VSM Studio
VSM guide / Lean tools / Poka-yoke (error proofing)
Poka-yoke (error proofing)
Log the defects at a step, see them on a Pareto chart, dig into the top one with 5 whys, and plan poka-yoke devices by type (contact, fixed-value, motion-step) and function (prevent or detect). In the builder, the AI suggests devices for each defect. Free, no sign-up.
Poka-yoke in three steps
1. Find the biggest defects
Count each defect for a week and where it's found. The Pareto chart shows the few that make up most of the problem; those found by the customer (red) come first.
2. Ask why five times
Get from the symptom ("part loaded backwards") to the cause you can design out ("the fixture accepts both orientations").
3. Design the device
Contact devices sense shape, size or position. Fixed-value devices count parts or actions. Motion-step devices enforce the sequence.
Prevent beats detect
A prevent device makes the mistake impossible or stops the process. A detect device warns that it happened. Inspection and checklists are the last resort.
Poka-yoke examples
An offset pin so a part only fits one way; a counter that won't release the fixture until 4 screws are torqued; a parts tray with one pocket per component so a leftover screw is obvious; a light curtain that stops the press if the hand is in the die; a connector shaped so it can't be plugged into the wrong socket.
In the VSM Studio builder, open Error proofing on a process box: Apply lowers the step's scrap and rework by the planned reduction, so first-pass yield and load on the map update.
Questions
What does poka-yoke mean?
Japanese for "mistake-proofing", from Shigeo Shingo. Devices or methods that make it impossible, or immediately obvious, to do a step wrong.
What are the three types of poka-yoke?
Contact (senses physical features like shape or position), fixed-value (checks that a fixed number of parts or movements happened) and motion-step (checks that steps happen in the right order).
What is the difference between prevention and detection?
Prevention (control) stops the error before a defect is made, for example a fixture that only accepts the right orientation. Detection (warning) signals a defect right after it happens so it does not move on.
How do I pick which defect to error-proof first?
The tallest bars on the Pareto, weighted up for anything that reaches the customer. A cheap prevent device on the top defect usually pays back fastest.