By Tomer Lanzman
Lowly priced digital calipers have been available on the market for some years. Most of them are produced in China or the Far East and possess a serial interface, over which measuring data can be transferred to other devices. Despite their price ($10 - $20) these calipers are very reliable and precise. Apart from the original use as calipers, they can be used as position display or Digital Readout DRO for linear axles of small machine tools in the same way as linear glass scales. For this purpose digital scale readouts with mounting brackets are available in different lengths. In small CNC machines these scales can serve as reference givers and tool length givers. Even a 3D Digitizer / 3D Scanner for 3D measurements as well as tensile tests can be easily implemented. A complete workshop can be digitized for little money.
fig. 1: Sample Application of the Caliper2PC Interface, Screenshots Excel Interface and Caliper2PC Software.
To use the measuring data (capturing, displaying, converting etc.), it is necessary to connect the digital calipers to a PC using their serial interfaces. For this purpose the interface and multiplexer Caliper2PC has been developed and is described here (see video).
Within the scope of this project the hardware and software required to equip the machines accordingly have been designed. The result is a future-oriented, user-friendly and adaptable system which offers aside from the numerous implemented features, space for own additions (API - software interface).
fig. 2: Milling Machine with Caliper2PC DRO X,Y,Z and glass scales.
fig. 3: Optimum Lathe with Caliper2PC DRO and Touchscreen.
The communication between the multiplexer Caliper2PC and the host PC occurs via USB. No external power supply is required, since the Caliper2PC is power-supplied by USB from the host PC. The Caliper2PC offers on the input side connections for up to 6 digital calipers. This way it is possible to connect, for example, a milling machine (3 axes; x-, y-, and z-axis), a lathe (2 axes) and an additional digital caliper for the QA (see fig. 1). To connect the digital calipers to the Caliper2PC interface, a connecting lead must be attached (see chapters "Pin Assignment" and "Retrofitting Calipers" ).
All supported linear encoders can be used simultaniously (e.g. glass scales, linear scales and Mitutoyo Digimatic devices). The DROs can be reset to zero or to any given value in any position. For every linear encoder the Caliper2PC interface offers an additional input port for an edge finder or to connect a pedal switch to capture the momentary value for instance (see chapter "Retrofit with Capture Button"). Alternatively, reference switches or end switches used with CNC machines can be connected to detect and process the switch states. The Caliper2PC software can be used with a webcam as a video edge finder.
In addition, two tachometers are implemented in the Caliper2PC interface. This allows displaying and regulating tool machines' spindle speeds.
Copyright © Tomer Lanzman.
All rights reserved.
Copyright © Tomer Lanzman. All rights reserved.