Robotic arms

[Gary Rubin]

Can anyone recommend a 6-axis robotic arm with about a 1m reach and a payload of about 15kg? The lighter the better.

Thanks,

Gary

[Yair]

Try talking to Schwarzenegger.

Sorry.

[Cat]

Sorry, this topic is not controversial enough for the LAVA Lounge. Where's that "Report to Moderator" button...?

[Gary Rubin]

Sorry, this topic is not controversial enough for the LAVA Lounge. Where's that "Report to Moderator" button...?

But Yair brought up a politician! Doesn't that count??

Sorry.

No need to apologize. I did the same thing in this post.

[Daryl]

Can anyone recommend a 6-axis robotic arm with about a 1m reach and a payload of about 15kg? The lighter the better.

Thanks,

Gary

are you building a sammich maker?

[Gary Rubin]

are you building a sammich maker?

Yes, 15kg ones.

[Daryl]

[PaulG.]

Can anyone recommend a 6-axis robotic arm with about a 1m reach and a payload of about 15kg? The lighter the better.

Thanks,

Gary

Let me Google that for you.

[Gary Rubin]

Let me Google that for you.

Yeah, I found them and a few others as well. I was wondering if anyone had any personal experience with any.

[Wire Warrior]

Remember, chicks dig giant robots.

Jason

[BobHamburger]

Can anyone recommend a 6-axis robotic arm...

Just don't forget that you'll need Old Glory Robot Insurance

[Black Pearl]

There is two kinds of kinematic: Parallel and serial. Parallel kinematics distrubute the forces much better over the robot structure, so they will allow to make them lighter. But their reach is small (google for hexapod). They are also very difficult to design, so there is a few companies that might offer these. Serial kinematics is the classic arm. There also exist some hybrid solutions (3 axis parallel + a serial axis).

If you are looking for the classic arm robot, the big ones in europe are ABB (white), Fanuc (yellow) and Kuka (orange).

For sophisticated solutions I am impressed by Adept. I've once seen a 4-axis parallel-kinematics for pick and place tasks in action and I was really impressed.

Felix

[Yair]

Yes, 15kg ones.

Hmm, manwich.

[PaulG.]

Just don't forget that you'll need Old Glory Robot Insurance

[Daklu]

Yeah, I found them and a few others as well. I was wondering if anyone had any personal experience with any.

I've done some work with a Fanuc robot, though not nearly enough to consider myself an "expert" or even "fairly knowledgable." More along the lines of "knows a few pitfalls and can usually avoid crashing into things." I don't know the model or payload of our robot but it has a range of ~6' end to end.

One thing to be aware of is "singularities." These are joint position combinations within the working area from which the robot controller cannot move because the math returns motion values of +/- infinity or there is an infinite number of solutions. (Such as if two axes are aligned concentrically and parallel.)

On the Fanuc robot there are two types of motion available: Joint motion and Coordinate motion. With joint motion you program the value you want each joint to take. When executed, the controller sets the speed of the joint movement such that all joints reach their desired position and stop at the same time. The path and orientation of the end effecter are not directly controlled by you during the motion; they are a result of the combined motion of all the joints. With coordinate motion you define the motion in coordinate space. The controller directs the joints to move so the end effecter travels in a straight line at a constant speed from point A to point B.

Singularities do not exist in joint motion. They do exist in coordinate motion and make it difficult to access certain regions of the working area. For example, our robot is installed on a wall. Trying to move through the region roughly defined by having the upper arm parallel to the floor and the lower arm pointing straight at the floor was problematic. We hit singularities often because the wrist twist would have to turn infinitely fast (or faster than the robot is capable of) to maintain orientation and speed of the end effecter. Our solution was to move the device being tested so it was positioned under the upper arm instead of right below the elbow. Other solutions could have included programming a coordination motion path around the singularity or switching to joint motion to get through the singularity.

So although a robot may be able to reach all of the locations in its range, it cannot always reach them all using the kind of control you want or need.

Edited December 5, 2009 by Daklu

[Gary Rubin]

Dak,

Thanks for the lengthy response.

I talked to a Fanuc vendor and it seems that all of their arms (at least the ones that vendor carried) were too heavy and power-hungry for our application. I'll have to start thinking about how I can rearrange components to get by with a lighter-duty arm with a shorter reach. The information you provided will allow me to ask some semi-intelligent questions when trying to understand controllers.

Thanks,

Gary

[Cat]

Just don't forget that you'll need Old Glory Robot Insurance

(I can't believe that site hasn't been blocked by Big Brother. Yet.)

[EricLarsen]

Check with Kawasaki Robots. They make numerous robots that might fit your configuration and are a rock solid robotics company.

A 15 kg payload robot is going to be a pretty big one. As payloads and reach go up, the size of the robot goes up almost exponentially. You could easily be looking at a 200kg robot.

[Gary Rubin]

Check with Kawasaki Robots. They make numerous robots that might fit your configuration and are a rock solid robotics company.

A 15 kg payload robot is going to be a pretty big one. As payloads and reach go up, the size of the robot goes up almost exponentially. You could easily be looking at a 200kg robot.

Funny, "exponentially" was the exact term I used when grumbling about the size.

We're looking into rearranging components to get by with a smaller reach and smaller payload.

I'll look into Kawasaki.

Thanks,

Gary

[Daklu]

I agree 15 kg is a pretty heavy payload. Our robot is fairly beefy and IIRC has a 5 kg payload. One question to ask the vendors is if they can support a heavier payload if you use slower speeds with less acceleration.

I'm a little fuzzy on this... perhaps someone else can chime in. I believe the motor driver circuits are current limited. If the current exceeds a certain amount the robot halts with a fault. In the motor, the amount of current is proportional to the torque the motor provides. Since,

Torque = mass * angular acceleration

it holds that reducing the speed and acceleration of the robot will increase your payload. These robots can move very fast. If speed is not a primary concern for your application you may have a lot of room to trade that speed for payload.

Also worth noting is that arm-type robot vendors do not typically quote accuracy specifications since the error varies depending on the position of all the joints. They do quote repeatability though, and these robots are very good at going to a position you've already defined the joint positions for. What's this mean in real terms? If you define a known position in the robot software and then tell it to move 40 cm in *this* direction, how close you get to 40 cm is undefined. (Though still very good. I'd swag worst case accuracy is < 1mm, though I have not specifically investigated it.) However, if you manually jog the robot into the desired position 40 cm away, visually confirm it is in the correct location, and save *that* position data in your software as the second point, it will hit it dead on every time.

[Gary Rubin]

I agree 15 kg is a pretty heavy payload. Our robot is fairly beefy and IIRC has a 5 kg payload. One question to ask the vendors is if they can support a heavier payload if you use slower speeds with less acceleration.

Interesting point.

Also worth noting is that arm-type robot vendors do not typically quote accuracy specifications since the error varies depending on the position of all the joints. They do quote repeatability though, and these robots are very good at going to a position you've already defined the joint positions for. What's this mean in real terms? If you define a known position in the robot software and then tell it to move 40 cm in *this* direction, how close you get to 40 cm is undefined. (Though still very good. I'd swag worst case accuracy is < 1mm, though I have not specifically investigated it.) However, if you manually jog the robot into the desired position 40 cm away, visually confirm it is in the correct location, and save *that* position data in your software as the second point, it will hit it dead on every time.

Our requirement is 2cm, so I'm not too worried about that. We'll also have an external measurement capability that will tell us where it is, so we can then adjust if necessary.

[EricLarsen]

I agree 15 kg is a pretty heavy payload. Our robot is fairly beefy and IIRC has a 5 kg payload. One question to ask the vendors is if they can support a heavier payload if you use slower speeds with less acceleration.

I'm a little fuzzy on this... perhaps someone else can chime in. I believe the motor driver circuits are current limited. If the current exceeds a certain amount the robot halts with a fault. In the motor, the amount of current is proportional to the torque the motor provides. Since,

Torque = mass * angular acceleration

it holds that reducing the speed and acceleration of the robot will increase your payload. These robots can move very fast. If speed is not a primary concern for your application you may have a lot of room to trade that speed for payload.

You are partially correct on this. Decreasing speed and acceleration can increase a robot's payload a bit. However, motor torque is only part of the equation. There are also bearing loads, belt tensions, mounting bolt strengths, motor brake strengths, and so on. All these can have an impact on payloads. Robots are actually designed for bigger loads than they are rated for. For example, our custom robot we use was rated for 30kg, but the was actually tested at around 40kg. By the way, our 30kg 'bot weighs in at about 450kg. So the curve isn't quite exponential, but you get the idea.

However, the manufacturer is very unlikely to give you the green light to run with a higher than rated payload, and I think you would be taking a gamble. What if a programming error on your part caused the robot to run with too high of an acceleration? Could be pretty hard on some very expensive equipment and would most likely void a warranty.