is probably a rotary encoder on the motor shaft and only one of these controllers can make use of the output The controller of course has then no idea about the ground clearance etc., it just knows the relative position to the lowest position. (Note: I haven't personally dismantled the mechanism.) I would try to do my own version of the controller in this case.

                               

                              If you wanted to attach the measurement sensor to all kinds of mechanical tables (parallel with the floor), an ultrasonic sensor is one of the options. You don't even need to measure the absolute ground clearance, just the difference between the positions.

                              1 of 1 people found this helpful
                              • Re: How to detect usage of height adjustable table?
                                rsc

                                Show us a picture of the table, and we can tell you good places to put sensors.

                                Scott