Using a circulating fluid becomes less desirable if you need a quick change, because one of the main advantages of the approach is the large reservoir of liquid at the desired temperature. It may still be a viable approach, just a little less attractive now.

Since the hand is metal, it conducts heat well and it's going to feel cold at ambient temperature. I don't think you'd ever need to actively cool it unless ambient temp is over 90°F or so. So maybe you can simplify your project a LOT by using a resistive heater such as nichrome wire and concede defeat on the cooling.

Do you have a plan to measure the temperature of the user's hand and the robot's hand? Your ability to have a good feedback loop will depend on the speed and precision of determining the ∆T. You can employ a control scheme as simple as a bang-bang (on or off) thermostat, or you might want to learn about a PLC approach to provide a more elegant heating control.

 

I am not aware of any organization outside of the medical systems companies dealing with temperature controlled systems on a small scale. When I designed the one system, the internet was not yet very mature. No websites selling stuff yet.Small low-flow pumps are available as are all of the connecting hardware.
For me to research current suppliers, professional fees will apply. (not cheap)
Medical grade plastic tube will be appropriate, two aquarium heaters will be able to provide fluid at two chosen temperatures, and simple solenoid valves will be able to select which temperature fluid becomes circulated.
But using a hard metal hand does not seem suitable for the project as described.

 

 

Of course a heat pump will be more efficient, but efficiency is not the issue here, but rather applicability and effectiveness are the primary concerns. To that end, consider where the cold side heatsink would be located.
If we had a drawing of the hand or a photo that could allow some consideration and possibly a good suggestion.
I am guessing that the hand is a cast aluminum part with no flat surfaces at all.
I suggest reading whatever application material is available about the use of Peltier devices.

 

Hello.
I have done a similar post but didn`t find a solution] so I am doing again with more information and specification.
I am working on a projection human interaction with robot. When a person hold the hand of robot he will tell a story. The story lasts for less than a minute. I want to match the temperature of robot hand to that of the person who hold it. I will measure the temperature of the person hand first and then I will try to make the temperature of robot hand accordindly. The robot hand is made of hard metal as shown in the attachment.
I need valuable suggestions how to control the temperature of robot hand and it is possible to install or attach something on robot hand that can work.

 

I think one immediate problem is that not every user will grip that hand the same way. I would instinctively avoid putting any part of my body within the gripping fingers but I can imagine other people attempting a handshake-type grip.

Are you planning to measure temperature in just one spot? You'll need to make sure the user does in fact contact that spot. You might consider an IR gun-type measurement, meaning non-contact and fast.

Is there room inside that hand for electronics and a heating element of some kind? IR panels (used in dry saunas) might be an option to radiate heat at the users hand instead of relying only on conduction.

Just throwing out ideas.

Edit: Here's another one. Just put an insulating coating on the hand. The coating will "reflect" the temperature of the user. No electronics needed.

 

The objective is to change the temperature of robot hand and then to analyze the effect of change in temperature between robot hand and human hand. The difference can be upto 4 degrees. So in all cases I have to control that is increase or decrease the temperature of robot hand. what can be the possible solution?

 

Ah, I'm beginning to get it. You want to look at the effect of robot hand temperature, versus user hand, on the perception of the message?

This is a very difficult challenge since both surfaces, the robot hand and the user's skin, are in contact and affecting each other. Ideally you could monitor and control the FLOW of heat. The temperature perceived by the user depends on whether heat is moving in or out, and the magnitude of that flow. Entering a pool at say, 85°F after sunbathing is hard because the water feels cold compared to your hot skin. That same 85°F pool feels great in the winter when you jump in with cold skin.

Would it be possible to have a separate touch panel or such to measure the user's hand BEFORE they grasp the robot hand? That would allow a pre-heating.

 

The change in temperature between person and robot hand is exactly what we want. The change can be upto 4 degress. ofcourse the temperature of the person hand is to be measured first separately and then the temperature of robot hand is set accordingly. I need something to change and control the temperature of the robot hand.

 

The change in temperature between person and robot hand is exactly what we want. The change can be upto 4 degress. ofcourse the temperature of the person hand is to be measured first separately and then the temperature of robot hand is set accordingly. I need something to change and control the temperature of the robot hand.

I think you have a reasonable chance of doing this using only a heating element and of course the controller. Some individuals will have hands cold enough that the robot hand at ambient may not feel cold and perhaps you'll just have to accept a less than 100% success rate. But most people grabbing metal at ambient (below 80°F) will perceive it as "cool" to the touch. Your heater can go up from there. I'd consider using a light bulb as the heater.

I think a TEC cooling system in that space would be very difficult since it would require a heat sink and probably a fan as well. You MIGHT get away with only the heat sink if you run the TEC well below its rated max current. There are heat sinks specifically designed for no-fan applications.

 

Hello,
Thank you for the suggestion.
If I am going to use a light then why not I go straight with the heater? Also give me your precious suggestions on heat pump of thransfering heat through fluid.

 

Well, the thermal mass (it’s a loose term, I should have said heat capacity) is specified in J/K° (Joules per Kelvin). It tells you what it takes to influence a thing concerning its temperature. You need to have some idea just how much energy you are going to need to get the robot hand to the set point temperature from the ambient one.

You will also need to know how long it will be before the ambient temperature influences the manipulator temperature to the point of needing to use active temperature management again.

This is because you have to figure out if the Peltier is going to suffer self heating to the point that it can’t be used to manage the temperature any more. Think of this: the Peltier hot side is extracting heat from the cold side and everything it is thermally coupled to. If you turn off the device, the hot side will begin to heat the cold side and its thermal neighbor.

If the hot side gets too hot, it won’t be able to provide the differential needed to cool the robot, and it will end up doing nothing or even heating it. To prevent this, the hot side needs some sort of cooling. This can be done with an appropriate heatsink, but that has to be exposed to the air so it can lose heat by radiation and convection. Since radiation is a fairly weak way to cool things, and convection in an ordinary room is limited, a fan is usually used on the heatsink.

Can you accommodate an exposed heatsink and possibly a fan on the robot where the Peltier will be mounted?

One possibility would be to remotely mount the Peltier, that is remote from the hand, not from the robot, and use a heat pipe to thermally attach it. I would recommend getting a small Peltier and doing some tests. In the absence of someone having the thermal management design skills to simulate or calculate this, empirical results will give you an idea if the Peltier stands a chance.

It might work just fine, but despite being really cool things (no pun intended) the reality of them is so often very disappointing. They don’t “just work“ as we’d like them to.

Hello,
Can you explain the idea of mounting the peltier remotely to hand of robot. I mean how to use a heat pipe on peltier, your guidence will be appreciated.

 

Hello,
Can you explain the idea of mounting the peltier remotely to hand of robot. I mean how to use a heat pipe on peltier, your guidence will be appreciated.

Something like this, attached to the Peltier mounted on the robot arm, and to something like an aluminum plate on the hand, would allow a low profile attachment to the hand, Experimentation would be required to work out the control scheme with, presumably a PID controller.

 

Something like this, attached to the Peltier mounted on the robot arm, and to something like an aluminum plate on the hand, would allow a low profile attachment to the hand, Experimentation would be required to work out the control scheme with, presumably a PID controller.

OK, that depends also on the distance. Also the amount of time it will take to obtain the desire tempeture. Would you share something regarding liquid temperature control system?

 

OK, that depends also on the distance. Also the amount of time it will take to obtain the desire tempeture. Would you share something regarding liquid temperature control system?

Using a pumped fluid would allow for verity fast transfer of heat. It wouldn’t be much different, except it would have a pump. By coupling the hand to a mass of liquid, you would easily keep it at the temperature of the liquid.

The optimization problem becomes deciding on the thermal mass of the liquid to balance thermal stability with responsiveness. It the robot hand just has to stay at fixed temperature, with slow changes being adequate, a large amount of liquid would be good. If it need to be more responsive, a reduced amount would be called for.

Water can be used, and it has the advantages of being readily available and relatively harmless (in the case of a leak, etc.), but it’s best to used distilled water to eliminate mineral content that could precipitate onto the walls, as well as an antimicrobial/antifungal agent to prevent the growth of mold and the like inside the closed system.

Oil, such as mineral oil, can also be used though a leak could be a big mess. The advantage of oil is its inferior heat capacity. This might sound odd but it means that you can more readily heat and cool it. It will take less time to react to a change in temperature, which might (or might not) be important.

The bottom line is that by circulating a liquid through the hand you will be able to maintain the temperature as if the hand had more thermal mass since it becomes a tightly coupled part of the system of the liquid and the temperature control (heating and cooling). If you place the pump and heater-cooler element(s) at a distance, and/or in a sound proof box, you could also use something like an aggressive fan to participate in the cooling, and possibly resistive heating to increase the efficiency of the hot side of the heat-cool mechanism using the peltier only for cooling.

 

Of course the "ultimate" solution would be to have both a hot sink and a cold sink available, hot and cold running water, and then control the mixed flow going to the hand to meet whatever temperature you need in between the hold and cold sink temperatures.