Rails Gem "Axlsx" - Rename Workbook

My workbook always named like my template "invoices_generate.xlsx". How can i rename this File ?

Template "invoices_generate.xlsx.axlsx" :

wb = xlsx_package.workbook

    wb.add_worksheet(:name => "Beleg") do |sheet|  

    .
    .
    .

    sheet.column_widths 2 , 11, 11, 11, 11, 23, 3

    end