In order to use multiple signature pad in a single page, you have to assign the id for the canvas element dynamically. For example change the below line in initControl function from
Code:
this.canvasID = Ext.id(null, 'thecanvas');
this.cmp.html = '<canvas width="' + width + '" height="' + height + '" style="border:1px solid black;" id=' + this.canvasID + '></canvas>';
to
Code:
this.canvasID = Ext.id(null, 'thecanvas');
this.cmp.html = '<canvas width="' + width + '" height="' + height + '" style="border:1px solid black;" id=' + this.canvasID + '></canvas>';