da Vinci 5 Force Feedback instruments: Spot the difference

Quick post here to show you the massive difference between standard Xi Instruments and the new Force Feedback Instruments: Look at the images below and see if you can spot the differences before I point them out.

Xi Cadiere grasper

DV5 Force Feedback Cadiere grasper

So examine the difference between the Top picture (the Xi Cadiere) and the bottom picture (DV5 Force Feedback Cadiere)

Shaft and end effector interface on Force Feedback Instruments

Number 1: The black shaft to instrument tip interface is radically different. In the old XI it was an almost linear transition zone. What we can see here is a reduce diameter and then a flared end assembly that holds the instrument wrist and tip. This is a big design change.

I cannot imagine that this is just cosmetic. I wonder if it is partly to do with assembly - and improving ease of assembly and economics (part of the change). So maybe making a more "universal shaft"? Where you can just "slot on" any of the force feedback end assemblies.

It may also (in Part) be cosmetic to show a very differentiated instrument - to make them very distinguishable and "feel higher end"? Because they do look higher end and more functional.

But my highest suspicion is that it somehow helps with the force feedback - there may be some reason you don't want the black shaft directly attached to the "business end" - but that is speculation. It could be that forces or vibrations in the black shaft as it passes the trocar valve could be transmitted to the tip - and that "break" in continuity may help to remove some of the "noise" in the signal.

It has to be meaningful - as it is an expensive design change.

I am also just suspecting that any Force Feedback (FF) instrument would need to be even more rigid. This could also be a material change in the shaft - or a thickness change of the material?

If you are using the drive cables inside to measure forces and you get "flex" in the shaft. One cable on one side would end up with less tension (small amounts) and on the opposite side, higher amounts of tension. Those tension differentials due to "flex" would show up in un reliable force measurements. So maybe this design has even more rigidity in the shaft? (It's a Guess without trying to bend both).

Quality of the pins

Number 2: The quality of the securing pins that hold all of the wrist joints together has improved massively. (And they look expensive.) More below on fabrication technique differences.

The fact there is a sort of black grub screw at the back of the wrist assembly (where it attaches onto the shaft) makes me wonder again if this is an improved "universal" assembly that they are going for. That would be a way to try and reduce manufacturing costs and have less parts in the parts bin. (Later at least). If so let this be a lesson to all about having good DFM (Design for manufacture early in your R&D process.)

DV5 force feedback Maryland

Close up Force Feedback Maryland

XI Maryland

Take a close look at the above three images. And look for these differences in the Maryland Bipolar between Xi and DV5.

Shift to monofilament cabling

Number 3: Probably the most significant change in the instruments. The keen eyed will see (and know) that the cables that move the wrists in Xi Instruments are braided Tungsten cables. They are very expensive - but last well and do the job well.

It is clear in the images of the DV5 Force feedback instruments they have changed these cables. They are now a black - non braided - polymer cables.

What does this mean. Much of the force feedback sensing is measured by the load and forces at the tip of the instrument - that gets transmitted back up the shaft by those drive cables - to the drive interfaces. Those drive interfaces have torque sensors that measure the forces being applied.

Tungsten braised cables may give two problems:

First is that a braided surface running over pulleys will create a lot of noise in the signal. A monofilament smooth cable will reduce that rub noise in the signal.

Next, tungsten cables do have a degree of stretch in them (all braided cables do) and some sensitivity to reprocessing and a host of other minor issues that for driving instruments is not important - but for transmitting clear and accurate signals back - they could (could) not be suitable. They may not be able to stay within tolerances enough be used in a reliable way for the force feedback.

So "Why not make a smooth tungsten cable?" - breakage - and some other technical reasons about bending around corners, memory and a host of stuff.

The answer is to move to some form of polymer monofilament cable.

Finally cost. Tungsten cables are hellish expensive. I imagine (but could be wrong) that if you can move to polymer monofilament cables - they could have some cost savings long term? It could also have some advantages in how you fix them to the other components in the assembly process - making it easier and more cost effective.

Change to machined components

Number 4: In early production models it is not common to immediately go to high yield - high manufacture components. It is normal for instruments like the Xi (once you know everything about the parts right) to got to MIM parts (Metal injection moulded) parts.

I suspect what you see on the Xi instruments are all MIM parts - lower cost - higher volume - but not quite as nice (Subjective for the manufacturing engineers). But ideal for high volume manufacturing (once you have all the kinks ironed out of the system.)

It looks to me that those gorgeous Force Feedback instruments are sporting highly machined parts. Lower volume but often higher tolerances. They are way more expensive - but in lower volumes it makes sense - and you can make changes faster should you get feedback from the market as you build data.

To me that would signal they want accuracy and reliability in the early launch (as opposed to margin) and use of the instruments need to be well accepted. Jamie (CFO Intuitive) was very clear that the FF instruments would have much "worse" gross margins. This is clearly one of the reasons - as these components would be multiples of times more expensive. But the device has a higher chance of giving early customer satisfaction.

Others

From the images I've seen, this is about all I can figure out so far. What I know from being in this field so long is that precision is essential in motion of the instruments and functionality. But that goes up radically when you then want to measure accurately the forces at the tip.

So I am sure there are a lot of "under the hood" changes of components - routing - connectors - plastics moulding etc that is not visible here. But all of that (at lower volumes would indicate the higher cost to make and lower margins.). Intuitive indicated a 9% net bump in price per case for use of FF instruments. That's a complex calculation due to product mix. But read it as "They will cost more." So be the premium instruments.

It is going to be interesting to see how well they are accepted by the community. I suspect - very well by novices, newbies, and Lowe skilled surgeons. Less so by hard core robotic surgeons. Until they see the data that even in their hands - less force gets applied to tissue when they turn on the FF.

All of this is just speculation and opinion of the author based on images and publicly disclosed information.