Operator UI Conventions & Andon Patterns

Purpose

These guidelines describe operator HMI and Andon design patterns that make it fast and safe for frontline workers to understand a situation, take the right action, escalate when necessary, and hand off work to the next shift. The emphasis is on clarity, predictable interactions, and failure-mode safe defaults that reduce stress and mistakes under pressure.

Design principles (high level)

• Action-first: Show the single best next action prominently. Operators should rarely need to hunt for what to do.
• Minimal, prioritized text: Use short action labels, not paragraphs. Reserve explanations for a help pane.
• Consistent visual language: Use the same colors, icons, and layout across screens and devices.
• Predictable escalation: Escalation paths must be obvious, one-tap, and auditable.
• Failure-mode safe defaults: Defaults should err toward safe machine states and clear operator actions.
• Accessible & legible: High contrast, large touch targets, and non-color cues for status.

Information hierarchy & layout

1. Primary (immediate): Current machine/line status and required action (big, centered, top-left). Example: "Stop line — jam detected — Acknowledge / Restart requires supervisor".
2. Secondary (support): Contextual diagnostics: last error code, simple suggested recovery steps, time since fault, responsible role to call.
3. Tertiary (reference): KPIs, recent events log, and links to SOP or maintenance tasks—collapsed by default, expandable if needed.

Color semantics and status

Keep color language small and consistent across the plant. Reserve color for state, not decoration.

• Green: Normal / running
• Amber/Yellow: Warning / degraded performance (requires attention soon)
• Red: Fault / stop — immediate action required
• Blue: Informational (e.g., maintenance scheduled)
• Use shape, icon, and text in addition to color (avoid color-only indicators).

Buttons, acknowledgements, and confirmations

• Primary actions (acknowledge, stop, call) are large, clearly labeled, and positioned consistently.
• Limit confirmation dialogs. Require confirmation only for irreversible or safety-critical actions; otherwise prefer an undoable flow or a brief confirmation tone and visible audit entry.
• Escalation buttons should open a focused modal with a single required field (reason/purpose) and one large "Escalate" button; include recommended contacts by role (not name) to avoid rooster-specific confusion on nights/weekends.

Andon flow pattern (recommended)

1. Operator triggers Andon (big button or pull cord). Screen immediately shows: state, short reason list, and optional free-text.
2. Owner role assigned automatically by rule (line leader / technician). Notifications sent to assigned role (visual + audible + mobile push if available).
3. Assigned responder acknowledges, logs action taken, and either resolves or escalates with a required note.
4. All events are timestamped and recorded to the audit trail for cross-shift handoff and continuous improvement review.

Mobile & maintenance access

Design a compact mobile variant for maintenance supervisors with the same information hierarchy. Keep the primary action and escalation pathways identical to avoid confusion. For mobile:

• Use large tap targets, a single-column layout, and collapsible detail groups.
• Provide offline-capable acknowledgement with queued sync for intermittent connectivity.

Cross-shift handoff and auditability

• Record every acknowledgment, escalation, and resolution with timestamp, role, and optional short note.
• Include an explicit "Handoff summary" button for end-of-shift that produces a short, editable summary of unresolved issues for the next shift.
• Allow supervisors to tag events as "requires root cause review" so CI teams can find them easily.

Accessibility & readability

• Text size: minimum readable font for 24" panels should be 18–22px for body and 28–40px for primary actions (adjust for viewing distance).
• Contrast ratio: meet WCAG AA at minimum for critical text; use bold captions for short distances.
• Icons + text: always pair icons with short labels; avoid ambiguous iconography.

What to display (good defaults)

• Immediate machine status and primary KPI (OEE or takt-related) relevant to current operator tasks.
• Current active alarm with clear next step button (Acknowledge, Call Technician, Ignore with reason).
• Time since event and number of reoccurrences in the shift.
• Quick access to the relevant Standard Work or remediation checklist.

Common anti-patterns to avoid

• Cluttered dashboards showing many KPIs without action pathways.
• False alarms caused by noisy thresholds—display confidence or severity, and allow tuning.
• Multiple equally prominent buttons that make the next step ambiguous.
• Using color alone to indicate critical state.

Testing & success metrics

Validate designs in the shop floor environment and measure:

• Time-to-acknowledge (goal: minimize)
• Time-to-resolution (goal: measurable reduction after UI change)
• False alarm rate (goal: reduce noise)
• Operator error rate during critical flows
• Qualitative operator confidence and satisfaction

Quick implementation checklist

1. Standardize colors, icons, and button layout across all operator screens.
2. Design primary and secondary areas with clear contrast and large touch targets.
3. Implement an Andon flow that forces a short reason and logs timestamped events.
4. Provide supervisor/maintenance mobile view with identical escalation actions.
5. Run a shop-floor usability test with real operators and measure time-to-ack/time-to-resolve.

Micro-templates (copyable text)

• Primary alarm message: "[State] — [Short cause] — [Primary action button]"
• Escalation modal header: "Escalate: [Machine/Line] — Required: brief reason"
• Handoff summary header: "Unresolved items — Action needed by next shift"

Next steps & adaptations

Start with one machine or line: implement the primary action-first layout and the simple Andon flow, measure the success metrics above, then iterate. Consider packaging these patterns into a reusable Plant UI Toolkit so sites can copy and tailor them to local needs.