All DHD4D units are designed for maximum uptime with minimum maintenance. The unit does not require any kind of lubrication or special maintenance procedure throughout its lifetime. However there are exceptional occasions where you may need to perform some maintenance:

Finger segments: maintaining a smooth motion

The finger segments are actuated by a combination of Kevlar reinforced tendons and springs. They are designed to require no lubrication. However it is convenient to clean any debris or dirt from the segments regularly, especially if their movement is not smooth or if you find any joint to have a “jerky” reaction. You can clean the joints using a small tool that fits the gaps, such as a small x-knife. Bend the joint manually and slide the x-knife through the joint, making sure to avoid the tendon!

What happens if I distend a tendon

It is uncommon to distend a tendon: all tendons are put through a process of holding a heavy object to ensure their inner threading is tight after being manufactured. However with time, wear and heavy loads it is possible they distend slightly or settle in the pulley. This won't affect the functionality of your hand. However a sign of distended tendons is that, when closing your hand, it only starts moving once you have a position in the tens of units. While it this does not affect the functionality or durability of the unit it reduces the resolution of motion.

To fix this, you simply need to readjust the tendon on the pulley. Please follow the steps below to perform this task.

Replacing a Tendon

A broken tendon is a very unlikely event - as they are made from Kevlar reinforce materials - but may happen as a result of excess force or wear. Your hand should have come with spare tendons. (if by any reason you need extra tendons because they were lost, damaged or any other reason, please get in touch as we'll be able to provide spares).

Replacing the tendon is a multi step process:

  1. Remove the top cover from the hand. Please pay special attention when lifting the cover as the cables for the actuators are connected to this top part.
  2. Undo the screws that secure the broken tendon to the pulley
  3. Remove the broken tendon from the hand
  4. On the finger itself, remove the other part of the tendon. To do this, remove any material that covers the fingertip to expose the screw that holds the tendon.
  5. Undo the screw on the finger tip and remove the tendon

Now it's time to install the new tendon. Taken a spare one from the set you received.

  1. First, slide the new tendon from the finger tip, through all the segments up to the base. (this is a bit like threading a needle so be patient and persistent)
  2. Next slide the tendon all the way through until the knot at the end is aligned with the screw hole on the finger tip.
  3. Reinstall the screw on the fingertip to secure the tendon, being careful not to over-tighten it. These screws are very fragile; as long as they are slightly below the surface of the fingertip, they should be fine.
  4. Test the tendon mobility by holding the base of the finger and pulling on the tendon: the finger should close when the tendon is pulled and open, once it is released.
  5. Now insert the tendon in the palm, sliding it through the round opening between the two magnets. Again, this is a little like threading a needle, so be patient. The tendon should come out through the bowden tube inside the hand.
  6. Now it's time to attach it to the pulley. This is done by following the procedure below for readjusting the tendons on the pulleys.

Replacing a finger

Fingers are designed with a magnetic attachment system to allow them to cope with excess lateral forces without being damaged. They can self align most of the times by simply closing the hand. However, in the unlikely event that you break a finger on your Robot hand, they can be easily replaced.

Replacing a finger is actually easier than replacing a tendon, as you won't have to deal with removing the damaged tendon and inserting a new one.

The steps to replace a finger are a subset of the steps required to replace a tendon:

  • Remove the top cover from the hand. Please pay special attention when lifting the cover as the cables for the actuators are connected to this top part.
  • Follow steps 5 and 6 of the instructions to replace a tendon: insert the tendon in the palm, sliding it through the round opening between the two magnets and proceed to the instructions on how to attach it to the pulley.

Readjusting or attaching a tendon on the pulley

The procedure of readjusting or re installing a tendon on the pulley is one accuracy. The pulleys were specially designed to make the fine adjustment of tendons as easy as possible but it may take a couple of attempts to get it right the first time you do it.

There are several ways to do this, but here we describe the one we use when we assemble the hands:

  1. Remove the top cover from the hand if you haven't done so yet. Please pay special attention when lifting the cover as the cables for the actuators are connected to this top part.
  2. Identify where your tendon connects (which pulley and which screw)
  3. Unscrew the center screw that attaches the pulley to the servo shaft. Do not remove the pulley from the shaft; only the screw. The tendons are installed around this screw just for safety though.
  4. Now loosen the hex screw that secures your tendon and free it from the screw.
  5. VERY IMPORTANT: this is a key step: you should now apply power and connect the hand to the computer. Using either the Console, Bluetooth or the protocol, we set torque on for that joint and set position to 0. This will ensure the pulley is at the correct position for the finger to be fully distended. Be careful when doing this as the interior of the hand will be exposed. Make sure your hands are safely away from the inside of the hand when it's moving.
  6. Maintain power and torque applied on the joint.
  7. Now pull the tendon until you feel it is just tight and roll it 3-5 times around the hex screw.
  8. Now holding the finger straight, bolt the Hex screw to secure the tendon.
  9. At this point you can use the Console, Bluetooth or the protocol to move the finger a few times and ensure it has the correct range of motion and is not exhibiting a “distended” behavior (meaning the finger will immediately start moving when you set position to the first few units). If the range is not as desired, go back to step 4.
  10. Now re-insert the center screw on the pulley and roll the tendon(s) 3-4 times around the screw.
  11. Now fasten the screw to complete the re-assembly procedure.
  12. Finally close the hand by re installing the top cover. Make sure to distribute the cabling inside so that it does not affect the motion of the tendons.

That's it! Your hand is now back in top shape!

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  • dh4d/maintenance.txt
  • Last modified: 2016/03/21 12:54
  • by wadmin