Turn a PLC into a REST API.

What your code sees

GET /plc/line-3/tags
→ every tag with its type, range and whether it can be written

POST /plc/line-3/conveyor
{ "speed_mm_s": 120, "dir": "fwd" }

GET /plc/line-3/conveyor
→ { "speed_mm_s": 120, "dir": "fwd", "running": true }

WS /plc/line-3/stream
→ tag changes as they happen

POST /plc/line-3/heartbeat

POST /plc/line-3/conveyor
{ "speed_mm_s": 400 }
→ 422 { "reason": "out_of_range", "range": [0, 300] }

The tag map

Our engineers go through your I/O list and PLC program with you and write this file. Each tag has a name, an address, a type, a range and whether it can be written. A new version goes on the box only after both our engineer and your engineer approve it.

plc: line-3
protocol: modbus-tcp
host: 192.168.10.20        # control network port
cycle_ms: 50
heartbeat: { expect_every_ms: 100, timeout_ms: 300 }
watchdog:  { addr: HR 40100, every_ms: 100 }   # the PLC rung watches this
tags:
  conveyor.speed_mm_s:
    addr: HR 40001
    type: uint16
    range: [0, 300]
    max_step: 50                     # largest change in one write
    write: true
    requires: [cell.door_closed]     # writable only while this is true
  conveyor.dir:      { addr: HR 40002, type: enum, values: { fwd: 1, rev: 2 }, write: true }
  conveyor.running:  { addr: DI 10001, type: bool, write: false }
  cell.door_closed:  { addr: DI 10005, type: bool, write: false }
safe_state:
  conveyor.speed_mm_s: 0

Addresses that belong to emergency stops, safety PLCs, safety scanners or muting cannot be put in a tag map. The validator refuses them.

Every write goes through the same checks

In this order. The first check that fails refuses the write, and nothing is sent to the PLC.

1. 01Write keyThe key switch on the box is set to write. Turn it to read-only and every write is refused, whatever the software says.
2. 02Not stoppedThe box has not fallen to its safe state since the last operator reset.
3. 03Known tagThe tag is in the tag map and marked writable.
4. 04Typeuint16 gets an integer, enum gets one of its names, bool gets true or false.
5. 05RangeInside the tag's range. Outside is refused, not clipped.
6. 06StepThe change from the current value is within max_step, so nothing jumps.
7. 07ConditionsEvery tag in requires is true, read from the PLC on the latest cycle. A stale reading counts as false.
8. 08One writerEach tag has one writer at a time. A second client cannot fight the first.

How it stops

A box that can only stop the machine itself is not enough: if the box freezes, nothing stops. So the PLC watches the box. Edge Box increments a watchdog register every 100 ms; one rung in the PLC stops the outputs that Edge Box can command if that value stops changing.

Restart is always by a person: the key set to write, then an operator reset. Edge Box never resumes on its own. It sits on top of emergency stops, safety PLCs and other certified safety functions; it does not replace them.

What's in the box

Pilot units are built from off-the-shelf industrial parts. We will pick the exact model with our first design partners.

Security

• The control network port and your network port are never bridged, routed or NATed inside the box.
• The API listens only on your network port, over TLS, with a token per client. Each token can be limited to certain tags.
• Nothing on the internet can open a connection to the box. Remote support uses a tunnel the box opens outward, only when you allow it.
• Every write and every refusal is logged with the time, the client, the tag and the value. Kept on the box for 30 days and exportable.

PLCs and protocols

We start with Modbus TCP, which most PLCs can be set to speak. Native protocols come next, in the order our design partners need them.

Edge Box talks to the PLC, not to field devices. It does not join fieldbuses such as PROFINET or EtherCAT directly.

Getting the first box running

1. 01Read the I/O togetherRemotely, with your I/O list and PLC program. We write the tag map.
2. 02RehearseRun your code against a PLC simulator, or against real equipment in PAI-Ground, using the same tag map.
3. 03InstallDIN rail, 24 V, two network cables. We add the watchdog rung to the PLC with your engineer.
4. 04Start read-onlyRun read-only for a few days and check the values match. Then enable writes one tag at a time.

What Edge Box does not do

• Replace emergency stops, safety PLCs or safety laser scanners.
• Write or generate ladder logic, apart from the watchdog rung.
• Plan motion. Trajectories and cycle times stay in your code or the existing PLC program.
• Depend on the cloud. Writing and stopping work with only the box and the PLC.