Define a task

Example

Imagine a robot arm fixed to a table. Its tip is the point we want to move. All three exercises use this same arm. The numbers and results are fictional teaching examples, not evidence from a robot run.

We measure from a mark at the arm’s base. Forward is X, left is Y and up is Z. This fixed measuring system is called a coordinate frame. The base mark is its origin, where X, Y and Z are zero.

Our target is 20 cm forward, directly in line with the base and 15 cm above it. We will call the task successful if the tip ends within 1 cm of that target. This allowed distance is the tolerance.

Your turn

Write your answer on paper or think it through before checking:

1. Complete the target in centimetres: X = __, Y = __, Z = __.

2. The saved task uses metres. Choose the correct saved target: A: (20, 0, 15) m or B: (0.20, 0, 0.15) m. Remember: 100 cm = 1 m.

3. The tip stops 2 cm from the target. Does it meet our success rule?

4. You rotate your view of the table. Do the target’s coordinates change if our measuring system stays fixed?

Check your reasoning

1. X = 20 cm, Y = 0 cm, Z = 15 cm. Y is zero because the target is neither left nor right of the base.

2. B: (0.20, 0, 0.15) m. Divide centimetres by 100. Option A would ask for a point 20 metres forward and 15 metres up.

3. No. An error of 2 cm is larger than the allowed 1 cm. We need a measured final position to check this rule. A target marker alone cannot show success.

4. No. Rotating the view changes how we see the table, not our fixed measuring system or target.

You have specified where the tip should go and how you will judge the result. In the next exercise, distinguish that request from a prediction and a measurement.