def add_worksheet(name = '')
      name  = check_sheetname(name)
      worksheet = Worksheet.new(self, @worksheets.size, name)
      @worksheets << worksheet
      worksheet
    end
def add_worksheet(name = '')
      name  = check_sheetname(name)
      worksheet = Worksheet.new(self, @worksheets.size, name)
      @worksheets << worksheet
      worksheet
    end
At least one worksheet should be added to a new workbook. A worksheet is used to write data into cells:

     worksheet1 = workbook.add_worksheet               # Sheet1
     worksheet2 = workbook.add_worksheet('Foglio2')    # Foglio2
     worksheet3 = workbook.add_worksheet('Data')       # Data
     worksheet4 = workbook.add_worksheet               # Sheet4
 If name is not specified the default Excel convention will be followed, i.e. Sheet1, Sheet2, etc.

 The worksheet name must be a valid Excel worksheet name,
 i.e. it cannot contain any of the following characters,
     [ ] : * ? / \

 and it must be less than 32 characters.
 In addition, you cannot use the same, case insensitive,
 sheetname for more than one worksheet.