Have each button call a different controller and send them the input data

<form action="#" id="form">
                  <div class="col-sm-12">
                    <div class='col-md-4'>
                      <div class="form-group ">
                          <label for="validationDefault01">Fecha Inicio</label>
                            <div class="input-group">
                              <input class="form-control" id="date_inicio" name="date_inicio" placeholder="YYYY/MM/DD" type="text"/>
                              <div class="input-group-addon">
                                <i class="fa fa-calendar"></i>
                              </div>
                           </div>
                      </div>
                    </div>

                    <div class='col-md-4'>
                        <div class="form-group">
                          <label for="validationDefault01">Fecha Fin</label>
                            <div class='input-group date' id='datetimepicker7'>
                              <input class="form-control" id="date_fin" name="date_fin" placeholder="YYYY/MM/DD" type="text"/>
                              <div class="input-group-addon">
                                <i class="fa fa-calendar"></i>
                              </div>
                            </div>
                        </div>
                    </div>

                    <div class='col-md-4'>
                      <br>
                      <button type="button" class="btn btn-primary" onclick="filtrar()"><i class="fa fa-filter"></i> Filtrar</button>
              
                      <button type="button" class="btn btn-danger" href="<?=base_url()?>index.php/login_controller/generar_pdf"><i class="fa fa-file-pdf-o"></i> Export PDF</button>
                      
                      <button type="button" class="btn btn-success" href="<?=base_url()?>index.php/login_controller/generar_excel"><i class="fa fa-file-excel-o"></i> Export EXCEL</button>
                    </div>

                  </div>
                </form>